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Diagnostic Value of Isolated Mentalis Versus Mentalis Plus Upper Limb Electromyography in Idiopathic REM Sleep Behavior Disorder Patients Eventually Developing a Neurodegenerative Syndrome

Diagnostic Value of Isolated Mentalis Versus Mentalis Plus Upper Limb Electromyography in... Abstract Study Objectives: To compare two electromyographic (EMG) montages, isolated mentalis muscle versus mentalis in combination with upper limb muscles in the baseline diagnostic video-polysomnography (V-PSG) of patients with idiopathic REM sleep behaviors disorder (IRBD) who eventually were diagnosed with a clinically defined neurodegenerative syndrome. Methods: Forty-nine patients were included. At baseline, diagnosis of RBD was based on a typical history of dream enactment behaviors plus V-PSG showing REM sleep with qualitative increased EMG activity and/or abnormal behaviors. Quantification of EMG activity (tonic, phasic and “any”) in the mentalis and upper limb muscles (biceps brachii-BB, n = 36 or flexor digitorum superficialis-FDS, n = 13) was performed manually and compared with published cut-offs. Results: Nine (18.4%) patients had either tonic or phasic EMG below the cut-offs for the isolated mentalis and four of them (11.1 %) also had values below the cut-off for the mentalis combined with BB. All 13 patients recorded with the FDS were above the mentalis combined with FDS cut-off. For the diagnosis of IRBD, sensitivity of isolated mentalis was 81.6% and of the combination of mentalis plus upper limb muscles was 91.8% (p = .03). Audiovisual analysis showed abnormal REM sleep behaviors in all nine patients with values below the cut-offs. Conclusion: Quantification of EMG activity in the upper limbs combined with the mentalis increases the ability to diagnose IRBD when compared with the isolated measurement of the mentalis. Detection of typical abnormal behaviors during REM sleep with audiovisual analysis is essential for the diagnosis of IRBD in patients with EMG values below the published cut-offs. Idiopathic REM sleep behavior disorder, electromyographic quantification, mentalis, upper limbs, flexor digitorum superficialis, biceps brachii. Statement of Significance A correct diagnosis of idiopathic REM sleep behavior disorder (IRBD) is crucial because it carries a high risk of a neurodegenerative disease. Our study compares two currently used electromyographic montages, isolated mentalis versus mentalis combined with upper limb muscles in the baseline video-polysomnogram of IRBD patients who later developed a neurodegenerative syndrome. We found that the montage of mentalis combined with upper limbs identifies best patients with IRBD. However, video-recording of abnormal behaviors in REM sleep is essential to diagnose the condition in a small subset of patients with EMG values within the normal range. These findings are relevant to increase the diagnostic accuracy of IRBD while using video-polysomnography. INTRODUCTION REM sleep behavior disorder (RBD) is a parasomnia characterized by nightmares and repeated episodes of abnormal movements and vocalizations during REM sleep.1–3 An accurate diagnosis of RBD is particularly important in idiopathic RBD (IRBD) because the parasomnia usually heralds a defined neurodegenerative syndrome such as mild cognitive impairment (MCI), dementia with Lewy bodies (DLB), Parkinson disease (PD) or more rarely multiple system atrophy (MSA).4–7 Video-polysomnography (V-PSG) showing excessive amounts of sustained (tonic) or intermittent (phasic) electromyographic (EMG) activity during REM sleep is required for the diagnosis of RBD.2 The definition of what constitutes “excessive” EMG activity and the body muscles where it should be measured have been the focus of several studies.8–11 For the diagnosis of IRBD, quantification of EMG activity exclusively in the mentalis muscle is a common practice in many sleep centers since this muscle is routinely used for sleep scoring.12 Isolated quantification of EMG activity of the mentalis has good discriminative power8–10 and cut-off levels of 30% for tonic and 15% for phasic EMG activity have been proposed for the correct identification of IRBD.9 EMG recording of the mentalis, however, is prone to include breathing and snoring artifacts and may be atonic in epochs in which abnormal behaviors typical of RBD occur only in the limbs.10,11 Therefore, investigators have examined additional muscles for the diagnosis of IRBD.11 The anterior tibialis has low discriminative power because this muscle in healthy people often shows benign distal movements which are not specific for RBD.9,10 In contrast, EMG activity in upper limb muscles, such as the flexor digitorum superficialis (FDS) or the biceps brachii (BB), in addition to the mentalis, has a high discriminative power11 when using cut-off levels of 31.9% and 21.8%, respectively.10 It is currently unclear which method of quantification is preferable to diagnose IRBD. Ideally, the optimal system would be the one that best identifies patients with IRBD. However, since there is not an independent marker or a gold standard for diagnosis of IRBD other than V-PSG, there is some circularity in this issue: only subjects with high amounts of EMG activity in REM sleep are diagnosed with IRBD, whereas those with lower amounts (but displaying some typical RBD manifestations in REM sleep) may not be diagnosed with the condition. For instance, one study using EMG quantification9 only in the mentalis found values within normal range in 11.8% of subjects diagnosed with IRBD using clinical history. Other studies have also found some overlap in the values of EMG activity between patients and controls.10,13 These observations indicate that there are patients with a clinical picture highly suggestive of IRBD that have EMG values within the proposed normal range of EMG activity during REM sleep. One way to overcome these difficulties is to study patients that were diagnosed initially with IRBD and eventually developed a defined neurodegenerative syndrome. Since IRBD in those patients was “per se” an early manifestation of the underlying disease, it is reasonable to assume that their clinical picture corresponded to “true” IRBD, no matter the quantity of EMG activity found in the baseline V-PSG study. The aim of this study was to compare quantitative EMG measures between the isolated mentalis and the combination of the mentalis with upper limb muscles in the baseline diagnostic V-PSG of IRBD patients who later developed a defined neurodegenerative syndrome. This would elucidate which EMG montage in PSG is more adequate for the diagnosis of IRBD. METHODS Patient Selection We selected all patients who were diagnosed with IRBD at the Hospital Clinic de Barcelona, Barcelona, Spain, from January 2000 to June 2015. Diagnosis of IRBD in our center required: (1) clinical history of dream-enacting behaviors; (2) V-PSG showing REM sleep with qualitative increased EMG activity and/or abnormal movements/behaviors in REM sleep; and (3) and absence of a defined neurodegenerative syndrome. We did not establish a minimal amount of EMG activity in REM sleep if clear dream-enactment behaviors typical of RBD (eg, prominent body jerking, punching, kicking, shouting) were detected during REM sleep in the videotape analysis. When the diagnosis of IRBD was made, patients were clinically followed-up as previously described.5 We identified 49 patients who developed a clinically defined neurodegenerative syndrome disease (PD, DLB, MCI or MSA) according to current criteria.14–17 In order for the scorer of EMG activity not to be influenced by the knowledge that the patients were diagnosed with a defined neurodegenerative syndrome, V-PSG studies from IRBD patients with similar age and gender distribution who remained disease-free after at least 5 years of follow-up (n = 36) were also quantified. All the studies were anonymized and the scorer was blind for the outcome (converted to a defined neurodegenerative syndrome or remained disease-free). The results of EMG quantification of the patients who remained disease-free were not used in this study. Exclusion criteria were treatment with antidepressants, melatonin and benzodiazepines (including clonazepam) at the time of the baseline V-PSG, and technical artifacts preventing proper EMG quantification. We did not exclude patients that showed mild to moderate obstructive sleep apnea in V-PSG but we carefully excluded from quantification all REM sleep epochs with respiratory-related EMG increases (regular breathing, snoring or apnea/hypopnea-induced arousals). The ethics committee of Hospital Clinic of Barcelona approved this study. Polysomnographic Variables All patients underwent a full-night PSG study with synchronized audiovisual recording with a digital polygraph (Deltamed, software version 1998, Paris, France). V-PSG included electroencephalogram (EEG) (C3, C4, O1, and O2, referred to the contralateral ear; F3 and F4 were added in 2007), right and left electro-oculograms, surface mentalis EMG and right and left anterior tibialis EMG. From 2000 to 2007 we recorded upper limb EMG activity from right and left BB, and in the right and left FDS from 2007 to 2015.11 V-PSG also included electrocardiogram, nasal and oral air-flow assessment, thoracic and abdominal movement assessment, body position and measurement of oxyhemoglobin saturation. Sleep stages were scored according to American Academy of Sleep Medicine12 criteria with allowance to score REM sleep despite excessive EMG activity in the mentalis muscle channel. The occurrence of the first rapid eye movement was used to determine the onset of a REM sleep stage. The end of a REM sleep stage was determined when either no REMs were detected in three consecutive minutes or an awakening, K complex, or spindles were observed.12 A new REM sleep stage was considered when it occurred 30 minutes after the previous episode. Analysis of EMG Activity In each V-PSG study, quantification of tonic, phasic, and “any” (either tonic or phasic) EMG activity was performed manually during REM sleep. EMG activity in REM sleep was quantified using 30-second epochs and 3-second miniepochs. All movement artifacts and increases in EMG tone due to arousals were excluded from analysis. A trained sleep scorer (AF) who was blinded to the patient’s outcome (converted to a defined neurodegenerative syndrome or remained disease-free) performed the EMG quantification. In doubtful cases, the recordings were reviewed and discussed with the rest of the team until agreement was reached. The EMG activity was analyzed in all channels using a sampling rate of 256 Hz, a low-frequency filter at 10 Hz, high-frequency filter at 100 Hz, and a display sensitivity of 5 μV/mm. Impedances of surface EMG electrodes had to be lower than 10 kΩ. Tonic EMG activity was scored only in the mentalis muscle channel using 30-second epochs with a display sensitivity of 5 μV/mm although in case of doubt a 3 μV/mm display and/or a ruler were used to better discriminate the signal amplitude. The reference background EMG signal was the lowest one recorded in the same REM sleep stage analyzed, or if continuous EMG activity in REM sleep occurred, the one recorded in the most stable and relaxed adjacent previous NREM sleep epochs. Each epoch was scored as “tonic” in the mentalis when the increased sustained EMG activity was present in more than 50% of the total 30-second epoch duration with an amplitude of at least twice the background EMG activity or more than 10 µV. The periods of PSG shorter than a full 30-second epoch of sleep, mainly occurring at the end of each REM sleep stage, were not included in the analysis. The rate of tonic EMG activity was calculated as the number of 30-second epochs with this EMG activity divided by the whole number of 30-second epochs during REM sleep. Phasic EMG activity of three muscles (mentalis and either right and left BB or right and left FDS) was quantified during REM sleep. Each EMG channel was displayed isolated on the computer screen and scored independently from the other muscles. After the scoring of a muscle was completed, the process was repeated in the remaining two muscles. Phasic EMG events were defined as any burst of EMG activity lasting 0.1–5 seconds with an amplitude exceeding twice the background EMG activity during REM sleep. Each 3-second miniepoch in each EMG channel was scored as “0” when phasic EMG activity was absent and “1” when phasic EMG activity was present. Three-second miniepochs were also scored as having or not having “any” EMG activity, irrespective of whether it contained tonic, phasic or a combination of both types of EMG activity in the mentalis. The rates of phasic and “any” EMG activity in the mentalis were calculated as the proportion of 3-second miniepochs during REM sleep containing the corresponding type of muscle activity. In the upper limbs only phasic EMG activity was quantified and the proportion of 3-second miniepochs during REM sleep containing this type of EMG activity was calculated. In addition, we scored the rates of “any” EMG activity in the mentalis associated with phasic EMG activity in the right and left upper limbs. In this EMG montage a 3-second miniepoch was computed as having EMG activity when at least one of the three muscles evaluated had EMG activity (at least one score of “1”), and as not having EMG activity when none of the muscles in the combination had “any” or phasic EMG activity measure. Classification of Patients According to Different Cut-Offs and Emerging Disease We identified the number of patients with EMG activity rates below previously published cut-offs for IRBD diagnosis. For the isolated mentalis muscle we used the cut-off of ≥30% for tonic EMG activity or ≥15% for phasic EMG activity, as reference, as previously published.9 For the combination of mentalis plus upper limb muscles we used the cut-off of ≥31.9% for “any” EMG activity in the mentalis with the right and left FDS (SINBAR montage) and of ≥21.8 % for “any” mentalis with the right and left BB.10 Video Analysis When EMG measurements during REM sleep did not reach the previously published proposed cut-offs, we reviewed the video tapes of the same V-PSG studies to see if they contained the typical abnormal movements, behaviors and vocalizations displayed by patients with IRBD during REM sleep. Visual analysis was performed in conjunction with the PSG recording and the excluded epochs (due to respiratory events, eg,) during the quantification were also excluded from the video analysis. The intensity of these manifestations was classified as mild, moderate or severe according to a system previously described in our center.18 Statistical Analysis Descriptive demographic, clinical and PSG data are given as mean ± standard deviations, counts and frequencies. Comparison of demographic variables between the group of patients who developed a defined a neurodegenerative syndrome and those who remained idiopathic was done with a chi square test and T-Student, as appropriated. Comparison of rates of EMG activity between the different defined neurodegenerative syndromes was performed with T-Student. Since sensitivity of mentalis combined with upper limb muscles should ever be equal or greater than the mentalis alone, comparison of sensitivities was done with unilateral binomial tests. SPSS 19 for Windows (SPSS, Inc., Chicago, IL) was used for all statistical analyses. RESULTS Demographic, Clinical, and PSG Data We studied 49 patients (43 men) with IRBD who later were diagnosed with a clinically defined neurodegenerative syndrome (15 PD, 19 DLB, 2 MSA and 13 MCI) at the age of 73.6 ± 5.1 (range, 60–85) years and after a mean follow-up of 4.7 ± 3.1 years. Mean age at diagnosis of IRBD was 68.6 ± 5.3 years. There were no significant differences in demographic variables between patients who developed a clinically defined neurodegenerative syndrome and those who remained disease-free (Table 1). Table 1 Demographic Characteristics of IRBD Patients Who Developed a Clinically Defined Neurodegenerative Syndrome and Those Who Remained Idiopathic. Demographic variables N Not remained idiopathic Remained idiopathic p 49 36 Sex, male (n, %) 43 (87.8%) 26 (72.2%) .070 Age at estimated IRBD onset (years) 62.1 ± 5.6 61.5 ± 8.3 .702 (range, 50–73) (range, 44–77) Interval from estimated IRBD onset to diagnosis of IRBD by V-PSG (years) 6.5 ± 5.5 5.1 ± 4.2 .192 (range, 1–25) (range, 1–20) Age at IRBD diagnosis (years) 68.6 ± 5.3 66.7 ± 7.4 .157 (range, 56–78) (range, 49–79) Follow-up (years)a 4.7 ± 3.1 7.9 ± 2.12 .001 (range, 0.5–12) (range, 5–13) Demographic variables N Not remained idiopathic Remained idiopathic p 49 36 Sex, male (n, %) 43 (87.8%) 26 (72.2%) .070 Age at estimated IRBD onset (years) 62.1 ± 5.6 61.5 ± 8.3 .702 (range, 50–73) (range, 44–77) Interval from estimated IRBD onset to diagnosis of IRBD by V-PSG (years) 6.5 ± 5.5 5.1 ± 4.2 .192 (range, 1–25) (range, 1–20) Age at IRBD diagnosis (years) 68.6 ± 5.3 66.7 ± 7.4 .157 (range, 56–78) (range, 49–79) Follow-up (years)a 4.7 ± 3.1 7.9 ± 2.12 .001 (range, 0.5–12) (range, 5–13) IRBD = idiopathic REM sleep behavior disorder; V-PSG = video-polysomnography. Values are expressed as mean ± standard deviation and range, frequency and percentage. V-PSG: polysomnography with audiovisual recording. aInterval from diagnosis of IRBD in our sleep center to diagnosis of a clinically defined neurodegenerative syndrome or to the last visit in those subjects who remained idiopathic. Open in new tab Table 1 Demographic Characteristics of IRBD Patients Who Developed a Clinically Defined Neurodegenerative Syndrome and Those Who Remained Idiopathic. Demographic variables N Not remained idiopathic Remained idiopathic p 49 36 Sex, male (n, %) 43 (87.8%) 26 (72.2%) .070 Age at estimated IRBD onset (years) 62.1 ± 5.6 61.5 ± 8.3 .702 (range, 50–73) (range, 44–77) Interval from estimated IRBD onset to diagnosis of IRBD by V-PSG (years) 6.5 ± 5.5 5.1 ± 4.2 .192 (range, 1–25) (range, 1–20) Age at IRBD diagnosis (years) 68.6 ± 5.3 66.7 ± 7.4 .157 (range, 56–78) (range, 49–79) Follow-up (years)a 4.7 ± 3.1 7.9 ± 2.12 .001 (range, 0.5–12) (range, 5–13) Demographic variables N Not remained idiopathic Remained idiopathic p 49 36 Sex, male (n, %) 43 (87.8%) 26 (72.2%) .070 Age at estimated IRBD onset (years) 62.1 ± 5.6 61.5 ± 8.3 .702 (range, 50–73) (range, 44–77) Interval from estimated IRBD onset to diagnosis of IRBD by V-PSG (years) 6.5 ± 5.5 5.1 ± 4.2 .192 (range, 1–25) (range, 1–20) Age at IRBD diagnosis (years) 68.6 ± 5.3 66.7 ± 7.4 .157 (range, 56–78) (range, 49–79) Follow-up (years)a 4.7 ± 3.1 7.9 ± 2.12 .001 (range, 0.5–12) (range, 5–13) IRBD = idiopathic REM sleep behavior disorder; V-PSG = video-polysomnography. Values are expressed as mean ± standard deviation and range, frequency and percentage. V-PSG: polysomnography with audiovisual recording. aInterval from diagnosis of IRBD in our sleep center to diagnosis of a clinically defined neurodegenerative syndrome or to the last visit in those subjects who remained idiopathic. Open in new tab Polysomnographic data are shown in Table 2. A mean of 89.1 ± 42.9 epochs and 964.0 ± 444.6 3-second miniepochs of REM sleep were analyzed. The mean apnea/hypoapnea index (AHI) was 14.7 ± 16.2. Twenty-eight (57.1%) patients had AHI lower than 10. Six of these 28 were previously diagnosed with obstructive sleep apnea syndrome, were effectively treated with continuous positive airway pressure and wore the mask during their diagnostic V-PSG. Sixteen patients (32.6%) had an AHI greater than 15. Five of these 16 patients had apneas and hypopneas exclusively related to the supine position but REM sleep was recorded in the lateral position not containing respiratory-related arousals. Eleven (22.4%) patients had an AHI greater than 15 with a mean AHI during REM sleep of 32.5 ± 14.7 (range, 17.8–62.7). In these 11 patients, we carefully excluded from EMG analysis the 30-second epochs and 3-second miniepochs containing respiratory related arousals or awakenings. The excluded epochs were 37.0 ± 18.9 % of the total epochs in REM sleep leaving 82.6 ± 24.5 epochs for analysis. The number of scored 30-second epochs and 3-second miniepochs was similar in the group of 11 patients with apneic events during REM sleep and the 38 remaining patients (82.6 ± 24.5 vs. 91.0 ± 47.0, p = .576 and 910.4 ± 247.2 vs. 979.5 ± 488.7, p = .655, respectively). Table 2 Polysomnographic Variables of the 49 Patients With IRBD Who Eventually Developed a Clinically Defined Neurodegenerative Syndrome. Time in bed, min 464.5 ± 42.8 Total sleep time, min 345.3 ± 62.9 Sleep efficiency, % 74.4 ± 12.0 Wake after sleep onset, min 95.2 ± 58.0 Sleep stage, %  N1 22.3 ± 11.4  N2 44.0 ± 9.4  N3 15.1 ± 10.1  REM 15.6 ± 7.3 Sleep-onset latency, min 21.5 ± 14.1 REM sleep latency, min 114.7 ± 80.4 REM sleep stages, n 2.8 ± 1.0 30-s epochs, n 89.1 ± 42.9 3-s miniepochs, n 964.0 ± 444.6 AHI index 14.7 ± 16.2 PLMS index 18.7 ± 25.9 Time in bed, min 464.5 ± 42.8 Total sleep time, min 345.3 ± 62.9 Sleep efficiency, % 74.4 ± 12.0 Wake after sleep onset, min 95.2 ± 58.0 Sleep stage, %  N1 22.3 ± 11.4  N2 44.0 ± 9.4  N3 15.1 ± 10.1  REM 15.6 ± 7.3 Sleep-onset latency, min 21.5 ± 14.1 REM sleep latency, min 114.7 ± 80.4 REM sleep stages, n 2.8 ± 1.0 30-s epochs, n 89.1 ± 42.9 3-s miniepochs, n 964.0 ± 444.6 AHI index 14.7 ± 16.2 PLMS index 18.7 ± 25.9 AHI = apnea-hypoapnea index (number of apneas and hypoapneas per hour of sleep); IRBD = idiopathic REM sleep behavior disorder; PLMS index = periodic leg movements in sleep (number of periodic leg movements in sleep per hour of sleep); REM = rapid eye movement. Values are expressed as mean ± standard deviation. Open in new tab Table 2 Polysomnographic Variables of the 49 Patients With IRBD Who Eventually Developed a Clinically Defined Neurodegenerative Syndrome. Time in bed, min 464.5 ± 42.8 Total sleep time, min 345.3 ± 62.9 Sleep efficiency, % 74.4 ± 12.0 Wake after sleep onset, min 95.2 ± 58.0 Sleep stage, %  N1 22.3 ± 11.4  N2 44.0 ± 9.4  N3 15.1 ± 10.1  REM 15.6 ± 7.3 Sleep-onset latency, min 21.5 ± 14.1 REM sleep latency, min 114.7 ± 80.4 REM sleep stages, n 2.8 ± 1.0 30-s epochs, n 89.1 ± 42.9 3-s miniepochs, n 964.0 ± 444.6 AHI index 14.7 ± 16.2 PLMS index 18.7 ± 25.9 Time in bed, min 464.5 ± 42.8 Total sleep time, min 345.3 ± 62.9 Sleep efficiency, % 74.4 ± 12.0 Wake after sleep onset, min 95.2 ± 58.0 Sleep stage, %  N1 22.3 ± 11.4  N2 44.0 ± 9.4  N3 15.1 ± 10.1  REM 15.6 ± 7.3 Sleep-onset latency, min 21.5 ± 14.1 REM sleep latency, min 114.7 ± 80.4 REM sleep stages, n 2.8 ± 1.0 30-s epochs, n 89.1 ± 42.9 3-s miniepochs, n 964.0 ± 444.6 AHI index 14.7 ± 16.2 PLMS index 18.7 ± 25.9 AHI = apnea-hypoapnea index (number of apneas and hypoapneas per hour of sleep); IRBD = idiopathic REM sleep behavior disorder; PLMS index = periodic leg movements in sleep (number of periodic leg movements in sleep per hour of sleep); REM = rapid eye movement. Values are expressed as mean ± standard deviation. Open in new tab Quantification of EMG Activity and Audiovisual Analysis Rates of tonic, phasic and “any” EMG activity in individual and combined muscles are shown in Table 3. Table 3 Electromyographic Activity of the 49 Patients Who Eventually Developed a Clinically Defined Neurodegenerative Syndrome. Muscle Tonic EMG activity in the mentalis (%) 33.8 ± 33.8 (0–95.9) Phasic EMG activity in the mentalis (%) 29.2 ± 15.3 (8.2–74.9) “Any” EMG activity in the mentalis (%) 49.5 ± 28.1 (8.2–93.0) Combined “any” EMG activity in the mentalis with bilateral phasic BB (%) (n = 36) 56.2 ± 27.2 (8.9–94.7) Combined “any” EMG activity in the mentalis with bilateral phasic FDS (%) (n = 13) 67.4 ± 20.1 (37.8–96.3) Phasic EMG activity in the right BB (n = 36) 17.2 ± 13.3 (1.3–52.3) Phasic EMG activity in the left BB (n = 36) 17.0 ± 15.0 (0.5–56.3) Phasic EMG activity in right FDS (%) (n = 13) 19.6 ± 13.7 (2.4–51.7) Phasic EMG activity in left FDS (%) (n = 13) 20.3 ± 11.3 (4.4–41.3) Muscle Tonic EMG activity in the mentalis (%) 33.8 ± 33.8 (0–95.9) Phasic EMG activity in the mentalis (%) 29.2 ± 15.3 (8.2–74.9) “Any” EMG activity in the mentalis (%) 49.5 ± 28.1 (8.2–93.0) Combined “any” EMG activity in the mentalis with bilateral phasic BB (%) (n = 36) 56.2 ± 27.2 (8.9–94.7) Combined “any” EMG activity in the mentalis with bilateral phasic FDS (%) (n = 13) 67.4 ± 20.1 (37.8–96.3) Phasic EMG activity in the right BB (n = 36) 17.2 ± 13.3 (1.3–52.3) Phasic EMG activity in the left BB (n = 36) 17.0 ± 15.0 (0.5–56.3) Phasic EMG activity in right FDS (%) (n = 13) 19.6 ± 13.7 (2.4–51.7) Phasic EMG activity in left FDS (%) (n = 13) 20.3 ± 11.3 (4.4–41.3) BB = biceps brachii; EMG = electromyography; FDS = flexor digitorum superficialis.Values are expressed as mean ± standard deviation and range. Open in new tab Table 3 Electromyographic Activity of the 49 Patients Who Eventually Developed a Clinically Defined Neurodegenerative Syndrome. Muscle Tonic EMG activity in the mentalis (%) 33.8 ± 33.8 (0–95.9) Phasic EMG activity in the mentalis (%) 29.2 ± 15.3 (8.2–74.9) “Any” EMG activity in the mentalis (%) 49.5 ± 28.1 (8.2–93.0) Combined “any” EMG activity in the mentalis with bilateral phasic BB (%) (n = 36) 56.2 ± 27.2 (8.9–94.7) Combined “any” EMG activity in the mentalis with bilateral phasic FDS (%) (n = 13) 67.4 ± 20.1 (37.8–96.3) Phasic EMG activity in the right BB (n = 36) 17.2 ± 13.3 (1.3–52.3) Phasic EMG activity in the left BB (n = 36) 17.0 ± 15.0 (0.5–56.3) Phasic EMG activity in right FDS (%) (n = 13) 19.6 ± 13.7 (2.4–51.7) Phasic EMG activity in left FDS (%) (n = 13) 20.3 ± 11.3 (4.4–41.3) Muscle Tonic EMG activity in the mentalis (%) 33.8 ± 33.8 (0–95.9) Phasic EMG activity in the mentalis (%) 29.2 ± 15.3 (8.2–74.9) “Any” EMG activity in the mentalis (%) 49.5 ± 28.1 (8.2–93.0) Combined “any” EMG activity in the mentalis with bilateral phasic BB (%) (n = 36) 56.2 ± 27.2 (8.9–94.7) Combined “any” EMG activity in the mentalis with bilateral phasic FDS (%) (n = 13) 67.4 ± 20.1 (37.8–96.3) Phasic EMG activity in the right BB (n = 36) 17.2 ± 13.3 (1.3–52.3) Phasic EMG activity in the left BB (n = 36) 17.0 ± 15.0 (0.5–56.3) Phasic EMG activity in right FDS (%) (n = 13) 19.6 ± 13.7 (2.4–51.7) Phasic EMG activity in left FDS (%) (n = 13) 20.3 ± 11.3 (4.4–41.3) BB = biceps brachii; EMG = electromyography; FDS = flexor digitorum superficialis.Values are expressed as mean ± standard deviation and range. Open in new tab Twenty-seven (55.1%) patients did not reach the ≥30% cut-off for tonic EMG activity in the mentalis and nine of them had values below the 15% cut-off for phasic EMG activity. Therefore, nine (18.4%) patients had “normal” values of EMG activity in the mentalis (Figure 1, Table 4). Evaluation of the audiovisual recordings of these nine patients during REM sleep showed abnormal manifestations typical of RBD that were classified as mild in six patients, moderate in one and severe in two (Table 4). V-PSG also excluded RBD potential mimics (eg, severe obstructive sleep apnea, prominent periodic leg movements in sleep, NREM sleep parasomnias, nocturnal epilepsy) in these nine individuals. Figure 1 Open in new tabDownload slide Percentages of tonic EMG activity (1a) and phasic EMG activity (1b) in the mentalis of the 49 patients who eventually developed a clinically defined neurodegenerative syndrome (horizontal bar indicates the previously published proposed cut-off of 30% and 15% respectively).9 Figure 1 Open in new tabDownload slide Percentages of tonic EMG activity (1a) and phasic EMG activity (1b) in the mentalis of the 49 patients who eventually developed a clinically defined neurodegenerative syndrome (horizontal bar indicates the previously published proposed cut-off of 30% and 15% respectively).9 Table 4 Electromyographic Activity Measures and Audiovisual Findings in the Nine Patients Who Had Electromyographic Activity in the Mentalis Below the Proposed Cut-Offs for the Diagnosis of RBD. Patient Emerging condition Tonic EMG activity in the mentalis (%) Phasic EMG activity in the mentalis (%) “Any” EMG activity in the mentalis plus phasic EMG activity in upper limbs (%) Severity and types of abnormal manifestations typical of RBD detected in the audiovisual recordings during REM sleepa 1 DLB 21.6b 8.6b 48.8 (BB) Moderate (upper limbs elevation with jerks) 2 MCI 3.7b 13.6b 44.0 (FDS) Severe (lower limbs kicking) 3 PD 2.3b 12.1b 28.4 (BB) Mild (proximal four limbs jerking) 4 MCI 0b 10.6b 25.9 (BB) Mild (proximal four limbs jerking) 5 DLB 1.0b 14.4b 22.9 (BB) Mild (proximal four limbs jerking) 6 DLB 3.8b 10.9b 17.6b (BB) Mild (lower limbs jerking and repetitive hand movements) 7 MCI 1.4b 10.8b 15.0b (BB) Mild (sudden moderate trunk and four limbs jerking) 8 PD 2.8b 8.7b 13.5b (BB) Mild (proximal lower limbs jerking) 9 MCI 0b 8.2b 8.9b (BB) Severe (repetitive lower limbs kicking) Patient Emerging condition Tonic EMG activity in the mentalis (%) Phasic EMG activity in the mentalis (%) “Any” EMG activity in the mentalis plus phasic EMG activity in upper limbs (%) Severity and types of abnormal manifestations typical of RBD detected in the audiovisual recordings during REM sleepa 1 DLB 21.6b 8.6b 48.8 (BB) Moderate (upper limbs elevation with jerks) 2 MCI 3.7b 13.6b 44.0 (FDS) Severe (lower limbs kicking) 3 PD 2.3b 12.1b 28.4 (BB) Mild (proximal four limbs jerking) 4 MCI 0b 10.6b 25.9 (BB) Mild (proximal four limbs jerking) 5 DLB 1.0b 14.4b 22.9 (BB) Mild (proximal four limbs jerking) 6 DLB 3.8b 10.9b 17.6b (BB) Mild (lower limbs jerking and repetitive hand movements) 7 MCI 1.4b 10.8b 15.0b (BB) Mild (sudden moderate trunk and four limbs jerking) 8 PD 2.8b 8.7b 13.5b (BB) Mild (proximal lower limbs jerking) 9 MCI 0b 8.2b 8.9b (BB) Severe (repetitive lower limbs kicking) BB = biceps brachii; DLB = dementia with Lewy bodies; FDS = flexor digitorum superficialis; MCI = mild cognitive impairment; MSA = multiple system atrophy; PD = Parkinson disease; RBD = REM sleep behavior disorder. Values are expressed as percentages. aNone of the nine patients had vocalizations during the recording. bRates below the proposed cut-offs for the diagnosis of IRBD (the proposed cut-offs for the diagnosis of IRBD are the following: ≥30% for tonic EMG activity in the mentalis, ≥15% for phasic EMG in the mentalis, ≥21.8% for “any” EMG activity in the mentalis plus bilateral biceps brachii, and ≥31.9 for “any” EMG activity in the mentalis plus bilateral flexor digitorum superficialis). Open in new tab Table 4 Electromyographic Activity Measures and Audiovisual Findings in the Nine Patients Who Had Electromyographic Activity in the Mentalis Below the Proposed Cut-Offs for the Diagnosis of RBD. Patient Emerging condition Tonic EMG activity in the mentalis (%) Phasic EMG activity in the mentalis (%) “Any” EMG activity in the mentalis plus phasic EMG activity in upper limbs (%) Severity and types of abnormal manifestations typical of RBD detected in the audiovisual recordings during REM sleepa 1 DLB 21.6b 8.6b 48.8 (BB) Moderate (upper limbs elevation with jerks) 2 MCI 3.7b 13.6b 44.0 (FDS) Severe (lower limbs kicking) 3 PD 2.3b 12.1b 28.4 (BB) Mild (proximal four limbs jerking) 4 MCI 0b 10.6b 25.9 (BB) Mild (proximal four limbs jerking) 5 DLB 1.0b 14.4b 22.9 (BB) Mild (proximal four limbs jerking) 6 DLB 3.8b 10.9b 17.6b (BB) Mild (lower limbs jerking and repetitive hand movements) 7 MCI 1.4b 10.8b 15.0b (BB) Mild (sudden moderate trunk and four limbs jerking) 8 PD 2.8b 8.7b 13.5b (BB) Mild (proximal lower limbs jerking) 9 MCI 0b 8.2b 8.9b (BB) Severe (repetitive lower limbs kicking) Patient Emerging condition Tonic EMG activity in the mentalis (%) Phasic EMG activity in the mentalis (%) “Any” EMG activity in the mentalis plus phasic EMG activity in upper limbs (%) Severity and types of abnormal manifestations typical of RBD detected in the audiovisual recordings during REM sleepa 1 DLB 21.6b 8.6b 48.8 (BB) Moderate (upper limbs elevation with jerks) 2 MCI 3.7b 13.6b 44.0 (FDS) Severe (lower limbs kicking) 3 PD 2.3b 12.1b 28.4 (BB) Mild (proximal four limbs jerking) 4 MCI 0b 10.6b 25.9 (BB) Mild (proximal four limbs jerking) 5 DLB 1.0b 14.4b 22.9 (BB) Mild (proximal four limbs jerking) 6 DLB 3.8b 10.9b 17.6b (BB) Mild (lower limbs jerking and repetitive hand movements) 7 MCI 1.4b 10.8b 15.0b (BB) Mild (sudden moderate trunk and four limbs jerking) 8 PD 2.8b 8.7b 13.5b (BB) Mild (proximal lower limbs jerking) 9 MCI 0b 8.2b 8.9b (BB) Severe (repetitive lower limbs kicking) BB = biceps brachii; DLB = dementia with Lewy bodies; FDS = flexor digitorum superficialis; MCI = mild cognitive impairment; MSA = multiple system atrophy; PD = Parkinson disease; RBD = REM sleep behavior disorder. Values are expressed as percentages. aNone of the nine patients had vocalizations during the recording. bRates below the proposed cut-offs for the diagnosis of IRBD (the proposed cut-offs for the diagnosis of IRBD are the following: ≥30% for tonic EMG activity in the mentalis, ≥15% for phasic EMG in the mentalis, ≥21.8% for “any” EMG activity in the mentalis plus bilateral biceps brachii, and ≥31.9 for “any” EMG activity in the mentalis plus bilateral flexor digitorum superficialis). Open in new tab Follow-up of these nine subjects showed that two eventually developed PD, three DLB and four MCI. The mean age at diagnostic V-PSG in this group of nine patients was 69.7 ± 4.7 years, the mean estimated RBD duration was 7.4 ± 6.9 years and the mean number of scored 3-second miniepochs was 953.1 ± 256.4. All nine individuals were men and four (44.4%) were referred to our sleep center because of other sleep complaints and not because of the dream-enacting behaviors (two because unexplained hypersomnolence and two for suspected obstructive sleep apnea). However, in these four patients specific questioning during the semistructured sleep interview at their first visit demonstrated a concomitant chronic history typical of RBD. In 36 (73.5%) patients the upper limb EMG activity was evaluated in the BB and in the remaining 13 (26.5%) in the FDS. All the 13 patients who underwent V-PSG using the EMG SINBAR montage (mentalis plus bilateral FDS) had EMG values above the cut-off for the diagnosis of IRBD (≥31.9%; Figure 2a). Four (11%) of the 36 patients who underwent baseline V-PSG using the EMG montage of the mentalis plus bilateral BB had EMG values below the cut-off for the diagnosis of IRBD (≥21.8%; Figure 2b). All four subjects did not reach either the tonic (≥30%) or the phasic (≥15%) cut-offs values using only the mentalis. In all of them the audiovisual recordings showed abnormal manifestation typical of RBD (Table 4). Follow-up of these four subjects showed that one eventually developed PD, one DLB and two MCI. Figure 2 Open in new tabDownload slide (2a) Percentages of “any” EMG activity in the mentalis plus phasic EMG activity in the bilateral flexor digitorum superficialis (FDS) of the 13 patients who eventually developed a clinically defined neurodegenerative syndrome using this EMG montage (horizontal bar indicates the previously published proposed cut-off of 31.9%) (2b) Percentages of “any” EMG activity in the mentalis plus phasic EMG activity in the bilateral biceps brachii (BB) of the 36 patients who eventually developed a clinically defined neurodegenerative syndrome using this EMG montage (horizontal bar indicates the previously published proposed cut-off of 21.8%).10 Figure 2 Open in new tabDownload slide (2a) Percentages of “any” EMG activity in the mentalis plus phasic EMG activity in the bilateral flexor digitorum superficialis (FDS) of the 13 patients who eventually developed a clinically defined neurodegenerative syndrome using this EMG montage (horizontal bar indicates the previously published proposed cut-off of 31.9%) (2b) Percentages of “any” EMG activity in the mentalis plus phasic EMG activity in the bilateral biceps brachii (BB) of the 36 patients who eventually developed a clinically defined neurodegenerative syndrome using this EMG montage (horizontal bar indicates the previously published proposed cut-off of 21.8%).10 Overall, for the diagnosis of IRBD, quantification of EMG activity in the mentalis plus upper limb muscles had a sensitivity of 91.8%, whereas the sensitivity for the isolated mentalis was of 81.6% (unilateral binomial test, p = .03). The rates of tonic EMG activity (Table 5) in the mentalis muscle in the 15 patients who developed PD were significantly higher than those of the 32 patients that developed DLB or MCI or in the 19 who developed DLB. There were no significant differences in the measurement of phasic EMG activity in the mentalis and in the measurement of combined “any” EMG activity in the mentalis with bilateral phasic BB between patients who developed PD and those who developed DLB or MCI or in the patients who developed DLB. There were not sufficient patients on the groups of each neurodegenerative syndrome to compare the measurement of combined “any” EMG activity in the mentalis with bilateral phasic FDS. Table 5 EMG Activity in Each Type of Emerging Disease. PD (n = 15) DLB (n = 19) MCI (n = 13) p (PD vs. DLB) p (PD vs. DLB + MCI) Tonic EMG activity in mentalis (%) 48.2 ± 36.5a 24.6 ± 25.4 27.2 ± 38.1 .036 .034 Phasic EMG activity in mentalis (%) 35.4 ± 19.4 26.5 ± 10.9 26.4 ± 16.0 .103 .069 Combined “any” EMG activity in mentalis with bilateral phasic BB (%) (n = 36)a 63.8 ± 31.4 (n = 11) 54.9 ± 20.2 (n = 16) 42.3 ± 34.0 (n = 7) .377 .238 PD (n = 15) DLB (n = 19) MCI (n = 13) p (PD vs. DLB) p (PD vs. DLB + MCI) Tonic EMG activity in mentalis (%) 48.2 ± 36.5a 24.6 ± 25.4 27.2 ± 38.1 .036 .034 Phasic EMG activity in mentalis (%) 35.4 ± 19.4 26.5 ± 10.9 26.4 ± 16.0 .103 .069 Combined “any” EMG activity in mentalis with bilateral phasic BB (%) (n = 36)a 63.8 ± 31.4 (n = 11) 54.9 ± 20.2 (n = 16) 42.3 ± 34.0 (n = 7) .377 .238 BB = biceps brachii; PD = Parkinson disease; DLB = dementia with Lewy bodies; MCI = mild cognitive impairment; EMG = electromyography. Values are expressed as mean ± standard deviation. aTwo patients were diagnosed with multiple system atrophy and are not shown in the table. Open in new tab Table 5 EMG Activity in Each Type of Emerging Disease. PD (n = 15) DLB (n = 19) MCI (n = 13) p (PD vs. DLB) p (PD vs. DLB + MCI) Tonic EMG activity in mentalis (%) 48.2 ± 36.5a 24.6 ± 25.4 27.2 ± 38.1 .036 .034 Phasic EMG activity in mentalis (%) 35.4 ± 19.4 26.5 ± 10.9 26.4 ± 16.0 .103 .069 Combined “any” EMG activity in mentalis with bilateral phasic BB (%) (n = 36)a 63.8 ± 31.4 (n = 11) 54.9 ± 20.2 (n = 16) 42.3 ± 34.0 (n = 7) .377 .238 PD (n = 15) DLB (n = 19) MCI (n = 13) p (PD vs. DLB) p (PD vs. DLB + MCI) Tonic EMG activity in mentalis (%) 48.2 ± 36.5a 24.6 ± 25.4 27.2 ± 38.1 .036 .034 Phasic EMG activity in mentalis (%) 35.4 ± 19.4 26.5 ± 10.9 26.4 ± 16.0 .103 .069 Combined “any” EMG activity in mentalis with bilateral phasic BB (%) (n = 36)a 63.8 ± 31.4 (n = 11) 54.9 ± 20.2 (n = 16) 42.3 ± 34.0 (n = 7) .377 .238 BB = biceps brachii; PD = Parkinson disease; DLB = dementia with Lewy bodies; MCI = mild cognitive impairment; EMG = electromyography. Values are expressed as mean ± standard deviation. aTwo patients were diagnosed with multiple system atrophy and are not shown in the table. Open in new tab DISCUSSION We have shown in this study including patients with IRBD who later develop a clinically defined neurodegenerative syndrome that the EMG recording of the upper limbs in addition to the mentalis muscle is important for the correct identification of IRBD. If we had only used the mentalis we would have missed 18.4% of true IRBD patients. Our results support the concept that recording upper limb muscles increases the ability to identify IRBD by V-PSG. This may be in part due to the fact that the mentalis do not detect epochs when the patient displays abnormal behaviors involving only the limbs and not the head, which is a common situation in RBD.11 A previous study showed that isolated recording of the mentalis does not capture 35.5% of the behavioral events seen or heard on video while simultaneous recording of mentalis, right and left FDS only misses 4.6% of 3-second miniepochs containing motor events or vocalizations.19 The EMG quantification of combined upper limbs and mentalis muscles, as proposed by the SINBAR group,10,11 would have missed four (8.2%) IRBD patients. These four patients would have not been qualified as having “excessive” EMG activity during REM sleep in any of the two EMG montages. In these four cases visualization of abnormal behaviors typical of RBD with synchronized audiovisual recording was determinant for making the diagnosis of IRBD. This finding indicates that identification in REM sleep of behavioral abnormalities typical of RBD by audiovisual analysis in V-PSG is essential for the diagnosis of IRBD. Abnormally increased EMG activity in the mentalis (both phasic and tonic) is considered an essential requirement in the diagnosis of RBD.2 In our study, however, there were patients who later developed a defined neurodegenerative syndrome that clearly had very low levels of mentalis EMG activity and even in five cases tonic EMG activity was absent in any of the REM epochs analyzed. Several factors can account for this observation. First, we cannot exclude that the rates of muscular activity in these subjects could be higher if a second V-PSG night would have been recorded (intra-individual night to night variability). Second, methodological aspects in the quantification of EMG activity may also be responsible of these variabilities (eg, using two or four times the background amplitude; using 2 or 3-second miniepochs for quantifying phasic activity; using 20 vs. 30-second epochs9,10; having an absolute amplitude criteria; or differences in defining the background for the tonic activity).9–11,20,21 Finally, it is also possible that there are true IRBD patients with a different profiles showing low amounts of EMG activity in the mentalis during REM sleep. In fact, seven of the nine patients who had EMG activity below the cut-offs for the mentalis were later diagnosed with cognitive impairment (MCI or DLB). We have found in this study that IRBD patients who developed PD had higher amounts of tonic EMG activity in the mentalis than those who developed DLB or MCI. In line with this finding, another study20 reported that IRBD patients converting to PD had higher rates of tonic EMG activity in the mentalis than patients remaining disease-free. Strengths of our study are the inclusion of a homogeneous group of subjects with IRBD who later developed a defined neurodegenerative syndrome, the fact that the scorer was blind to the condition of the subjects, that we included a detailed analysis of the audiovisual recordings, and that we excluded individuals who were treated with medications capable to modify the quantity of muscular activity during REM sleep. A possible limitation of this study was the inclusion of patients with mild to moderate sleep apnea. It is unknown if an elevated index of respiratory events interferes with the analysis of EMG activity after arousals and respiratory-related EMG increases in the mentalis were carefully excluded from the measurements.9,22 Although the presence of apneic events during REM sleep might decrease the number of 30-second epochs and 3-second miniepochs available for analysis, we did not find, however, differences in the duration of the REM sleep between patients with apneic events and those without them. Also, we cannot fully exclude that the evaluation of the FDS instead of the BB could have produced higher rates of EMG activity and reduce the number of false negatives, since all 13 patients evaluated with the FDS had values above the cut-offs. In summary, this is the first study comparing two different manual EMG methods for the diagnosis of IRBD analyzing patients who eventually developed a clinical defined neurodegenerative syndrome. We have been able to show that measurement of EMG activity in the upper limbs combined with the mentalis when compared with the isolated measurement of the mentalis increases the ability to diagnose IRBD. In addition, we found that detection with V-PSG of abnormal motor and vocal events during REM sleep in a patient with a history of dream-enacting behaviors is determinant to perform the diagnosis of IRBD, particularly in those few cases with low levels of EMG activity in REM sleep. DISCLOSURE STATEMENT None declared. REFERENCES 1. Schenck CH Bundlie SR Ettinger MG Mahowald MW . Chronic behavioral disorders of human REM sleep: a new category of parasomnia . Sleep . 1986 ; 9 ( 2 ): 293 – 308 . Google Scholar Crossref Search ADS PubMed WorldCat 2. American Academy of Sleep Medicine . International Classification of Sleep Disorders . 3rd ed. Darien, IL : American Academy of Sleep Medicine ; 2014 . WorldCat COPAC 3. Iranzo A Santamaria J Tolosa E . Idiopathic rapid eye movement sleep behaviour disorder: diagnosis, management, and the need for neuroprotective interventions . Lancet Neurol . 2016 ; 15 ( 4 ): 405 – 419 . Google Scholar Crossref Search ADS PubMed WorldCat 4. Schenck CH Boeve BF Mahowald MW . Delayed emergence of a parkinsonian disorder or dementia in 81% of older men initially diagnosed with idiopathic rapid eye movement sleep behavior disorder: a 16-year update on a previously reported series . Sleep Med . 2013 ; 14 ( 8 ): 744 – 748 . Google Scholar Crossref Search ADS PubMed WorldCat 5. Iranzo A Molinuevo JL Santamaría J et al. . Rapid-eye-movement sleep behaviour disorder as an early marker for a neurodegenerative disorder: a descriptive study . Lancet Neurol . 2006 ; 5 ( 7 ): 572 – 577 . Google Scholar Crossref Search ADS PubMed WorldCat 6. Postuma RB Gagnon JF Vendette M Fantini ML Massicotte-Marquez J Montplaisir J . Quantifying the risk of neurodegenerative disease in idiopathic REM sleep behavior disorder . Neurology . 2009 ; 72 ( 15 ): 1296 – 1300 . Google Scholar Crossref Search ADS PubMed WorldCat 7. Iranzo A Tolosa E Gelpi E et al. . Neurodegenerative disease status and post-mortem pathology in idiopathic rapid-eye-movement sleep behaviour disorder: an observational cohort study . Lancet Neurol . 2013 ; 12 ( 5 ): 443 – 453 . Google Scholar Crossref Search ADS PubMed WorldCat 8. Consens FB Chervin RD Koeppe RA et al. . Validation of a polysomnographic score for REM sleep behavior disorder . Sleep . 2005 ; 28 ( 8 ): 993 – 997 . Google Scholar Crossref Search ADS PubMed WorldCat 9. Montplaisir J Gagnon JF Fantini ML et al. . Polysomnographic diagnosis of idiopathic REM sleep behavior disorder . Mov Disord . 2010 ; 25 ( 13 ): 2044 – 2051 . Google Scholar Crossref Search ADS PubMed WorldCat 10. Frauscher B Iranzo A Gaig C et al. .; SINBAR (Sleep Innsbruck Barcelona) Group . Normative EMG values during REM sleep for the diagnosis of REM sleep behavior disorder . Sleep . 2012 ; 35 ( 6 ): 835 – 847 . Google Scholar Crossref Search ADS PubMed WorldCat 11. Frauscher B Iranzo A Högl B et al. .; SINBAR (Sleep Innsbruck Barcelona group) . Quantification of electromyographic activity during REM sleep in multiple muscles in REM sleep behavior disorder . Sleep . 2008 ; 31 ( 5 ): 724 – 731 . Google Scholar Crossref Search ADS PubMed WorldCat 12. Iber C. Ancoli-Israel S Chesson A Quan SF. AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications . 1st ed. Westchester, IL : American Academy of Sleep Medicine ; 2007 . Google Preview WorldCat COPAC 13. Ferri R Cosentino FI Pizza F Aricò D Plazzi G . The timing between REM sleep behavior disorder and Parkinson’s disease . Sleep Breath . 2014 ; 18 ( 2 ): 319 – 323 . Google Scholar Crossref Search ADS PubMed WorldCat 14. Hughes AJ Daniel SE Kilford L Lees AJ . Accuracy of clinical diagnosis of idiopathic Parkinson’s disease: a clinico-pathological study of 100 cases . J Neurol Neurosurg Psychiatry . 1992 ; 55 ( 3 ): 181 – 184 . Google Scholar Crossref Search ADS PubMed WorldCat 15. McKeith IG Dickson DW Lowe J et al. .; Consortium on DLB . Diagnosis and management of dementia with Lewy bodies: third report of the DLB Consortium . Neurology . 2005 ; 65 ( 12 ): 1863 – 1872 . Google Scholar Crossref Search ADS PubMed WorldCat 16. Gilman S Wenning GK Low PA et al. . Second consensus statement on the diagnosis of multiple system atrophy . Neurology . 2008 ; 71 ( 9 ): 670 – 676 . Google Scholar Crossref Search ADS PubMed WorldCat 17. Petersen RC . Mild cognitive impairment as a diagnostic entity . J Intern Med . 2004 ; 256 ( 3 ): 183 – 194 . Google Scholar Crossref Search ADS PubMed WorldCat 18. Kumru H Santamaria J Tolosa E et al. . Rapid eye movement sleep behavior disorder in parkinsonism with parkin mutations . Ann Neurol . 2004 ; 56 ( 4 ): 599 – 603 . Google Scholar Crossref Search ADS PubMed WorldCat 19. Iranzo A Frauscher B Santos H et al. .; SINBAR (Sleep Innsbruck Barcelona) Group . Usefulness of the SINBAR electromyographic montage to detect the motor and vocal manifestations occurring in REM sleep behavior disorder . Sleep Med . 2011 ; 12 ( 3 ): 284 – 288 . Google Scholar Crossref Search ADS PubMed WorldCat 20. Postuma RB Gagnon JF Rompré S Montplaisir JY . Severity of REM atonia loss in idiopathic REM sleep behavior disorder predicts Parkinson disease . Neurology . 2010 ; 74 ( 3 ): 239 – 244 . Google Scholar Crossref Search ADS PubMed WorldCat 21. Lee SA Kim CS Cho CU Kim B Lee GH . Quantitative EMG criteria for diagnosing idiopathic REM sleep behavior disorder . Sleep Breath . 2015 ; 19 ( 2 ): 685 – 691 . Google Scholar Crossref Search ADS PubMed WorldCat 22. McCarter SJ St Louis EK Duwell EJ et al. . Diagnostic thresholds for quantitative REM sleep phasic burst duration, phasic and tonic muscle activity, and REM atonia index in REM sleep behavior disorder with and without comorbid obstructive sleep apnea . Sleep . 2014 ; 37 ( 10 ): 1649 – 1662 . Google Scholar Crossref Search ADS PubMed WorldCat Author notes Address correspondence to: Joan Santamaria, Neurology Service, Hospital Clinic de Barcelona, C/ Villarroel 170, Barcelona 08036, Spain. Telephone: 3493-227-5413; Fax: 3493-227-5783; Email: [email protected] © Sleep Research Society 2017. Published by Oxford University Press on behalf of the Sleep Research Society. All rights reserved. For permissions, please e-mail [email protected]. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png SLEEP Oxford University Press

Diagnostic Value of Isolated Mentalis Versus Mentalis Plus Upper Limb Electromyography in Idiopathic REM Sleep Behavior Disorder Patients Eventually Developing a Neurodegenerative Syndrome

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Oxford University Press
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© Sleep Research Society 2017. Published by Oxford University Press on behalf of the Sleep Research Society. All rights reserved. For permissions, please e-mail [email protected].
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0161-8105
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10.1093/sleep/zsx025
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Abstract

Abstract Study Objectives: To compare two electromyographic (EMG) montages, isolated mentalis muscle versus mentalis in combination with upper limb muscles in the baseline diagnostic video-polysomnography (V-PSG) of patients with idiopathic REM sleep behaviors disorder (IRBD) who eventually were diagnosed with a clinically defined neurodegenerative syndrome. Methods: Forty-nine patients were included. At baseline, diagnosis of RBD was based on a typical history of dream enactment behaviors plus V-PSG showing REM sleep with qualitative increased EMG activity and/or abnormal behaviors. Quantification of EMG activity (tonic, phasic and “any”) in the mentalis and upper limb muscles (biceps brachii-BB, n = 36 or flexor digitorum superficialis-FDS, n = 13) was performed manually and compared with published cut-offs. Results: Nine (18.4%) patients had either tonic or phasic EMG below the cut-offs for the isolated mentalis and four of them (11.1 %) also had values below the cut-off for the mentalis combined with BB. All 13 patients recorded with the FDS were above the mentalis combined with FDS cut-off. For the diagnosis of IRBD, sensitivity of isolated mentalis was 81.6% and of the combination of mentalis plus upper limb muscles was 91.8% (p = .03). Audiovisual analysis showed abnormal REM sleep behaviors in all nine patients with values below the cut-offs. Conclusion: Quantification of EMG activity in the upper limbs combined with the mentalis increases the ability to diagnose IRBD when compared with the isolated measurement of the mentalis. Detection of typical abnormal behaviors during REM sleep with audiovisual analysis is essential for the diagnosis of IRBD in patients with EMG values below the published cut-offs. Idiopathic REM sleep behavior disorder, electromyographic quantification, mentalis, upper limbs, flexor digitorum superficialis, biceps brachii. Statement of Significance A correct diagnosis of idiopathic REM sleep behavior disorder (IRBD) is crucial because it carries a high risk of a neurodegenerative disease. Our study compares two currently used electromyographic montages, isolated mentalis versus mentalis combined with upper limb muscles in the baseline video-polysomnogram of IRBD patients who later developed a neurodegenerative syndrome. We found that the montage of mentalis combined with upper limbs identifies best patients with IRBD. However, video-recording of abnormal behaviors in REM sleep is essential to diagnose the condition in a small subset of patients with EMG values within the normal range. These findings are relevant to increase the diagnostic accuracy of IRBD while using video-polysomnography. INTRODUCTION REM sleep behavior disorder (RBD) is a parasomnia characterized by nightmares and repeated episodes of abnormal movements and vocalizations during REM sleep.1–3 An accurate diagnosis of RBD is particularly important in idiopathic RBD (IRBD) because the parasomnia usually heralds a defined neurodegenerative syndrome such as mild cognitive impairment (MCI), dementia with Lewy bodies (DLB), Parkinson disease (PD) or more rarely multiple system atrophy (MSA).4–7 Video-polysomnography (V-PSG) showing excessive amounts of sustained (tonic) or intermittent (phasic) electromyographic (EMG) activity during REM sleep is required for the diagnosis of RBD.2 The definition of what constitutes “excessive” EMG activity and the body muscles where it should be measured have been the focus of several studies.8–11 For the diagnosis of IRBD, quantification of EMG activity exclusively in the mentalis muscle is a common practice in many sleep centers since this muscle is routinely used for sleep scoring.12 Isolated quantification of EMG activity of the mentalis has good discriminative power8–10 and cut-off levels of 30% for tonic and 15% for phasic EMG activity have been proposed for the correct identification of IRBD.9 EMG recording of the mentalis, however, is prone to include breathing and snoring artifacts and may be atonic in epochs in which abnormal behaviors typical of RBD occur only in the limbs.10,11 Therefore, investigators have examined additional muscles for the diagnosis of IRBD.11 The anterior tibialis has low discriminative power because this muscle in healthy people often shows benign distal movements which are not specific for RBD.9,10 In contrast, EMG activity in upper limb muscles, such as the flexor digitorum superficialis (FDS) or the biceps brachii (BB), in addition to the mentalis, has a high discriminative power11 when using cut-off levels of 31.9% and 21.8%, respectively.10 It is currently unclear which method of quantification is preferable to diagnose IRBD. Ideally, the optimal system would be the one that best identifies patients with IRBD. However, since there is not an independent marker or a gold standard for diagnosis of IRBD other than V-PSG, there is some circularity in this issue: only subjects with high amounts of EMG activity in REM sleep are diagnosed with IRBD, whereas those with lower amounts (but displaying some typical RBD manifestations in REM sleep) may not be diagnosed with the condition. For instance, one study using EMG quantification9 only in the mentalis found values within normal range in 11.8% of subjects diagnosed with IRBD using clinical history. Other studies have also found some overlap in the values of EMG activity between patients and controls.10,13 These observations indicate that there are patients with a clinical picture highly suggestive of IRBD that have EMG values within the proposed normal range of EMG activity during REM sleep. One way to overcome these difficulties is to study patients that were diagnosed initially with IRBD and eventually developed a defined neurodegenerative syndrome. Since IRBD in those patients was “per se” an early manifestation of the underlying disease, it is reasonable to assume that their clinical picture corresponded to “true” IRBD, no matter the quantity of EMG activity found in the baseline V-PSG study. The aim of this study was to compare quantitative EMG measures between the isolated mentalis and the combination of the mentalis with upper limb muscles in the baseline diagnostic V-PSG of IRBD patients who later developed a defined neurodegenerative syndrome. This would elucidate which EMG montage in PSG is more adequate for the diagnosis of IRBD. METHODS Patient Selection We selected all patients who were diagnosed with IRBD at the Hospital Clinic de Barcelona, Barcelona, Spain, from January 2000 to June 2015. Diagnosis of IRBD in our center required: (1) clinical history of dream-enacting behaviors; (2) V-PSG showing REM sleep with qualitative increased EMG activity and/or abnormal movements/behaviors in REM sleep; and (3) and absence of a defined neurodegenerative syndrome. We did not establish a minimal amount of EMG activity in REM sleep if clear dream-enactment behaviors typical of RBD (eg, prominent body jerking, punching, kicking, shouting) were detected during REM sleep in the videotape analysis. When the diagnosis of IRBD was made, patients were clinically followed-up as previously described.5 We identified 49 patients who developed a clinically defined neurodegenerative syndrome disease (PD, DLB, MCI or MSA) according to current criteria.14–17 In order for the scorer of EMG activity not to be influenced by the knowledge that the patients were diagnosed with a defined neurodegenerative syndrome, V-PSG studies from IRBD patients with similar age and gender distribution who remained disease-free after at least 5 years of follow-up (n = 36) were also quantified. All the studies were anonymized and the scorer was blind for the outcome (converted to a defined neurodegenerative syndrome or remained disease-free). The results of EMG quantification of the patients who remained disease-free were not used in this study. Exclusion criteria were treatment with antidepressants, melatonin and benzodiazepines (including clonazepam) at the time of the baseline V-PSG, and technical artifacts preventing proper EMG quantification. We did not exclude patients that showed mild to moderate obstructive sleep apnea in V-PSG but we carefully excluded from quantification all REM sleep epochs with respiratory-related EMG increases (regular breathing, snoring or apnea/hypopnea-induced arousals). The ethics committee of Hospital Clinic of Barcelona approved this study. Polysomnographic Variables All patients underwent a full-night PSG study with synchronized audiovisual recording with a digital polygraph (Deltamed, software version 1998, Paris, France). V-PSG included electroencephalogram (EEG) (C3, C4, O1, and O2, referred to the contralateral ear; F3 and F4 were added in 2007), right and left electro-oculograms, surface mentalis EMG and right and left anterior tibialis EMG. From 2000 to 2007 we recorded upper limb EMG activity from right and left BB, and in the right and left FDS from 2007 to 2015.11 V-PSG also included electrocardiogram, nasal and oral air-flow assessment, thoracic and abdominal movement assessment, body position and measurement of oxyhemoglobin saturation. Sleep stages were scored according to American Academy of Sleep Medicine12 criteria with allowance to score REM sleep despite excessive EMG activity in the mentalis muscle channel. The occurrence of the first rapid eye movement was used to determine the onset of a REM sleep stage. The end of a REM sleep stage was determined when either no REMs were detected in three consecutive minutes or an awakening, K complex, or spindles were observed.12 A new REM sleep stage was considered when it occurred 30 minutes after the previous episode. Analysis of EMG Activity In each V-PSG study, quantification of tonic, phasic, and “any” (either tonic or phasic) EMG activity was performed manually during REM sleep. EMG activity in REM sleep was quantified using 30-second epochs and 3-second miniepochs. All movement artifacts and increases in EMG tone due to arousals were excluded from analysis. A trained sleep scorer (AF) who was blinded to the patient’s outcome (converted to a defined neurodegenerative syndrome or remained disease-free) performed the EMG quantification. In doubtful cases, the recordings were reviewed and discussed with the rest of the team until agreement was reached. The EMG activity was analyzed in all channels using a sampling rate of 256 Hz, a low-frequency filter at 10 Hz, high-frequency filter at 100 Hz, and a display sensitivity of 5 μV/mm. Impedances of surface EMG electrodes had to be lower than 10 kΩ. Tonic EMG activity was scored only in the mentalis muscle channel using 30-second epochs with a display sensitivity of 5 μV/mm although in case of doubt a 3 μV/mm display and/or a ruler were used to better discriminate the signal amplitude. The reference background EMG signal was the lowest one recorded in the same REM sleep stage analyzed, or if continuous EMG activity in REM sleep occurred, the one recorded in the most stable and relaxed adjacent previous NREM sleep epochs. Each epoch was scored as “tonic” in the mentalis when the increased sustained EMG activity was present in more than 50% of the total 30-second epoch duration with an amplitude of at least twice the background EMG activity or more than 10 µV. The periods of PSG shorter than a full 30-second epoch of sleep, mainly occurring at the end of each REM sleep stage, were not included in the analysis. The rate of tonic EMG activity was calculated as the number of 30-second epochs with this EMG activity divided by the whole number of 30-second epochs during REM sleep. Phasic EMG activity of three muscles (mentalis and either right and left BB or right and left FDS) was quantified during REM sleep. Each EMG channel was displayed isolated on the computer screen and scored independently from the other muscles. After the scoring of a muscle was completed, the process was repeated in the remaining two muscles. Phasic EMG events were defined as any burst of EMG activity lasting 0.1–5 seconds with an amplitude exceeding twice the background EMG activity during REM sleep. Each 3-second miniepoch in each EMG channel was scored as “0” when phasic EMG activity was absent and “1” when phasic EMG activity was present. Three-second miniepochs were also scored as having or not having “any” EMG activity, irrespective of whether it contained tonic, phasic or a combination of both types of EMG activity in the mentalis. The rates of phasic and “any” EMG activity in the mentalis were calculated as the proportion of 3-second miniepochs during REM sleep containing the corresponding type of muscle activity. In the upper limbs only phasic EMG activity was quantified and the proportion of 3-second miniepochs during REM sleep containing this type of EMG activity was calculated. In addition, we scored the rates of “any” EMG activity in the mentalis associated with phasic EMG activity in the right and left upper limbs. In this EMG montage a 3-second miniepoch was computed as having EMG activity when at least one of the three muscles evaluated had EMG activity (at least one score of “1”), and as not having EMG activity when none of the muscles in the combination had “any” or phasic EMG activity measure. Classification of Patients According to Different Cut-Offs and Emerging Disease We identified the number of patients with EMG activity rates below previously published cut-offs for IRBD diagnosis. For the isolated mentalis muscle we used the cut-off of ≥30% for tonic EMG activity or ≥15% for phasic EMG activity, as reference, as previously published.9 For the combination of mentalis plus upper limb muscles we used the cut-off of ≥31.9% for “any” EMG activity in the mentalis with the right and left FDS (SINBAR montage) and of ≥21.8 % for “any” mentalis with the right and left BB.10 Video Analysis When EMG measurements during REM sleep did not reach the previously published proposed cut-offs, we reviewed the video tapes of the same V-PSG studies to see if they contained the typical abnormal movements, behaviors and vocalizations displayed by patients with IRBD during REM sleep. Visual analysis was performed in conjunction with the PSG recording and the excluded epochs (due to respiratory events, eg,) during the quantification were also excluded from the video analysis. The intensity of these manifestations was classified as mild, moderate or severe according to a system previously described in our center.18 Statistical Analysis Descriptive demographic, clinical and PSG data are given as mean ± standard deviations, counts and frequencies. Comparison of demographic variables between the group of patients who developed a defined a neurodegenerative syndrome and those who remained idiopathic was done with a chi square test and T-Student, as appropriated. Comparison of rates of EMG activity between the different defined neurodegenerative syndromes was performed with T-Student. Since sensitivity of mentalis combined with upper limb muscles should ever be equal or greater than the mentalis alone, comparison of sensitivities was done with unilateral binomial tests. SPSS 19 for Windows (SPSS, Inc., Chicago, IL) was used for all statistical analyses. RESULTS Demographic, Clinical, and PSG Data We studied 49 patients (43 men) with IRBD who later were diagnosed with a clinically defined neurodegenerative syndrome (15 PD, 19 DLB, 2 MSA and 13 MCI) at the age of 73.6 ± 5.1 (range, 60–85) years and after a mean follow-up of 4.7 ± 3.1 years. Mean age at diagnosis of IRBD was 68.6 ± 5.3 years. There were no significant differences in demographic variables between patients who developed a clinically defined neurodegenerative syndrome and those who remained disease-free (Table 1). Table 1 Demographic Characteristics of IRBD Patients Who Developed a Clinically Defined Neurodegenerative Syndrome and Those Who Remained Idiopathic. Demographic variables N Not remained idiopathic Remained idiopathic p 49 36 Sex, male (n, %) 43 (87.8%) 26 (72.2%) .070 Age at estimated IRBD onset (years) 62.1 ± 5.6 61.5 ± 8.3 .702 (range, 50–73) (range, 44–77) Interval from estimated IRBD onset to diagnosis of IRBD by V-PSG (years) 6.5 ± 5.5 5.1 ± 4.2 .192 (range, 1–25) (range, 1–20) Age at IRBD diagnosis (years) 68.6 ± 5.3 66.7 ± 7.4 .157 (range, 56–78) (range, 49–79) Follow-up (years)a 4.7 ± 3.1 7.9 ± 2.12 .001 (range, 0.5–12) (range, 5–13) Demographic variables N Not remained idiopathic Remained idiopathic p 49 36 Sex, male (n, %) 43 (87.8%) 26 (72.2%) .070 Age at estimated IRBD onset (years) 62.1 ± 5.6 61.5 ± 8.3 .702 (range, 50–73) (range, 44–77) Interval from estimated IRBD onset to diagnosis of IRBD by V-PSG (years) 6.5 ± 5.5 5.1 ± 4.2 .192 (range, 1–25) (range, 1–20) Age at IRBD diagnosis (years) 68.6 ± 5.3 66.7 ± 7.4 .157 (range, 56–78) (range, 49–79) Follow-up (years)a 4.7 ± 3.1 7.9 ± 2.12 .001 (range, 0.5–12) (range, 5–13) IRBD = idiopathic REM sleep behavior disorder; V-PSG = video-polysomnography. Values are expressed as mean ± standard deviation and range, frequency and percentage. V-PSG: polysomnography with audiovisual recording. aInterval from diagnosis of IRBD in our sleep center to diagnosis of a clinically defined neurodegenerative syndrome or to the last visit in those subjects who remained idiopathic. Open in new tab Table 1 Demographic Characteristics of IRBD Patients Who Developed a Clinically Defined Neurodegenerative Syndrome and Those Who Remained Idiopathic. Demographic variables N Not remained idiopathic Remained idiopathic p 49 36 Sex, male (n, %) 43 (87.8%) 26 (72.2%) .070 Age at estimated IRBD onset (years) 62.1 ± 5.6 61.5 ± 8.3 .702 (range, 50–73) (range, 44–77) Interval from estimated IRBD onset to diagnosis of IRBD by V-PSG (years) 6.5 ± 5.5 5.1 ± 4.2 .192 (range, 1–25) (range, 1–20) Age at IRBD diagnosis (years) 68.6 ± 5.3 66.7 ± 7.4 .157 (range, 56–78) (range, 49–79) Follow-up (years)a 4.7 ± 3.1 7.9 ± 2.12 .001 (range, 0.5–12) (range, 5–13) Demographic variables N Not remained idiopathic Remained idiopathic p 49 36 Sex, male (n, %) 43 (87.8%) 26 (72.2%) .070 Age at estimated IRBD onset (years) 62.1 ± 5.6 61.5 ± 8.3 .702 (range, 50–73) (range, 44–77) Interval from estimated IRBD onset to diagnosis of IRBD by V-PSG (years) 6.5 ± 5.5 5.1 ± 4.2 .192 (range, 1–25) (range, 1–20) Age at IRBD diagnosis (years) 68.6 ± 5.3 66.7 ± 7.4 .157 (range, 56–78) (range, 49–79) Follow-up (years)a 4.7 ± 3.1 7.9 ± 2.12 .001 (range, 0.5–12) (range, 5–13) IRBD = idiopathic REM sleep behavior disorder; V-PSG = video-polysomnography. Values are expressed as mean ± standard deviation and range, frequency and percentage. V-PSG: polysomnography with audiovisual recording. aInterval from diagnosis of IRBD in our sleep center to diagnosis of a clinically defined neurodegenerative syndrome or to the last visit in those subjects who remained idiopathic. Open in new tab Polysomnographic data are shown in Table 2. A mean of 89.1 ± 42.9 epochs and 964.0 ± 444.6 3-second miniepochs of REM sleep were analyzed. The mean apnea/hypoapnea index (AHI) was 14.7 ± 16.2. Twenty-eight (57.1%) patients had AHI lower than 10. Six of these 28 were previously diagnosed with obstructive sleep apnea syndrome, were effectively treated with continuous positive airway pressure and wore the mask during their diagnostic V-PSG. Sixteen patients (32.6%) had an AHI greater than 15. Five of these 16 patients had apneas and hypopneas exclusively related to the supine position but REM sleep was recorded in the lateral position not containing respiratory-related arousals. Eleven (22.4%) patients had an AHI greater than 15 with a mean AHI during REM sleep of 32.5 ± 14.7 (range, 17.8–62.7). In these 11 patients, we carefully excluded from EMG analysis the 30-second epochs and 3-second miniepochs containing respiratory related arousals or awakenings. The excluded epochs were 37.0 ± 18.9 % of the total epochs in REM sleep leaving 82.6 ± 24.5 epochs for analysis. The number of scored 30-second epochs and 3-second miniepochs was similar in the group of 11 patients with apneic events during REM sleep and the 38 remaining patients (82.6 ± 24.5 vs. 91.0 ± 47.0, p = .576 and 910.4 ± 247.2 vs. 979.5 ± 488.7, p = .655, respectively). Table 2 Polysomnographic Variables of the 49 Patients With IRBD Who Eventually Developed a Clinically Defined Neurodegenerative Syndrome. Time in bed, min 464.5 ± 42.8 Total sleep time, min 345.3 ± 62.9 Sleep efficiency, % 74.4 ± 12.0 Wake after sleep onset, min 95.2 ± 58.0 Sleep stage, %  N1 22.3 ± 11.4  N2 44.0 ± 9.4  N3 15.1 ± 10.1  REM 15.6 ± 7.3 Sleep-onset latency, min 21.5 ± 14.1 REM sleep latency, min 114.7 ± 80.4 REM sleep stages, n 2.8 ± 1.0 30-s epochs, n 89.1 ± 42.9 3-s miniepochs, n 964.0 ± 444.6 AHI index 14.7 ± 16.2 PLMS index 18.7 ± 25.9 Time in bed, min 464.5 ± 42.8 Total sleep time, min 345.3 ± 62.9 Sleep efficiency, % 74.4 ± 12.0 Wake after sleep onset, min 95.2 ± 58.0 Sleep stage, %  N1 22.3 ± 11.4  N2 44.0 ± 9.4  N3 15.1 ± 10.1  REM 15.6 ± 7.3 Sleep-onset latency, min 21.5 ± 14.1 REM sleep latency, min 114.7 ± 80.4 REM sleep stages, n 2.8 ± 1.0 30-s epochs, n 89.1 ± 42.9 3-s miniepochs, n 964.0 ± 444.6 AHI index 14.7 ± 16.2 PLMS index 18.7 ± 25.9 AHI = apnea-hypoapnea index (number of apneas and hypoapneas per hour of sleep); IRBD = idiopathic REM sleep behavior disorder; PLMS index = periodic leg movements in sleep (number of periodic leg movements in sleep per hour of sleep); REM = rapid eye movement. Values are expressed as mean ± standard deviation. Open in new tab Table 2 Polysomnographic Variables of the 49 Patients With IRBD Who Eventually Developed a Clinically Defined Neurodegenerative Syndrome. Time in bed, min 464.5 ± 42.8 Total sleep time, min 345.3 ± 62.9 Sleep efficiency, % 74.4 ± 12.0 Wake after sleep onset, min 95.2 ± 58.0 Sleep stage, %  N1 22.3 ± 11.4  N2 44.0 ± 9.4  N3 15.1 ± 10.1  REM 15.6 ± 7.3 Sleep-onset latency, min 21.5 ± 14.1 REM sleep latency, min 114.7 ± 80.4 REM sleep stages, n 2.8 ± 1.0 30-s epochs, n 89.1 ± 42.9 3-s miniepochs, n 964.0 ± 444.6 AHI index 14.7 ± 16.2 PLMS index 18.7 ± 25.9 Time in bed, min 464.5 ± 42.8 Total sleep time, min 345.3 ± 62.9 Sleep efficiency, % 74.4 ± 12.0 Wake after sleep onset, min 95.2 ± 58.0 Sleep stage, %  N1 22.3 ± 11.4  N2 44.0 ± 9.4  N3 15.1 ± 10.1  REM 15.6 ± 7.3 Sleep-onset latency, min 21.5 ± 14.1 REM sleep latency, min 114.7 ± 80.4 REM sleep stages, n 2.8 ± 1.0 30-s epochs, n 89.1 ± 42.9 3-s miniepochs, n 964.0 ± 444.6 AHI index 14.7 ± 16.2 PLMS index 18.7 ± 25.9 AHI = apnea-hypoapnea index (number of apneas and hypoapneas per hour of sleep); IRBD = idiopathic REM sleep behavior disorder; PLMS index = periodic leg movements in sleep (number of periodic leg movements in sleep per hour of sleep); REM = rapid eye movement. Values are expressed as mean ± standard deviation. Open in new tab Quantification of EMG Activity and Audiovisual Analysis Rates of tonic, phasic and “any” EMG activity in individual and combined muscles are shown in Table 3. Table 3 Electromyographic Activity of the 49 Patients Who Eventually Developed a Clinically Defined Neurodegenerative Syndrome. Muscle Tonic EMG activity in the mentalis (%) 33.8 ± 33.8 (0–95.9) Phasic EMG activity in the mentalis (%) 29.2 ± 15.3 (8.2–74.9) “Any” EMG activity in the mentalis (%) 49.5 ± 28.1 (8.2–93.0) Combined “any” EMG activity in the mentalis with bilateral phasic BB (%) (n = 36) 56.2 ± 27.2 (8.9–94.7) Combined “any” EMG activity in the mentalis with bilateral phasic FDS (%) (n = 13) 67.4 ± 20.1 (37.8–96.3) Phasic EMG activity in the right BB (n = 36) 17.2 ± 13.3 (1.3–52.3) Phasic EMG activity in the left BB (n = 36) 17.0 ± 15.0 (0.5–56.3) Phasic EMG activity in right FDS (%) (n = 13) 19.6 ± 13.7 (2.4–51.7) Phasic EMG activity in left FDS (%) (n = 13) 20.3 ± 11.3 (4.4–41.3) Muscle Tonic EMG activity in the mentalis (%) 33.8 ± 33.8 (0–95.9) Phasic EMG activity in the mentalis (%) 29.2 ± 15.3 (8.2–74.9) “Any” EMG activity in the mentalis (%) 49.5 ± 28.1 (8.2–93.0) Combined “any” EMG activity in the mentalis with bilateral phasic BB (%) (n = 36) 56.2 ± 27.2 (8.9–94.7) Combined “any” EMG activity in the mentalis with bilateral phasic FDS (%) (n = 13) 67.4 ± 20.1 (37.8–96.3) Phasic EMG activity in the right BB (n = 36) 17.2 ± 13.3 (1.3–52.3) Phasic EMG activity in the left BB (n = 36) 17.0 ± 15.0 (0.5–56.3) Phasic EMG activity in right FDS (%) (n = 13) 19.6 ± 13.7 (2.4–51.7) Phasic EMG activity in left FDS (%) (n = 13) 20.3 ± 11.3 (4.4–41.3) BB = biceps brachii; EMG = electromyography; FDS = flexor digitorum superficialis.Values are expressed as mean ± standard deviation and range. Open in new tab Table 3 Electromyographic Activity of the 49 Patients Who Eventually Developed a Clinically Defined Neurodegenerative Syndrome. Muscle Tonic EMG activity in the mentalis (%) 33.8 ± 33.8 (0–95.9) Phasic EMG activity in the mentalis (%) 29.2 ± 15.3 (8.2–74.9) “Any” EMG activity in the mentalis (%) 49.5 ± 28.1 (8.2–93.0) Combined “any” EMG activity in the mentalis with bilateral phasic BB (%) (n = 36) 56.2 ± 27.2 (8.9–94.7) Combined “any” EMG activity in the mentalis with bilateral phasic FDS (%) (n = 13) 67.4 ± 20.1 (37.8–96.3) Phasic EMG activity in the right BB (n = 36) 17.2 ± 13.3 (1.3–52.3) Phasic EMG activity in the left BB (n = 36) 17.0 ± 15.0 (0.5–56.3) Phasic EMG activity in right FDS (%) (n = 13) 19.6 ± 13.7 (2.4–51.7) Phasic EMG activity in left FDS (%) (n = 13) 20.3 ± 11.3 (4.4–41.3) Muscle Tonic EMG activity in the mentalis (%) 33.8 ± 33.8 (0–95.9) Phasic EMG activity in the mentalis (%) 29.2 ± 15.3 (8.2–74.9) “Any” EMG activity in the mentalis (%) 49.5 ± 28.1 (8.2–93.0) Combined “any” EMG activity in the mentalis with bilateral phasic BB (%) (n = 36) 56.2 ± 27.2 (8.9–94.7) Combined “any” EMG activity in the mentalis with bilateral phasic FDS (%) (n = 13) 67.4 ± 20.1 (37.8–96.3) Phasic EMG activity in the right BB (n = 36) 17.2 ± 13.3 (1.3–52.3) Phasic EMG activity in the left BB (n = 36) 17.0 ± 15.0 (0.5–56.3) Phasic EMG activity in right FDS (%) (n = 13) 19.6 ± 13.7 (2.4–51.7) Phasic EMG activity in left FDS (%) (n = 13) 20.3 ± 11.3 (4.4–41.3) BB = biceps brachii; EMG = electromyography; FDS = flexor digitorum superficialis.Values are expressed as mean ± standard deviation and range. Open in new tab Twenty-seven (55.1%) patients did not reach the ≥30% cut-off for tonic EMG activity in the mentalis and nine of them had values below the 15% cut-off for phasic EMG activity. Therefore, nine (18.4%) patients had “normal” values of EMG activity in the mentalis (Figure 1, Table 4). Evaluation of the audiovisual recordings of these nine patients during REM sleep showed abnormal manifestations typical of RBD that were classified as mild in six patients, moderate in one and severe in two (Table 4). V-PSG also excluded RBD potential mimics (eg, severe obstructive sleep apnea, prominent periodic leg movements in sleep, NREM sleep parasomnias, nocturnal epilepsy) in these nine individuals. Figure 1 Open in new tabDownload slide Percentages of tonic EMG activity (1a) and phasic EMG activity (1b) in the mentalis of the 49 patients who eventually developed a clinically defined neurodegenerative syndrome (horizontal bar indicates the previously published proposed cut-off of 30% and 15% respectively).9 Figure 1 Open in new tabDownload slide Percentages of tonic EMG activity (1a) and phasic EMG activity (1b) in the mentalis of the 49 patients who eventually developed a clinically defined neurodegenerative syndrome (horizontal bar indicates the previously published proposed cut-off of 30% and 15% respectively).9 Table 4 Electromyographic Activity Measures and Audiovisual Findings in the Nine Patients Who Had Electromyographic Activity in the Mentalis Below the Proposed Cut-Offs for the Diagnosis of RBD. Patient Emerging condition Tonic EMG activity in the mentalis (%) Phasic EMG activity in the mentalis (%) “Any” EMG activity in the mentalis plus phasic EMG activity in upper limbs (%) Severity and types of abnormal manifestations typical of RBD detected in the audiovisual recordings during REM sleepa 1 DLB 21.6b 8.6b 48.8 (BB) Moderate (upper limbs elevation with jerks) 2 MCI 3.7b 13.6b 44.0 (FDS) Severe (lower limbs kicking) 3 PD 2.3b 12.1b 28.4 (BB) Mild (proximal four limbs jerking) 4 MCI 0b 10.6b 25.9 (BB) Mild (proximal four limbs jerking) 5 DLB 1.0b 14.4b 22.9 (BB) Mild (proximal four limbs jerking) 6 DLB 3.8b 10.9b 17.6b (BB) Mild (lower limbs jerking and repetitive hand movements) 7 MCI 1.4b 10.8b 15.0b (BB) Mild (sudden moderate trunk and four limbs jerking) 8 PD 2.8b 8.7b 13.5b (BB) Mild (proximal lower limbs jerking) 9 MCI 0b 8.2b 8.9b (BB) Severe (repetitive lower limbs kicking) Patient Emerging condition Tonic EMG activity in the mentalis (%) Phasic EMG activity in the mentalis (%) “Any” EMG activity in the mentalis plus phasic EMG activity in upper limbs (%) Severity and types of abnormal manifestations typical of RBD detected in the audiovisual recordings during REM sleepa 1 DLB 21.6b 8.6b 48.8 (BB) Moderate (upper limbs elevation with jerks) 2 MCI 3.7b 13.6b 44.0 (FDS) Severe (lower limbs kicking) 3 PD 2.3b 12.1b 28.4 (BB) Mild (proximal four limbs jerking) 4 MCI 0b 10.6b 25.9 (BB) Mild (proximal four limbs jerking) 5 DLB 1.0b 14.4b 22.9 (BB) Mild (proximal four limbs jerking) 6 DLB 3.8b 10.9b 17.6b (BB) Mild (lower limbs jerking and repetitive hand movements) 7 MCI 1.4b 10.8b 15.0b (BB) Mild (sudden moderate trunk and four limbs jerking) 8 PD 2.8b 8.7b 13.5b (BB) Mild (proximal lower limbs jerking) 9 MCI 0b 8.2b 8.9b (BB) Severe (repetitive lower limbs kicking) BB = biceps brachii; DLB = dementia with Lewy bodies; FDS = flexor digitorum superficialis; MCI = mild cognitive impairment; MSA = multiple system atrophy; PD = Parkinson disease; RBD = REM sleep behavior disorder. Values are expressed as percentages. aNone of the nine patients had vocalizations during the recording. bRates below the proposed cut-offs for the diagnosis of IRBD (the proposed cut-offs for the diagnosis of IRBD are the following: ≥30% for tonic EMG activity in the mentalis, ≥15% for phasic EMG in the mentalis, ≥21.8% for “any” EMG activity in the mentalis plus bilateral biceps brachii, and ≥31.9 for “any” EMG activity in the mentalis plus bilateral flexor digitorum superficialis). Open in new tab Table 4 Electromyographic Activity Measures and Audiovisual Findings in the Nine Patients Who Had Electromyographic Activity in the Mentalis Below the Proposed Cut-Offs for the Diagnosis of RBD. Patient Emerging condition Tonic EMG activity in the mentalis (%) Phasic EMG activity in the mentalis (%) “Any” EMG activity in the mentalis plus phasic EMG activity in upper limbs (%) Severity and types of abnormal manifestations typical of RBD detected in the audiovisual recordings during REM sleepa 1 DLB 21.6b 8.6b 48.8 (BB) Moderate (upper limbs elevation with jerks) 2 MCI 3.7b 13.6b 44.0 (FDS) Severe (lower limbs kicking) 3 PD 2.3b 12.1b 28.4 (BB) Mild (proximal four limbs jerking) 4 MCI 0b 10.6b 25.9 (BB) Mild (proximal four limbs jerking) 5 DLB 1.0b 14.4b 22.9 (BB) Mild (proximal four limbs jerking) 6 DLB 3.8b 10.9b 17.6b (BB) Mild (lower limbs jerking and repetitive hand movements) 7 MCI 1.4b 10.8b 15.0b (BB) Mild (sudden moderate trunk and four limbs jerking) 8 PD 2.8b 8.7b 13.5b (BB) Mild (proximal lower limbs jerking) 9 MCI 0b 8.2b 8.9b (BB) Severe (repetitive lower limbs kicking) Patient Emerging condition Tonic EMG activity in the mentalis (%) Phasic EMG activity in the mentalis (%) “Any” EMG activity in the mentalis plus phasic EMG activity in upper limbs (%) Severity and types of abnormal manifestations typical of RBD detected in the audiovisual recordings during REM sleepa 1 DLB 21.6b 8.6b 48.8 (BB) Moderate (upper limbs elevation with jerks) 2 MCI 3.7b 13.6b 44.0 (FDS) Severe (lower limbs kicking) 3 PD 2.3b 12.1b 28.4 (BB) Mild (proximal four limbs jerking) 4 MCI 0b 10.6b 25.9 (BB) Mild (proximal four limbs jerking) 5 DLB 1.0b 14.4b 22.9 (BB) Mild (proximal four limbs jerking) 6 DLB 3.8b 10.9b 17.6b (BB) Mild (lower limbs jerking and repetitive hand movements) 7 MCI 1.4b 10.8b 15.0b (BB) Mild (sudden moderate trunk and four limbs jerking) 8 PD 2.8b 8.7b 13.5b (BB) Mild (proximal lower limbs jerking) 9 MCI 0b 8.2b 8.9b (BB) Severe (repetitive lower limbs kicking) BB = biceps brachii; DLB = dementia with Lewy bodies; FDS = flexor digitorum superficialis; MCI = mild cognitive impairment; MSA = multiple system atrophy; PD = Parkinson disease; RBD = REM sleep behavior disorder. Values are expressed as percentages. aNone of the nine patients had vocalizations during the recording. bRates below the proposed cut-offs for the diagnosis of IRBD (the proposed cut-offs for the diagnosis of IRBD are the following: ≥30% for tonic EMG activity in the mentalis, ≥15% for phasic EMG in the mentalis, ≥21.8% for “any” EMG activity in the mentalis plus bilateral biceps brachii, and ≥31.9 for “any” EMG activity in the mentalis plus bilateral flexor digitorum superficialis). Open in new tab Follow-up of these nine subjects showed that two eventually developed PD, three DLB and four MCI. The mean age at diagnostic V-PSG in this group of nine patients was 69.7 ± 4.7 years, the mean estimated RBD duration was 7.4 ± 6.9 years and the mean number of scored 3-second miniepochs was 953.1 ± 256.4. All nine individuals were men and four (44.4%) were referred to our sleep center because of other sleep complaints and not because of the dream-enacting behaviors (two because unexplained hypersomnolence and two for suspected obstructive sleep apnea). However, in these four patients specific questioning during the semistructured sleep interview at their first visit demonstrated a concomitant chronic history typical of RBD. In 36 (73.5%) patients the upper limb EMG activity was evaluated in the BB and in the remaining 13 (26.5%) in the FDS. All the 13 patients who underwent V-PSG using the EMG SINBAR montage (mentalis plus bilateral FDS) had EMG values above the cut-off for the diagnosis of IRBD (≥31.9%; Figure 2a). Four (11%) of the 36 patients who underwent baseline V-PSG using the EMG montage of the mentalis plus bilateral BB had EMG values below the cut-off for the diagnosis of IRBD (≥21.8%; Figure 2b). All four subjects did not reach either the tonic (≥30%) or the phasic (≥15%) cut-offs values using only the mentalis. In all of them the audiovisual recordings showed abnormal manifestation typical of RBD (Table 4). Follow-up of these four subjects showed that one eventually developed PD, one DLB and two MCI. Figure 2 Open in new tabDownload slide (2a) Percentages of “any” EMG activity in the mentalis plus phasic EMG activity in the bilateral flexor digitorum superficialis (FDS) of the 13 patients who eventually developed a clinically defined neurodegenerative syndrome using this EMG montage (horizontal bar indicates the previously published proposed cut-off of 31.9%) (2b) Percentages of “any” EMG activity in the mentalis plus phasic EMG activity in the bilateral biceps brachii (BB) of the 36 patients who eventually developed a clinically defined neurodegenerative syndrome using this EMG montage (horizontal bar indicates the previously published proposed cut-off of 21.8%).10 Figure 2 Open in new tabDownload slide (2a) Percentages of “any” EMG activity in the mentalis plus phasic EMG activity in the bilateral flexor digitorum superficialis (FDS) of the 13 patients who eventually developed a clinically defined neurodegenerative syndrome using this EMG montage (horizontal bar indicates the previously published proposed cut-off of 31.9%) (2b) Percentages of “any” EMG activity in the mentalis plus phasic EMG activity in the bilateral biceps brachii (BB) of the 36 patients who eventually developed a clinically defined neurodegenerative syndrome using this EMG montage (horizontal bar indicates the previously published proposed cut-off of 21.8%).10 Overall, for the diagnosis of IRBD, quantification of EMG activity in the mentalis plus upper limb muscles had a sensitivity of 91.8%, whereas the sensitivity for the isolated mentalis was of 81.6% (unilateral binomial test, p = .03). The rates of tonic EMG activity (Table 5) in the mentalis muscle in the 15 patients who developed PD were significantly higher than those of the 32 patients that developed DLB or MCI or in the 19 who developed DLB. There were no significant differences in the measurement of phasic EMG activity in the mentalis and in the measurement of combined “any” EMG activity in the mentalis with bilateral phasic BB between patients who developed PD and those who developed DLB or MCI or in the patients who developed DLB. There were not sufficient patients on the groups of each neurodegenerative syndrome to compare the measurement of combined “any” EMG activity in the mentalis with bilateral phasic FDS. Table 5 EMG Activity in Each Type of Emerging Disease. PD (n = 15) DLB (n = 19) MCI (n = 13) p (PD vs. DLB) p (PD vs. DLB + MCI) Tonic EMG activity in mentalis (%) 48.2 ± 36.5a 24.6 ± 25.4 27.2 ± 38.1 .036 .034 Phasic EMG activity in mentalis (%) 35.4 ± 19.4 26.5 ± 10.9 26.4 ± 16.0 .103 .069 Combined “any” EMG activity in mentalis with bilateral phasic BB (%) (n = 36)a 63.8 ± 31.4 (n = 11) 54.9 ± 20.2 (n = 16) 42.3 ± 34.0 (n = 7) .377 .238 PD (n = 15) DLB (n = 19) MCI (n = 13) p (PD vs. DLB) p (PD vs. DLB + MCI) Tonic EMG activity in mentalis (%) 48.2 ± 36.5a 24.6 ± 25.4 27.2 ± 38.1 .036 .034 Phasic EMG activity in mentalis (%) 35.4 ± 19.4 26.5 ± 10.9 26.4 ± 16.0 .103 .069 Combined “any” EMG activity in mentalis with bilateral phasic BB (%) (n = 36)a 63.8 ± 31.4 (n = 11) 54.9 ± 20.2 (n = 16) 42.3 ± 34.0 (n = 7) .377 .238 BB = biceps brachii; PD = Parkinson disease; DLB = dementia with Lewy bodies; MCI = mild cognitive impairment; EMG = electromyography. Values are expressed as mean ± standard deviation. aTwo patients were diagnosed with multiple system atrophy and are not shown in the table. Open in new tab Table 5 EMG Activity in Each Type of Emerging Disease. PD (n = 15) DLB (n = 19) MCI (n = 13) p (PD vs. DLB) p (PD vs. DLB + MCI) Tonic EMG activity in mentalis (%) 48.2 ± 36.5a 24.6 ± 25.4 27.2 ± 38.1 .036 .034 Phasic EMG activity in mentalis (%) 35.4 ± 19.4 26.5 ± 10.9 26.4 ± 16.0 .103 .069 Combined “any” EMG activity in mentalis with bilateral phasic BB (%) (n = 36)a 63.8 ± 31.4 (n = 11) 54.9 ± 20.2 (n = 16) 42.3 ± 34.0 (n = 7) .377 .238 PD (n = 15) DLB (n = 19) MCI (n = 13) p (PD vs. DLB) p (PD vs. DLB + MCI) Tonic EMG activity in mentalis (%) 48.2 ± 36.5a 24.6 ± 25.4 27.2 ± 38.1 .036 .034 Phasic EMG activity in mentalis (%) 35.4 ± 19.4 26.5 ± 10.9 26.4 ± 16.0 .103 .069 Combined “any” EMG activity in mentalis with bilateral phasic BB (%) (n = 36)a 63.8 ± 31.4 (n = 11) 54.9 ± 20.2 (n = 16) 42.3 ± 34.0 (n = 7) .377 .238 BB = biceps brachii; PD = Parkinson disease; DLB = dementia with Lewy bodies; MCI = mild cognitive impairment; EMG = electromyography. Values are expressed as mean ± standard deviation. aTwo patients were diagnosed with multiple system atrophy and are not shown in the table. Open in new tab DISCUSSION We have shown in this study including patients with IRBD who later develop a clinically defined neurodegenerative syndrome that the EMG recording of the upper limbs in addition to the mentalis muscle is important for the correct identification of IRBD. If we had only used the mentalis we would have missed 18.4% of true IRBD patients. Our results support the concept that recording upper limb muscles increases the ability to identify IRBD by V-PSG. This may be in part due to the fact that the mentalis do not detect epochs when the patient displays abnormal behaviors involving only the limbs and not the head, which is a common situation in RBD.11 A previous study showed that isolated recording of the mentalis does not capture 35.5% of the behavioral events seen or heard on video while simultaneous recording of mentalis, right and left FDS only misses 4.6% of 3-second miniepochs containing motor events or vocalizations.19 The EMG quantification of combined upper limbs and mentalis muscles, as proposed by the SINBAR group,10,11 would have missed four (8.2%) IRBD patients. These four patients would have not been qualified as having “excessive” EMG activity during REM sleep in any of the two EMG montages. In these four cases visualization of abnormal behaviors typical of RBD with synchronized audiovisual recording was determinant for making the diagnosis of IRBD. This finding indicates that identification in REM sleep of behavioral abnormalities typical of RBD by audiovisual analysis in V-PSG is essential for the diagnosis of IRBD. Abnormally increased EMG activity in the mentalis (both phasic and tonic) is considered an essential requirement in the diagnosis of RBD.2 In our study, however, there were patients who later developed a defined neurodegenerative syndrome that clearly had very low levels of mentalis EMG activity and even in five cases tonic EMG activity was absent in any of the REM epochs analyzed. Several factors can account for this observation. First, we cannot exclude that the rates of muscular activity in these subjects could be higher if a second V-PSG night would have been recorded (intra-individual night to night variability). Second, methodological aspects in the quantification of EMG activity may also be responsible of these variabilities (eg, using two or four times the background amplitude; using 2 or 3-second miniepochs for quantifying phasic activity; using 20 vs. 30-second epochs9,10; having an absolute amplitude criteria; or differences in defining the background for the tonic activity).9–11,20,21 Finally, it is also possible that there are true IRBD patients with a different profiles showing low amounts of EMG activity in the mentalis during REM sleep. In fact, seven of the nine patients who had EMG activity below the cut-offs for the mentalis were later diagnosed with cognitive impairment (MCI or DLB). We have found in this study that IRBD patients who developed PD had higher amounts of tonic EMG activity in the mentalis than those who developed DLB or MCI. In line with this finding, another study20 reported that IRBD patients converting to PD had higher rates of tonic EMG activity in the mentalis than patients remaining disease-free. Strengths of our study are the inclusion of a homogeneous group of subjects with IRBD who later developed a defined neurodegenerative syndrome, the fact that the scorer was blind to the condition of the subjects, that we included a detailed analysis of the audiovisual recordings, and that we excluded individuals who were treated with medications capable to modify the quantity of muscular activity during REM sleep. A possible limitation of this study was the inclusion of patients with mild to moderate sleep apnea. It is unknown if an elevated index of respiratory events interferes with the analysis of EMG activity after arousals and respiratory-related EMG increases in the mentalis were carefully excluded from the measurements.9,22 Although the presence of apneic events during REM sleep might decrease the number of 30-second epochs and 3-second miniepochs available for analysis, we did not find, however, differences in the duration of the REM sleep between patients with apneic events and those without them. Also, we cannot fully exclude that the evaluation of the FDS instead of the BB could have produced higher rates of EMG activity and reduce the number of false negatives, since all 13 patients evaluated with the FDS had values above the cut-offs. In summary, this is the first study comparing two different manual EMG methods for the diagnosis of IRBD analyzing patients who eventually developed a clinical defined neurodegenerative syndrome. 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Diagnostic thresholds for quantitative REM sleep phasic burst duration, phasic and tonic muscle activity, and REM atonia index in REM sleep behavior disorder with and without comorbid obstructive sleep apnea . Sleep . 2014 ; 37 ( 10 ): 1649 – 1662 . Google Scholar Crossref Search ADS PubMed WorldCat Author notes Address correspondence to: Joan Santamaria, Neurology Service, Hospital Clinic de Barcelona, C/ Villarroel 170, Barcelona 08036, Spain. Telephone: 3493-227-5413; Fax: 3493-227-5783; Email: [email protected] © Sleep Research Society 2017. Published by Oxford University Press on behalf of the Sleep Research Society. All rights reserved. For permissions, please e-mail [email protected].

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Published: Apr 1, 2017

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