The clinical significance of 10-m walk test standardizations in Parkinson’s disease

The clinical significance of 10-m walk test standardizations in Parkinson’s disease Background The 10-m walk test (10MWT) is a widely used measure of gait speed in Parkinson’s disease (PD). However, it is unclear if different standardizations of its conduct impact test results. Aim of the study We examined the clinical significance of two aspects of the standardization of the 10MWT in mild PD: static vs. dynamic start, and a single vs. repeated trials. Implications for fall prediction were also explored. Methods 151 people with PD (mean age and PD duration, 68 and 4 years, respectively) completed the 10MWT in comfort- able gait speed with static and dynamic start (two trials each), and gait speed (m/s) was recorded. Participants then registered all prospective falls for 6 months. Results Absolute mean differences between outcomes from the various test conditions ranged between 0.016 and 0.040 m/s (effect sizes, 0.06–0.14) with high levels of agreement (intra-class correlation coefficients, 0.932–0.987) and small standard errors of measurement (0.032–0.076 m/s). Receiver operating characteristic curves showed similar discriminate abilities for prediction of future falls across conditions (areas under curves, 0.70–0.73). Cut-off points were estimated at 1.1–1.2 m/s. Conclusions Different 10MWT standardizations yield very similar results, suggesting that there is no practical need for an acceleration distance or repeated trials when conducting this test in mild PD. Keywords Parkinson disease · The 10-m walk test · Test standardization · Falls · Prediction Introduction suggested as an important predictor of future falls in PD [2–5]. However, there are different standardizations for the The 10-m walk test (10MWT) is widely used and recom- conduct of the 10MWT, for example, measuring over differ - mended as a measure of gait speed in Parkinson’s disease ent distances (10 or 6 m) and the inclusion or exclusion of an (PD). Its measurement properties are considered good acceleration distance, i.e., dynamic vs. static start [1–3, 6]. and the test can be used to identify changes in gait speed According to general principles of measurement uncer- in response to therapeutic interventions [1]. Furthermore, tainty, the best estimate of any measured quantity is the comfortable gait speed < 1.1 m per second (m/s) has been mean of repeated measures obtained under identical condi- tions [7]. Therefore, it is common to perform multiple tri- als and use the mean of these as the test result [8, 9]. For example, the 3-step falls prediction model (3-step model) * Beata Lindholm Beata.Lindholm@med.lu.se prescribes the use of the mean value of two trials [2, 3]. However, it is unclear to what extent different 10MWT Department of Neurology and Rehabilitation Medicine, standardizations impact test outcomes and interpretations. Skåne University Hospital, 205 02 Malmö, Sweden In this respect, the clinical significance of any differences in Clinical Memory Research Unit, Department of Clinical outcome is not primarily related to the statistical significance Sciences, Lund University, Malmö, Sweden resulting from null hypothesis testing and similar procedures Department of Health Sciences, Lund University, Lund, (where, e.g., sample size is a major determinant). Instead, Sweden aspects such as effect sizes, absolute differences relative Memory Clinic, Skåne University Hospital, Malmö, Sweden to estimated errors of measurement, and decision-making The PRO-CARE Group, School of Health and Society, implications are more relevant to consider [10]. Therefore, Kristianstad University, Kristianstad, Sweden Vol.:(0123456789) 1 3 1830 Journal of Neurology (2018) 265:1829–1835 we examined the clinical significance of two aspects of the Detailed descriptions regarding the overall procedures standardization of conducting the 10MWT in mild PD: (1) are available elsewhere [11]. Participants were assessed using static vs. dynamic start and (2) using data from a sin- during an outpatient visit, scheduled at a time of day when gle vs. two repeated trials. In addition, the implications of they reported to typically feel at best. The 10MWT was con- these standardizations in terms of prediction of future falls ducted in comfortable gait speed following a verbal start were explored. command. Timing according to static start (ss) was done over the first 10 m, and timing according to dynamic start (ds) was done between 2 and 12 m. Walking aids were per- mitted. Walking time was measured to the nearest 0.001 s Methods (s) using a digital stopwatch (Origo, model 365,510) when the lead foot crossed the respective markers (at 0, 2, 10 and Participants were enrolled in a cohort study designed to 12 m), and rounded to the closest 0.01 s. Two trials (t1 and study factors associated with falls and near falls in PD t2) each of ss and ds were conducted. Gait speed was cal- [11]. All people diagnosed with PD that received care at culated as m/s. a south Swedish university hospital neurology outpatient In addition, participants were assessed regarding various clinic during 2007–2013 were considered eligible for inclu- aspects of their PD, including disease severity (Hoehn and sion (n = 359). Exclusion criteria were age above 80 years Yahr staging (HY)) [12], motor symptoms (part III of the (n = 121), inability to understand instructions (n = 14), ina- Unified PD Rating Scale (UPDRS)) [13], and cognition (the bility to stand without support (n = 22) and severe comorbid- mini-mental state examination (MMSE)) [14]. Freezing of ity (n = 11). Of the remaining 191 potential participants, 40 gait (FOG) was investigated with item 3 of the self-adminis- declined participation, leaving 151 participants (68 women) tered Freezing of Gait Questionnaire (FOGQsa) (Do you feel in the final study sample (Table  1). The Regional Ethical that your feet get glued to the floor while walking, making a Review Board approved the study (Dnr 2011/768). All par- turn or when trying to initiate walking (freezing)?). Those ticipants gave written informed consent. scoring ≥ 1 were categorized as having FOG [15, 16]. Table 1 Sample characteristics Age (years), mean (SD; min–max) 68 (9.6; 35–80) (n = 151) Female gender, n (%) 68 (45) PD duration (years), mean (SD; min–max) 4 (4; 0.1–17) Stage of disease (HY), median (q1–q3; min–max) II (II–III; I–IV)  HY I, n (%) 12 (8)  HY II, n (%) 87 (57.5)  HY III, n (%) 45 (30)  HY IV, n (%) 7 (4.5) Motor symptoms (UPDRS III), median (q1–q3; min–max) 12 (8–18; 1–46) Cognition (MMSE), median (q1–q3; min–max) 28 (26–29; 18–30) d, n = 150 History of FOG, n (%) 63 (42) Walking aids, n (%) 19 (13)  Cane 3 (2)  Crutch 3 (2)  Walker 13 (9) e, n=146 Individuals with one or more prospective falls, n (%) 47 (32) PD Parkinson’s disease, q1–q3 1st–3rd quartile, HY Hoehn and Yahr stage of PD, UPDRS III part III (motor examination) of the Unified Parkinson’s Disease Rating Scale, MMSE mini-mental state examina- tion, FOG freezing of gait Stages range between I (mild unilateral disease) and V (confined to bed or wheelchair unless aided) Scores range 0–108 (0 = better) Scores range 0–30 (30 = better) People scoring ≥ 1 on the self-administered Freezing of Gait Questionnaire (FOGQsa), item 3 (Do you feel that your feet get glued to the floor while walking, making a turn or when trying to initiate walking (freez- ing)?) were categorized as having FOG As determined using a prospective falls diary during a 6-month follow-up (see Lindholm et  al. [11] for details) 1 3 Journal of Neurology (2018) 265:1829–1835 1831 As the last step during the outpatient visit, participants Results were instructed to register all consecutive falls and near falls during the following 6 months [17]. They were pro- All 151 participants completed the 10MWT testing. Sam- vided with a diary folder consisting of pre-printed pages ple characteristics are summarized in Table  1. Partici- for recording the date and time of every event and questions pants’ mean (SD) age and PD duration were 68 (9.6) and clarifying whether the incident was a fall. The question was 4 (4) years, respectively; their median (q1–q3) Hoehn and phrased as follows: Did you fall in such a way that your Yahr (HY) stages were II (II–III). Freezing of gait (FOG) body hit the ground? Falls were defined as “an unexpected was experienced by 63 (42%) participants, and 21 (14%) event in which the participants come to rest on the ground, were in HY stage IV or used walking aids during test- floor, or lower level” [17]. The definition of a fall was thor - ing. At the time of assessments, 143 participants (95%) oughly described during the outpatient visit. All participants rated their motor status as “on” or “on with dyskinesias” were telephoned monthly to ensure that registrations had and 8 (5%) rated it as “off”. One hundred forty-six (97%) been completed according to instructions. During the last individuals completed prospective follow-up during the telephone call, they were requested to return the diary folder 6-month period. Forty-seven of those (32%) reported at in a pre-stamped envelope. least one fall and 28 (19%) reported more than one fall. There were statistically significant differences (P < 0.001) in gait speed at all instances in the full group (n = 151). Analyses Absolute mean differences between outcomes from the vari- ous test conditions were generally small, ranging between Data were analysed using IBM SPSS version 22 (IBM Corp., 0.016 and 0.040 m/s (ESs 0.06–0.14) with high levels of Armonk, NY) with the alpha level of significance set at 0.05 agreement (ICC 0.932–0.987) and small measurement errors ( two tailed). Paired sample t tests were used to explore dif- (SEM 0.032–0.076  m/s). Further details are provided in ferences between different standardizations of the 10MWT Table 2. Similar results were also obtained when repeating (ss vs. ds) conducted at t1 and t2, as well as the mean values these analyses among subgroups of individuals with a his- of these (M vs. M ). Similarly, we examined the differ - tory of FOG (n = 63; Table 3) and those in HY stage IV or ss ds ences between trials (t1 vs. t2), and between t1 and mean t1 using walking aids during testing (n = 21; Table 4), as well and t2 values (M ) for ss and ds, respectively. Effect sizes as among those who self-rated their motor status as “off” t1, t2 (ESs) were computed using Cohen’s d; ESs were interpreted during testing (n = 8; data not shown). as small (0.20), moderate (0.50), large (0.80) and very large Forty-seven of 151 participants (32%) reported at least (1.3) [10]. Intra-class correlation (ICC) coefficients (two- one prospective fall during the 6-month follow-up. ROC way mixed effects model, absolute agreement, single meas- curve analyses showed similar discriminate abilities for ure) were calculated to determine the agreement between future falls across the various 10MWT test conditions test conditions, and the standard error of measurement (AUROC, 0.70–0.73). The Youden index ranged between (SEM) was estimated (SD × √[1-ICC]). The analyses were 0.37 and 0.39, with corresponding cut-off points estimated t1 performed for the full sample (n = 151). In addition, explora- at 1.1–1.2 m/s (Table 5). tory subgroup analyses were conducted among (1) people with a history of FOG (n = 63), (2) those in HY stage IV and/ or using walking aids during testing (n = 21), (3) those who self-rated their motor status as “off” during testing (n = 8). Discussion Receiver operating characteristic (ROC) curve analysis was used to determinate optimal gait speed cut-off points We examined the effects of different standardizations of the for prediction of one or more future falls in the full group 10MWT in people with relatively mild PD. Although com- (n = 151). The optimal point is that with the highest true- parisons showed statistically significant differences between positive (sensitivity) and lowest false-positive (1-specific- testing conditions, the sizes of these differences were small ity) values. The areas under the ROC curves (AUROCs) can and the various test results showed high levels of agree- range between 0 and 1, where an AUROC <0.5 indicates ment. The measurement error (SEM) has been suggested that a test performs worse than chance; AUROCs ≥ 0.7 are as a distribution-based minimal important difference (MID) acceptable, with values between 0.7 and 0.9 and >0.9 con- indicator, at and above which differences in outcomes reflect sidered moderate and high, respectively [18, 19]. Values differences of clinical interest [20]. In this study, the SEM (m/s) associated with the highest Youden index (sensitiv- values exceeded absolute mean differences by factors of ity + specificity − 1) were estimated as the optimal cut-off 1.9–2.4. When considering the three subgroups, SEM values points to discriminate between those with and without future exceeded absolute mean differences by factors of up to 23. falls [19]. 1 3 1832 Journal of Neurology (2018) 265:1829–1835 Table 2 Gait speed characteristics according to different standardizations of the 10-m walk test in PD (n = 151) a,b c d a Mean (SD) Mean difference (95% CI) ES ICC (95% CI) SEM Static vs. dynamic start  t1 vs. t1 (n = 150) 1.111 (0.292) vs. 1.094 (0.277) 0.017 (0.08, 0.0259) 0.06 0.980 (0.971, 0.987) 0.041 ss ds  t2 vs. t2 (n = 149) 1.153 (0.298) vs. 1.129 (0.286) 0.024 (0.011, 0.357) 0.08 0.964 (0.946, 0.975) 0.057 ss ds  M vs. M n = 149) 1.132 (0.290) vs. 1.112 (0.278) 0.020 (0.012, 0.028) 0.07 0.983 (0.970, 0.989) 0.037 ss ds ( Static start (n = 150)  t1 vs. t2 1.114 (0.291) vs. 1.154 (0.297) − 0.040 (− 0.057, − 0.024) 0.14 0.932 (0.890, 0.956) 0.076 ss ss  t1 vs. M 1.114 (0.291) vs. 1.134 (0.290) − 0.020 (− 0.028, − 0.012) 0.07 0.982 (0.971, 0.989) 0.039 ss t1,t2 Dynamic start (n = 149)  t1 vs. t2 1.096 (0.277) vs. 1.129 (0.286) − 0.033 (− 0.047, − 0.020) 0.12 0.950 (0.917, 0.968) 0.062 ds ds  t1 vs. M 1.096 (0.277) vs. 1.112 (0.278) − 0.016 (− 0.024, − 0.010) 0.06 0.987 (0.978, 0.992) 0.032 ds t1,t2 PD Parkinson’s disease, m/s meters per second, SD standard deviation, CI confidence interval, ES effect size, ICC intra-class correlation, SEM standard error of measurement (SD × √1– ICC), t1 trial 1 with static start, t1 trial 1 with dynamic start, t2 trial 2 with static start, t2 trial t1 ss ds ss ds 2 with dynamic start, M mean value of trials 1 and 2 with static start, M mean value of trials 1 and 2 with dynamic start, M mean value of ss ds t1,t2 trials 1 and 2 Data are in m/s P < 0.001 in all instances (paired samples t tests) Cohen’ s d (calculated on between-test differences) Two-way mixed effects model (absolute agreement, single measure) Table 3 Gait speed characteristics according to different standardizations of the 10-m walk test in individuals with PD and history of FOG (n = 63) a,b c d a Mean (SD) Mean difference (95% CI) ES ICC (95% CI) SEM Static vs. dynamic start  t1 vs. t1 n = 63) 0.943 (0.284) vs. 0.934 (0.272) 0.009 (− 0.008, 0.022) 0.03 0.977 (0.963, 0.986) 0.043 ss ds (  t2 vs. t2 (n = 62) 0.990 (0.308) vs. 0.971 (0.298) 0.019 (− 0.004, 0.044) 0.06 0.950 (0.918, 0.970) 0.068 ss ds  M vs. M (n = 62) 0.968 (0.293) vs. 0.954 (0.282) 0.014 (− 0.002, 0.029) 0.05 0.977 (0.962, 0.986) 0.044 ss ds Static start (n = 62)  t1 vs. t2 0.945 (0.287) vs. 0.990 (0.308) − 0.045 (− 0.076, − 0.021) 0.15 0.934 (0.867, 0.964) 0.073 ss ss  t1 vs. M 0.945 (0.287) vs. 0.968 (0.293) − 0.023 (− 0.036, − 0.011) 0.08 0.982 (0.963, 0.991) 0.039 ss t1,t2 Dynamic start (n = 62)  t1 vs. t2 0.937 (0.274) vs. 0.971 (0.298) − 0.034 (− 0.058, − 0.008) 0.12 0.937 (0.891, 0.963) 0.068 ds ds  t1 vs. M 0.937 (0.274) vs. 0.954 (0.282) − 0.017 (− 0.029, − 0.004) 0.06 0.983 (0.970, 0.985) 0.036 ds t1,t2 PD Parkinson’s disease, FOG freezing of gait, m/s meters per second, SD standard deviation, CI confidence interval, ES effect size, ICC intra- class correlation, SEM standard error of measurement (SD × √1– ICC), t1 , trial 1 with static start, t1 trial 1 with dynamic start, t2 trial 2 t1 ss ds ss with static start, t2 , trial 2 with dynamic start, M mean value of trials 1 and 2 with static start, M mean value of trials 1 and 2 with dynamic ds ss ds start, M mean value of trials 1 and 2 t1,t2 Data are in m/s P < 0.01 in all instances (paired samples t tests) in all instances but comparisons between static vs. dynamic start (P ≥ 0.082) Cohen’ s d (calculated on between-test differences) Two-way mixed effects model (absolute agreement, single measure) It has been suggested that FOG may affect the outcome Taken together, these observations provide evidence that of the 10MWT [1]. Indeed, individuals with FOG walked observed differences across test conditions can be consid- slower when compared to the whole group. Although we ered clinically trivial. Previous anchor-based MID estimates did not observe any FOG during testing, 10MWT-based gait in non-PD samples have ranged from 0.10 to 0.16 m/s [1]. speed estimates were in agreement across standardizations Taking these estimates into account, the clinical meaning- also among people who reported having FOG. This may fulness of the observed differences diminishes even further. have been due to the use of a start command or straight In accordance with assumptions regarding the mean of walkway during 10MWT. repeated measures obtained under identical conditions as 1 3 Journal of Neurology (2018) 265:1829–1835 1833 Table 4 Gait speed characteristics according to different standardizations of the 10-m walk test in individuals with PD in HY stage IV or using walking aids during testing (n = 21) a,b c d a Mean (SD) Mean difference (95% CI) ES ICC (95% CI) SEM Static vs. dynamic start  t1 vs. t1 (n = 21) 0.700 (0.189) vs. 0.698 (0.154) 0.002 (− 0.029, 0.036) 0.01 0.941 (0.853, 0.977) 0.046 ss ds  t2 vs. t2 (n = 20) 0.722 (0.205) vs. 0.701 (0.160) 0.021 (− 0.015, 0.057) 0.11 0.920 (0.802, 0.969) 0.058 ss ds  M vs. M (n = 20) 0.694 (0.154) vs. 0.706 (0.196) − 0.012 (− 0.021, 0.045) 0.07 0.931(0.829, 0.974) 0.040 ss ds Static start (n = 20)  t1 vs. t2 0.690 (0.189) vs. 0.722 (0.205) − 0.032 (− 0.061, − 0.003) 0.16 0.947 (0.838, 0.981) 0.044 ss ss  t1 vs. M 0.690 (0.190) vs. 0.706 (0.196) − 0.016 (− 0.030, − 0.002) 0.08 0.986 (0.954, 0.995) 0.022 ss t1,t2 Dynamic start (n = 20)  t1 vs. t2 0.688 (0.152) vs. 0.701 (0.160) − 0.013 (− 0.040, 0.013) 0.08 0.943 (0.857, 0.978) 0.036 ds ds  t1 vs. M 0.688 (0.152) vs. 0.695 (0.154) − 0.007 (− 0.020, 0.006) 0.05 0.985 (0.962, 0.994) 0.019 ds t1,t2 PD Parkinson’s disease, HY Hoehn and Yahr stage of PD, m/s meters per second, SD standard deviation, CI confidence interval, ES effect size, ICC intra-class correlation, SEM standard error of measurement (SD × √1– ICC), t1 trial 1 with static start, t1 trial 1 with dynamic start, t1 ss ds t2 trial 2 with static start, t2 trial 2 with dynamic start, M mean value of trials 1 and 2 with static start, M mean value of trials 1 and 2 with ss ds ss ds dynamic start, M mean value of trials 1 and 2 t1,t2 Data are in m/s P ≥ 0.298 in all instances (paired samples t tests) but t2 vs. t2 (static vs. dynamic start; P = 0.031), t1 vs. t2 and t1 vs. M (static start; ss ds ss ss ss t1,t2 P = 0.031) Cohen’ s d (calculated on between-test differences) Two-way mixed effects model (absolute agreement, single measure) Table 5 Discriminant ability of b c d e AUROC (95% CI) Cut-off Sensitivity SpecificityYouden index the 10-m walk test (10MWT) point (m/s) for identification of individuals with prospective falls (n = 146) Static start  t1 0.72 (0.64, 0.81) 1.1 0.70 0.69 0.39  t2 0.72 (0.63, 0.81) 1.2 0.70 0.69 0.39  M 0.73 (0.64, 0.81) 1.1 0.67 0.70 0.37 t1,t2 Dynamic start  t1 0.71 (0.62, 0.80) 1.1 0.72 0.66 0.38  t2 0.70 (0.60, 0.79) 1.1 0.70 0.67 0.37  M 0.70 (0.61, 0.80) 1.1 0.70 0.68 0.38 t1,t2 m/s meters per second, t1 trial 1, t2 trial 2, M mean value of t1 and t2 t1,t2 As determined using a prospective fall diary during a 6-month follow-up (see Lindholm et  al. 2015 for details) Area under the receiver operating characteristic curves of t1, t2 and M during 10MWT with static and t1,t2 dynamic start The proportion of people with prospective falls who had a positive result (scored above the cut-off point) The proportion of people without prospective falls who had a negative result (scored below the cut-off point) Sensitivity + specificity− 1 the best estimate of any measured quantity [7], mean val- practical situations. Similarly, the negligible differences ues from trials 1 and 2 yielded smaller differences, effect between static and dynamic start suggest that the accelera- sizes and SEM values together with larger ICCs than sin- tion distance does not appear to affect the estimated gait gle-observation data from trials 1 and 2. However, given speed considerably. The finding that repeated trials and that the observed differences were very small, it is ques- dynamic start do not appear to have any practical impact tionable if they are of any clinical significance. Therefore, on 10MWT-based outcomes simplifies its conduct and unless there is a specific reason to maximise precision, our should facilitate its use in routine clinical practice. findings suggest that a single trial is sufficient for most 1 3 1834 Journal of Neurology (2018) 265:1829–1835 The observations discussed above were also corrobo- Compliance with ethical standards rated when exploring the implications of different 10MWT Conflicts of interest All authors declare that they have no conflict of standardizations in terms of predicting future falls. The interest. discriminant abilities of both static and dynamic start were very similar for both single trials and mean values. It is also Ethical standard The study was approved by the institutional review noteworthy that trial 1 values and mean (trials 1 and 2) val- board and was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. ues of both static and dynamic start identified 1.1 m/s as an optimal cut-off point. This finding is in line with the sug- gested cut-off point for comfortable gait speed as a predictor Open Access This article is distributed under the terms of the Crea- tive Commons Attribution 4.0 International License (http://creat iveco in the 3-step model [2, 3]. However, while the 3-step model mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- prescribes the use of the mean of two trials, our observations tion, and reproduction in any medium, provided you give appropriate suggest that a single trial with static start will suffice. credit to the original author(s) and the source, provide a link to the Although this study strengthens the current evidence base Creative Commons license, and indicate if changes were made. regarding the conduct of the 10MWT in PD, it has some limitations that should be acknowledged. The study involved people with relatively mild PD, and people above the age of 80 years were not included. Our findings may, therefore, References not be applicable to older people with mild PD and those 1. Bloem BR, Marinus J, Almeida Q, Dibble L, Nieuwboer A, Post in more advanced PD stages. 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The clinical significance of 10-m walk test standardizations in Parkinson’s disease

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Medicine & Public Health; Neurology; Neurosciences; Neuroradiology
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Abstract

Background The 10-m walk test (10MWT) is a widely used measure of gait speed in Parkinson’s disease (PD). However, it is unclear if different standardizations of its conduct impact test results. Aim of the study We examined the clinical significance of two aspects of the standardization of the 10MWT in mild PD: static vs. dynamic start, and a single vs. repeated trials. Implications for fall prediction were also explored. Methods 151 people with PD (mean age and PD duration, 68 and 4 years, respectively) completed the 10MWT in comfort- able gait speed with static and dynamic start (two trials each), and gait speed (m/s) was recorded. Participants then registered all prospective falls for 6 months. Results Absolute mean differences between outcomes from the various test conditions ranged between 0.016 and 0.040 m/s (effect sizes, 0.06–0.14) with high levels of agreement (intra-class correlation coefficients, 0.932–0.987) and small standard errors of measurement (0.032–0.076 m/s). Receiver operating characteristic curves showed similar discriminate abilities for prediction of future falls across conditions (areas under curves, 0.70–0.73). Cut-off points were estimated at 1.1–1.2 m/s. Conclusions Different 10MWT standardizations yield very similar results, suggesting that there is no practical need for an acceleration distance or repeated trials when conducting this test in mild PD. Keywords Parkinson disease · The 10-m walk test · Test standardization · Falls · Prediction Introduction suggested as an important predictor of future falls in PD [2–5]. However, there are different standardizations for the The 10-m walk test (10MWT) is widely used and recom- conduct of the 10MWT, for example, measuring over differ - mended as a measure of gait speed in Parkinson’s disease ent distances (10 or 6 m) and the inclusion or exclusion of an (PD). Its measurement properties are considered good acceleration distance, i.e., dynamic vs. static start [1–3, 6]. and the test can be used to identify changes in gait speed According to general principles of measurement uncer- in response to therapeutic interventions [1]. Furthermore, tainty, the best estimate of any measured quantity is the comfortable gait speed < 1.1 m per second (m/s) has been mean of repeated measures obtained under identical condi- tions [7]. Therefore, it is common to perform multiple tri- als and use the mean of these as the test result [8, 9]. For example, the 3-step falls prediction model (3-step model) * Beata Lindholm Beata.Lindholm@med.lu.se prescribes the use of the mean value of two trials [2, 3]. However, it is unclear to what extent different 10MWT Department of Neurology and Rehabilitation Medicine, standardizations impact test outcomes and interpretations. Skåne University Hospital, 205 02 Malmö, Sweden In this respect, the clinical significance of any differences in Clinical Memory Research Unit, Department of Clinical outcome is not primarily related to the statistical significance Sciences, Lund University, Malmö, Sweden resulting from null hypothesis testing and similar procedures Department of Health Sciences, Lund University, Lund, (where, e.g., sample size is a major determinant). Instead, Sweden aspects such as effect sizes, absolute differences relative Memory Clinic, Skåne University Hospital, Malmö, Sweden to estimated errors of measurement, and decision-making The PRO-CARE Group, School of Health and Society, implications are more relevant to consider [10]. Therefore, Kristianstad University, Kristianstad, Sweden Vol.:(0123456789) 1 3 1830 Journal of Neurology (2018) 265:1829–1835 we examined the clinical significance of two aspects of the Detailed descriptions regarding the overall procedures standardization of conducting the 10MWT in mild PD: (1) are available elsewhere [11]. Participants were assessed using static vs. dynamic start and (2) using data from a sin- during an outpatient visit, scheduled at a time of day when gle vs. two repeated trials. In addition, the implications of they reported to typically feel at best. The 10MWT was con- these standardizations in terms of prediction of future falls ducted in comfortable gait speed following a verbal start were explored. command. Timing according to static start (ss) was done over the first 10 m, and timing according to dynamic start (ds) was done between 2 and 12 m. Walking aids were per- mitted. Walking time was measured to the nearest 0.001 s Methods (s) using a digital stopwatch (Origo, model 365,510) when the lead foot crossed the respective markers (at 0, 2, 10 and Participants were enrolled in a cohort study designed to 12 m), and rounded to the closest 0.01 s. Two trials (t1 and study factors associated with falls and near falls in PD t2) each of ss and ds were conducted. Gait speed was cal- [11]. All people diagnosed with PD that received care at culated as m/s. a south Swedish university hospital neurology outpatient In addition, participants were assessed regarding various clinic during 2007–2013 were considered eligible for inclu- aspects of their PD, including disease severity (Hoehn and sion (n = 359). Exclusion criteria were age above 80 years Yahr staging (HY)) [12], motor symptoms (part III of the (n = 121), inability to understand instructions (n = 14), ina- Unified PD Rating Scale (UPDRS)) [13], and cognition (the bility to stand without support (n = 22) and severe comorbid- mini-mental state examination (MMSE)) [14]. Freezing of ity (n = 11). Of the remaining 191 potential participants, 40 gait (FOG) was investigated with item 3 of the self-adminis- declined participation, leaving 151 participants (68 women) tered Freezing of Gait Questionnaire (FOGQsa) (Do you feel in the final study sample (Table  1). The Regional Ethical that your feet get glued to the floor while walking, making a Review Board approved the study (Dnr 2011/768). All par- turn or when trying to initiate walking (freezing)?). Those ticipants gave written informed consent. scoring ≥ 1 were categorized as having FOG [15, 16]. Table 1 Sample characteristics Age (years), mean (SD; min–max) 68 (9.6; 35–80) (n = 151) Female gender, n (%) 68 (45) PD duration (years), mean (SD; min–max) 4 (4; 0.1–17) Stage of disease (HY), median (q1–q3; min–max) II (II–III; I–IV)  HY I, n (%) 12 (8)  HY II, n (%) 87 (57.5)  HY III, n (%) 45 (30)  HY IV, n (%) 7 (4.5) Motor symptoms (UPDRS III), median (q1–q3; min–max) 12 (8–18; 1–46) Cognition (MMSE), median (q1–q3; min–max) 28 (26–29; 18–30) d, n = 150 History of FOG, n (%) 63 (42) Walking aids, n (%) 19 (13)  Cane 3 (2)  Crutch 3 (2)  Walker 13 (9) e, n=146 Individuals with one or more prospective falls, n (%) 47 (32) PD Parkinson’s disease, q1–q3 1st–3rd quartile, HY Hoehn and Yahr stage of PD, UPDRS III part III (motor examination) of the Unified Parkinson’s Disease Rating Scale, MMSE mini-mental state examina- tion, FOG freezing of gait Stages range between I (mild unilateral disease) and V (confined to bed or wheelchair unless aided) Scores range 0–108 (0 = better) Scores range 0–30 (30 = better) People scoring ≥ 1 on the self-administered Freezing of Gait Questionnaire (FOGQsa), item 3 (Do you feel that your feet get glued to the floor while walking, making a turn or when trying to initiate walking (freez- ing)?) were categorized as having FOG As determined using a prospective falls diary during a 6-month follow-up (see Lindholm et  al. [11] for details) 1 3 Journal of Neurology (2018) 265:1829–1835 1831 As the last step during the outpatient visit, participants Results were instructed to register all consecutive falls and near falls during the following 6 months [17]. They were pro- All 151 participants completed the 10MWT testing. Sam- vided with a diary folder consisting of pre-printed pages ple characteristics are summarized in Table  1. Partici- for recording the date and time of every event and questions pants’ mean (SD) age and PD duration were 68 (9.6) and clarifying whether the incident was a fall. The question was 4 (4) years, respectively; their median (q1–q3) Hoehn and phrased as follows: Did you fall in such a way that your Yahr (HY) stages were II (II–III). Freezing of gait (FOG) body hit the ground? Falls were defined as “an unexpected was experienced by 63 (42%) participants, and 21 (14%) event in which the participants come to rest on the ground, were in HY stage IV or used walking aids during test- floor, or lower level” [17]. The definition of a fall was thor - ing. At the time of assessments, 143 participants (95%) oughly described during the outpatient visit. All participants rated their motor status as “on” or “on with dyskinesias” were telephoned monthly to ensure that registrations had and 8 (5%) rated it as “off”. One hundred forty-six (97%) been completed according to instructions. During the last individuals completed prospective follow-up during the telephone call, they were requested to return the diary folder 6-month period. Forty-seven of those (32%) reported at in a pre-stamped envelope. least one fall and 28 (19%) reported more than one fall. There were statistically significant differences (P < 0.001) in gait speed at all instances in the full group (n = 151). Analyses Absolute mean differences between outcomes from the vari- ous test conditions were generally small, ranging between Data were analysed using IBM SPSS version 22 (IBM Corp., 0.016 and 0.040 m/s (ESs 0.06–0.14) with high levels of Armonk, NY) with the alpha level of significance set at 0.05 agreement (ICC 0.932–0.987) and small measurement errors ( two tailed). Paired sample t tests were used to explore dif- (SEM 0.032–0.076  m/s). Further details are provided in ferences between different standardizations of the 10MWT Table 2. Similar results were also obtained when repeating (ss vs. ds) conducted at t1 and t2, as well as the mean values these analyses among subgroups of individuals with a his- of these (M vs. M ). Similarly, we examined the differ - tory of FOG (n = 63; Table 3) and those in HY stage IV or ss ds ences between trials (t1 vs. t2), and between t1 and mean t1 using walking aids during testing (n = 21; Table 4), as well and t2 values (M ) for ss and ds, respectively. Effect sizes as among those who self-rated their motor status as “off” t1, t2 (ESs) were computed using Cohen’s d; ESs were interpreted during testing (n = 8; data not shown). as small (0.20), moderate (0.50), large (0.80) and very large Forty-seven of 151 participants (32%) reported at least (1.3) [10]. Intra-class correlation (ICC) coefficients (two- one prospective fall during the 6-month follow-up. ROC way mixed effects model, absolute agreement, single meas- curve analyses showed similar discriminate abilities for ure) were calculated to determine the agreement between future falls across the various 10MWT test conditions test conditions, and the standard error of measurement (AUROC, 0.70–0.73). The Youden index ranged between (SEM) was estimated (SD × √[1-ICC]). The analyses were 0.37 and 0.39, with corresponding cut-off points estimated t1 performed for the full sample (n = 151). In addition, explora- at 1.1–1.2 m/s (Table 5). tory subgroup analyses were conducted among (1) people with a history of FOG (n = 63), (2) those in HY stage IV and/ or using walking aids during testing (n = 21), (3) those who self-rated their motor status as “off” during testing (n = 8). Discussion Receiver operating characteristic (ROC) curve analysis was used to determinate optimal gait speed cut-off points We examined the effects of different standardizations of the for prediction of one or more future falls in the full group 10MWT in people with relatively mild PD. Although com- (n = 151). The optimal point is that with the highest true- parisons showed statistically significant differences between positive (sensitivity) and lowest false-positive (1-specific- testing conditions, the sizes of these differences were small ity) values. The areas under the ROC curves (AUROCs) can and the various test results showed high levels of agree- range between 0 and 1, where an AUROC <0.5 indicates ment. The measurement error (SEM) has been suggested that a test performs worse than chance; AUROCs ≥ 0.7 are as a distribution-based minimal important difference (MID) acceptable, with values between 0.7 and 0.9 and >0.9 con- indicator, at and above which differences in outcomes reflect sidered moderate and high, respectively [18, 19]. Values differences of clinical interest [20]. In this study, the SEM (m/s) associated with the highest Youden index (sensitiv- values exceeded absolute mean differences by factors of ity + specificity − 1) were estimated as the optimal cut-off 1.9–2.4. When considering the three subgroups, SEM values points to discriminate between those with and without future exceeded absolute mean differences by factors of up to 23. falls [19]. 1 3 1832 Journal of Neurology (2018) 265:1829–1835 Table 2 Gait speed characteristics according to different standardizations of the 10-m walk test in PD (n = 151) a,b c d a Mean (SD) Mean difference (95% CI) ES ICC (95% CI) SEM Static vs. dynamic start  t1 vs. t1 (n = 150) 1.111 (0.292) vs. 1.094 (0.277) 0.017 (0.08, 0.0259) 0.06 0.980 (0.971, 0.987) 0.041 ss ds  t2 vs. t2 (n = 149) 1.153 (0.298) vs. 1.129 (0.286) 0.024 (0.011, 0.357) 0.08 0.964 (0.946, 0.975) 0.057 ss ds  M vs. M n = 149) 1.132 (0.290) vs. 1.112 (0.278) 0.020 (0.012, 0.028) 0.07 0.983 (0.970, 0.989) 0.037 ss ds ( Static start (n = 150)  t1 vs. t2 1.114 (0.291) vs. 1.154 (0.297) − 0.040 (− 0.057, − 0.024) 0.14 0.932 (0.890, 0.956) 0.076 ss ss  t1 vs. M 1.114 (0.291) vs. 1.134 (0.290) − 0.020 (− 0.028, − 0.012) 0.07 0.982 (0.971, 0.989) 0.039 ss t1,t2 Dynamic start (n = 149)  t1 vs. t2 1.096 (0.277) vs. 1.129 (0.286) − 0.033 (− 0.047, − 0.020) 0.12 0.950 (0.917, 0.968) 0.062 ds ds  t1 vs. M 1.096 (0.277) vs. 1.112 (0.278) − 0.016 (− 0.024, − 0.010) 0.06 0.987 (0.978, 0.992) 0.032 ds t1,t2 PD Parkinson’s disease, m/s meters per second, SD standard deviation, CI confidence interval, ES effect size, ICC intra-class correlation, SEM standard error of measurement (SD × √1– ICC), t1 trial 1 with static start, t1 trial 1 with dynamic start, t2 trial 2 with static start, t2 trial t1 ss ds ss ds 2 with dynamic start, M mean value of trials 1 and 2 with static start, M mean value of trials 1 and 2 with dynamic start, M mean value of ss ds t1,t2 trials 1 and 2 Data are in m/s P < 0.001 in all instances (paired samples t tests) Cohen’ s d (calculated on between-test differences) Two-way mixed effects model (absolute agreement, single measure) Table 3 Gait speed characteristics according to different standardizations of the 10-m walk test in individuals with PD and history of FOG (n = 63) a,b c d a Mean (SD) Mean difference (95% CI) ES ICC (95% CI) SEM Static vs. dynamic start  t1 vs. t1 n = 63) 0.943 (0.284) vs. 0.934 (0.272) 0.009 (− 0.008, 0.022) 0.03 0.977 (0.963, 0.986) 0.043 ss ds (  t2 vs. t2 (n = 62) 0.990 (0.308) vs. 0.971 (0.298) 0.019 (− 0.004, 0.044) 0.06 0.950 (0.918, 0.970) 0.068 ss ds  M vs. M (n = 62) 0.968 (0.293) vs. 0.954 (0.282) 0.014 (− 0.002, 0.029) 0.05 0.977 (0.962, 0.986) 0.044 ss ds Static start (n = 62)  t1 vs. t2 0.945 (0.287) vs. 0.990 (0.308) − 0.045 (− 0.076, − 0.021) 0.15 0.934 (0.867, 0.964) 0.073 ss ss  t1 vs. M 0.945 (0.287) vs. 0.968 (0.293) − 0.023 (− 0.036, − 0.011) 0.08 0.982 (0.963, 0.991) 0.039 ss t1,t2 Dynamic start (n = 62)  t1 vs. t2 0.937 (0.274) vs. 0.971 (0.298) − 0.034 (− 0.058, − 0.008) 0.12 0.937 (0.891, 0.963) 0.068 ds ds  t1 vs. M 0.937 (0.274) vs. 0.954 (0.282) − 0.017 (− 0.029, − 0.004) 0.06 0.983 (0.970, 0.985) 0.036 ds t1,t2 PD Parkinson’s disease, FOG freezing of gait, m/s meters per second, SD standard deviation, CI confidence interval, ES effect size, ICC intra- class correlation, SEM standard error of measurement (SD × √1– ICC), t1 , trial 1 with static start, t1 trial 1 with dynamic start, t2 trial 2 t1 ss ds ss with static start, t2 , trial 2 with dynamic start, M mean value of trials 1 and 2 with static start, M mean value of trials 1 and 2 with dynamic ds ss ds start, M mean value of trials 1 and 2 t1,t2 Data are in m/s P < 0.01 in all instances (paired samples t tests) in all instances but comparisons between static vs. dynamic start (P ≥ 0.082) Cohen’ s d (calculated on between-test differences) Two-way mixed effects model (absolute agreement, single measure) It has been suggested that FOG may affect the outcome Taken together, these observations provide evidence that of the 10MWT [1]. Indeed, individuals with FOG walked observed differences across test conditions can be consid- slower when compared to the whole group. Although we ered clinically trivial. Previous anchor-based MID estimates did not observe any FOG during testing, 10MWT-based gait in non-PD samples have ranged from 0.10 to 0.16 m/s [1]. speed estimates were in agreement across standardizations Taking these estimates into account, the clinical meaning- also among people who reported having FOG. This may fulness of the observed differences diminishes even further. have been due to the use of a start command or straight In accordance with assumptions regarding the mean of walkway during 10MWT. repeated measures obtained under identical conditions as 1 3 Journal of Neurology (2018) 265:1829–1835 1833 Table 4 Gait speed characteristics according to different standardizations of the 10-m walk test in individuals with PD in HY stage IV or using walking aids during testing (n = 21) a,b c d a Mean (SD) Mean difference (95% CI) ES ICC (95% CI) SEM Static vs. dynamic start  t1 vs. t1 (n = 21) 0.700 (0.189) vs. 0.698 (0.154) 0.002 (− 0.029, 0.036) 0.01 0.941 (0.853, 0.977) 0.046 ss ds  t2 vs. t2 (n = 20) 0.722 (0.205) vs. 0.701 (0.160) 0.021 (− 0.015, 0.057) 0.11 0.920 (0.802, 0.969) 0.058 ss ds  M vs. M (n = 20) 0.694 (0.154) vs. 0.706 (0.196) − 0.012 (− 0.021, 0.045) 0.07 0.931(0.829, 0.974) 0.040 ss ds Static start (n = 20)  t1 vs. t2 0.690 (0.189) vs. 0.722 (0.205) − 0.032 (− 0.061, − 0.003) 0.16 0.947 (0.838, 0.981) 0.044 ss ss  t1 vs. M 0.690 (0.190) vs. 0.706 (0.196) − 0.016 (− 0.030, − 0.002) 0.08 0.986 (0.954, 0.995) 0.022 ss t1,t2 Dynamic start (n = 20)  t1 vs. t2 0.688 (0.152) vs. 0.701 (0.160) − 0.013 (− 0.040, 0.013) 0.08 0.943 (0.857, 0.978) 0.036 ds ds  t1 vs. M 0.688 (0.152) vs. 0.695 (0.154) − 0.007 (− 0.020, 0.006) 0.05 0.985 (0.962, 0.994) 0.019 ds t1,t2 PD Parkinson’s disease, HY Hoehn and Yahr stage of PD, m/s meters per second, SD standard deviation, CI confidence interval, ES effect size, ICC intra-class correlation, SEM standard error of measurement (SD × √1– ICC), t1 trial 1 with static start, t1 trial 1 with dynamic start, t1 ss ds t2 trial 2 with static start, t2 trial 2 with dynamic start, M mean value of trials 1 and 2 with static start, M mean value of trials 1 and 2 with ss ds ss ds dynamic start, M mean value of trials 1 and 2 t1,t2 Data are in m/s P ≥ 0.298 in all instances (paired samples t tests) but t2 vs. t2 (static vs. dynamic start; P = 0.031), t1 vs. t2 and t1 vs. M (static start; ss ds ss ss ss t1,t2 P = 0.031) Cohen’ s d (calculated on between-test differences) Two-way mixed effects model (absolute agreement, single measure) Table 5 Discriminant ability of b c d e AUROC (95% CI) Cut-off Sensitivity SpecificityYouden index the 10-m walk test (10MWT) point (m/s) for identification of individuals with prospective falls (n = 146) Static start  t1 0.72 (0.64, 0.81) 1.1 0.70 0.69 0.39  t2 0.72 (0.63, 0.81) 1.2 0.70 0.69 0.39  M 0.73 (0.64, 0.81) 1.1 0.67 0.70 0.37 t1,t2 Dynamic start  t1 0.71 (0.62, 0.80) 1.1 0.72 0.66 0.38  t2 0.70 (0.60, 0.79) 1.1 0.70 0.67 0.37  M 0.70 (0.61, 0.80) 1.1 0.70 0.68 0.38 t1,t2 m/s meters per second, t1 trial 1, t2 trial 2, M mean value of t1 and t2 t1,t2 As determined using a prospective fall diary during a 6-month follow-up (see Lindholm et  al. 2015 for details) Area under the receiver operating characteristic curves of t1, t2 and M during 10MWT with static and t1,t2 dynamic start The proportion of people with prospective falls who had a positive result (scored above the cut-off point) The proportion of people without prospective falls who had a negative result (scored below the cut-off point) Sensitivity + specificity− 1 the best estimate of any measured quantity [7], mean val- practical situations. Similarly, the negligible differences ues from trials 1 and 2 yielded smaller differences, effect between static and dynamic start suggest that the accelera- sizes and SEM values together with larger ICCs than sin- tion distance does not appear to affect the estimated gait gle-observation data from trials 1 and 2. However, given speed considerably. The finding that repeated trials and that the observed differences were very small, it is ques- dynamic start do not appear to have any practical impact tionable if they are of any clinical significance. Therefore, on 10MWT-based outcomes simplifies its conduct and unless there is a specific reason to maximise precision, our should facilitate its use in routine clinical practice. findings suggest that a single trial is sufficient for most 1 3 1834 Journal of Neurology (2018) 265:1829–1835 The observations discussed above were also corrobo- Compliance with ethical standards rated when exploring the implications of different 10MWT Conflicts of interest All authors declare that they have no conflict of standardizations in terms of predicting future falls. The interest. discriminant abilities of both static and dynamic start were very similar for both single trials and mean values. It is also Ethical standard The study was approved by the institutional review noteworthy that trial 1 values and mean (trials 1 and 2) val- board and was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. ues of both static and dynamic start identified 1.1 m/s as an optimal cut-off point. This finding is in line with the sug- gested cut-off point for comfortable gait speed as a predictor Open Access This article is distributed under the terms of the Crea- tive Commons Attribution 4.0 International License (http://creat iveco in the 3-step model [2, 3]. However, while the 3-step model mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- prescribes the use of the mean of two trials, our observations tion, and reproduction in any medium, provided you give appropriate suggest that a single trial with static start will suffice. credit to the original author(s) and the source, provide a link to the Although this study strengthens the current evidence base Creative Commons license, and indicate if changes were made. regarding the conduct of the 10MWT in PD, it has some limitations that should be acknowledged. The study involved people with relatively mild PD, and people above the age of 80 years were not included. Our findings may, therefore, References not be applicable to older people with mild PD and those 1. Bloem BR, Marinus J, Almeida Q, Dibble L, Nieuwboer A, Post in more advanced PD stages. 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Journal of NeurologySpringer Journals

Published: Jun 6, 2018

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