Validity of the Somatic Symptom Disorder–B Criteria Scale (SSD-12) in primary care

Validity of the Somatic Symptom Disorder–B Criteria Scale (SSD-12) in primary care Abstract Aim The Somatic Symptom Disorder–B Criteria Scale (SSD-12) assesses the psychological features of DSM-5 somatic symptom disorder. The purpose of the current study was to investigate the psychometric characteristics and validity of the 12-item instrument to demonstrate its suitability in primary care. Method The study was designed as a cross-sectional survey set in five primary care practices from Munich, Germany (n = 501, 52.0% female, mean age 47 ± 16 years). Item and scale characteristics, as well as measures of reliability and validity, were determined. Results The SSD-12 has good item characteristics and excellent reliability (Cronbach’s α = 0.92). Confirmatory factor analyses provided evidence to support a general factor model of the SSD-12 in primary care (comparative fit index > 0.98, Tucker–Lewis index > 0.98, root mean square error of approximation = 0.090, 90% confidence interval: 0.078–0.102). SSD-12 total sum-score was significantly associated with somatic symptom burden (r = 0.48, P < 0.001), general anxiety (r = 0.54, P < 0.001) and depressive symptoms (r = 0.60, P < 0.001). At the group level, SSD-12 scores could differentiate between different patient groups (e.g. with and without chronic illness). Conclusions The SSD-12 appears to be a reliable, valid and time-efficient self-report measure of the psychological characteristics related to the experience of somatic symptoms which is suitable for primary care. Future research should evaluate its responsiveness to treatment and feasibility as a screening tool in different clinical settings. Diagnosis, medically unexplained symptoms, psychological factors, psychometrics, questionnaires, somatoform disorders Introduction With the release of the Diagnostic and Statistical Manual of Mental Disorders, 5th edition, the diagnostic category of Somatoform Disorders was changed to Somatic Symptom and Related Disorders (SSD) (1). By taking the accumulated knowledge of the last 20 years on pathogenesis, maintenance and prognosis of distressing somatic symptoms into account, DSM-5 has fundamentally shifted the way somatoform disorders are defined, aiming to increase their relevance in the primary care setting (2). While medically unexplained symptoms were a key feature for many of the disorders in DSM-IV (3) and ICD-10 (4), a SSD diagnosis does not require that the patients’ somatic symptoms are medically unexplained. Regardless of their etiology, SSD is characterized by somatic symptoms that are either very distressing or result in significant disruption of functioning (A criterion). In addition, to be diagnosed with SSD, the individual must experience excessive and disproportionate thoughts, feelings and behaviours regarding those symptoms (B criteria) which typically persist at least for 6 months (C criterion). It is believed that ICD-11 will follow a similar approach by introducing the so called ‘bodily distress syndrome’ when it is released (5). Primary care physicians often treat patients with distressing symptoms, such as pain, digestive, cardiovascular or sensory complaints for which there are no biological causes. The symptoms may result from a heightened awareness of certain bodily sensations, combined with a tendency to interpret these sensations as indicators of a medical illness (6). An estimated 20–25% of patients who present with acute somatic symptoms go on to develop a chronic illness. The prevalence of SSD in the general population is estimated to be 5–7% (1), making it one of the most common categories of patient complaints in the primary care setting (7). Many of these patients are significantly impaired by their symptoms and may be subjected to unnecessary testing and procedures, leading to high socio-economic costs (8). Thus, appropriate diagnosis is essential. Self-report questionnaires may assist with the frequent challenge of making a precise assessment in a limited period of time. Although questionnaires alone are insufficient to form the basis of a diagnosis and should always be used in conjunction with a comprehensive clinical evaluation, they are useful to capture the patients’ perception and overall experience of their symptoms. In addition, responses may help to guide discussions about goals and expectations for symptom management (9). There are several well-validated screening questionnaires to determine the presence and severity of a patients’ somatic symptoms (SSD criterion A) [e.g. PHQ-15 (10)]. The Somatic Symptom Disorder–B Criteria Scale (SSD-12) was developed to additionally measure the psychological distress associated with bothersome somatic symptoms (SSD B criteria). Previous studies have shown that the SSD-12 has good reliability and content validity, and is suitable for screening and evaluating psychological aspects of SSD in specialized clinical settings (11). German population-based norms are also available (12). Since the SSD-12 has not yet been applied to general practice, the current study investigated the psychometric characteristics and validity of the instrument within a primary care sample. Methods Participants In a cross-sectional study, the SSD-12 was administered to a convenience primary care sample of 501 patients (52.0% female, mean age 47 ± 16 years) at five primary care practices from Munich, Germany, affiliated to the German Association of Statutory Health Insurance Doctors. Data were collected between October 2015 and April 2016. All consecutive patients who met the inclusion criteria were invited to participate. Inclusion criteria were an age at or above 18 years and the ability to read and understand the German language. Patients who did not attend the practice for a personal consultation or required emergency care were excluded from participation. Fifty of the approached patients did not want to participate. After providing written informed consent, 501 patients completed the presented self-report questionnaires. Table 1 provides characteristics of the sample. Table 1. Demographic characteristics of the primary care sample (2016: Munich, Germany; N = 501) Total (n = 501)    Age in years: mean (SD)  47 (16)  Affiliation to primary care practice in years: mean (SD)  8 (6)    n  %  Sex (female)  259  52.0  Marital status   Married  284  57.1   Unmarried couple (living together)  59  11.9   Single  133  26.8   Widowed  21  4.2  Minimum of one child  332  66.7  Education   No formal qualifications  21  4.2   Up to 10 years of education  321  64.1   More than 10 years of education  145  28.9   Students  14  2.8  Private health insurance  53  10.7  ICPC-2 categories   Respiratory (R)  109  21.8   Musculoskeletal (L)  107  21.4   Process codes (−)  77  15.4   Digestive (D)  39  7.8   Cardiovascular (K)  29  5.8   General and unspecified (A)  28  5.6   Psychological (P)  27  5.4   Other  76  15.1  Most frequent single ICPC-2 codes   Upper respiratory infection acute (R74)  57  11.4   Back syndrome w/o radiating pain (L84)  23  4.6   Blood test (−34)  19  3.8   Gastroenteritis (D73)  17  3.4   Preventive immunization/medication (−44)  15  3.0   Therapeutic counselling (−58)  15  3.0   Neck syndrome (L83)  14  2.8   General symptom/complaint other (A29)  12  2.4   Sinusitis acute/chronic (R75)  10  2.0   Acute bronchitis/bronchiolitis (R78)  9  1.8   Bursitis/tendinitis/synovitis (L87)  8  1.6  At least one self-reported chronic disease (e.g. diabetes or hypertension)  184  36.7  High risk for any psychological disorder (PHQ-15 ≥ 15 or PHQ-9 ≥ 10 or GAD-7 ≥ 10)  123  24.6  High risk for somatization (PHQ-15 ≥ 15)  68  13.6  Total (n = 501)    Age in years: mean (SD)  47 (16)  Affiliation to primary care practice in years: mean (SD)  8 (6)    n  %  Sex (female)  259  52.0  Marital status   Married  284  57.1   Unmarried couple (living together)  59  11.9   Single  133  26.8   Widowed  21  4.2  Minimum of one child  332  66.7  Education   No formal qualifications  21  4.2   Up to 10 years of education  321  64.1   More than 10 years of education  145  28.9   Students  14  2.8  Private health insurance  53  10.7  ICPC-2 categories   Respiratory (R)  109  21.8   Musculoskeletal (L)  107  21.4   Process codes (−)  77  15.4   Digestive (D)  39  7.8   Cardiovascular (K)  29  5.8   General and unspecified (A)  28  5.6   Psychological (P)  27  5.4   Other  76  15.1  Most frequent single ICPC-2 codes   Upper respiratory infection acute (R74)  57  11.4   Back syndrome w/o radiating pain (L84)  23  4.6   Blood test (−34)  19  3.8   Gastroenteritis (D73)  17  3.4   Preventive immunization/medication (−44)  15  3.0   Therapeutic counselling (−58)  15  3.0   Neck syndrome (L83)  14  2.8   General symptom/complaint other (A29)  12  2.4   Sinusitis acute/chronic (R75)  10  2.0   Acute bronchitis/bronchiolitis (R78)  9  1.8   Bursitis/tendinitis/synovitis (L87)  8  1.6  At least one self-reported chronic disease (e.g. diabetes or hypertension)  184  36.7  High risk for any psychological disorder (PHQ-15 ≥ 15 or PHQ-9 ≥ 10 or GAD-7 ≥ 10)  123  24.6  High risk for somatization (PHQ-15 ≥ 15)  68  13.6  Values are absolute frequencies (percentages) or means (SD). View Large Table 1. Demographic characteristics of the primary care sample (2016: Munich, Germany; N = 501) Total (n = 501)    Age in years: mean (SD)  47 (16)  Affiliation to primary care practice in years: mean (SD)  8 (6)    n  %  Sex (female)  259  52.0  Marital status   Married  284  57.1   Unmarried couple (living together)  59  11.9   Single  133  26.8   Widowed  21  4.2  Minimum of one child  332  66.7  Education   No formal qualifications  21  4.2   Up to 10 years of education  321  64.1   More than 10 years of education  145  28.9   Students  14  2.8  Private health insurance  53  10.7  ICPC-2 categories   Respiratory (R)  109  21.8   Musculoskeletal (L)  107  21.4   Process codes (−)  77  15.4   Digestive (D)  39  7.8   Cardiovascular (K)  29  5.8   General and unspecified (A)  28  5.6   Psychological (P)  27  5.4   Other  76  15.1  Most frequent single ICPC-2 codes   Upper respiratory infection acute (R74)  57  11.4   Back syndrome w/o radiating pain (L84)  23  4.6   Blood test (−34)  19  3.8   Gastroenteritis (D73)  17  3.4   Preventive immunization/medication (−44)  15  3.0   Therapeutic counselling (−58)  15  3.0   Neck syndrome (L83)  14  2.8   General symptom/complaint other (A29)  12  2.4   Sinusitis acute/chronic (R75)  10  2.0   Acute bronchitis/bronchiolitis (R78)  9  1.8   Bursitis/tendinitis/synovitis (L87)  8  1.6  At least one self-reported chronic disease (e.g. diabetes or hypertension)  184  36.7  High risk for any psychological disorder (PHQ-15 ≥ 15 or PHQ-9 ≥ 10 or GAD-7 ≥ 10)  123  24.6  High risk for somatization (PHQ-15 ≥ 15)  68  13.6  Total (n = 501)    Age in years: mean (SD)  47 (16)  Affiliation to primary care practice in years: mean (SD)  8 (6)    n  %  Sex (female)  259  52.0  Marital status   Married  284  57.1   Unmarried couple (living together)  59  11.9   Single  133  26.8   Widowed  21  4.2  Minimum of one child  332  66.7  Education   No formal qualifications  21  4.2   Up to 10 years of education  321  64.1   More than 10 years of education  145  28.9   Students  14  2.8  Private health insurance  53  10.7  ICPC-2 categories   Respiratory (R)  109  21.8   Musculoskeletal (L)  107  21.4   Process codes (−)  77  15.4   Digestive (D)  39  7.8   Cardiovascular (K)  29  5.8   General and unspecified (A)  28  5.6   Psychological (P)  27  5.4   Other  76  15.1  Most frequent single ICPC-2 codes   Upper respiratory infection acute (R74)  57  11.4   Back syndrome w/o radiating pain (L84)  23  4.6   Blood test (−34)  19  3.8   Gastroenteritis (D73)  17  3.4   Preventive immunization/medication (−44)  15  3.0   Therapeutic counselling (−58)  15  3.0   Neck syndrome (L83)  14  2.8   General symptom/complaint other (A29)  12  2.4   Sinusitis acute/chronic (R75)  10  2.0   Acute bronchitis/bronchiolitis (R78)  9  1.8   Bursitis/tendinitis/synovitis (L87)  8  1.6  At least one self-reported chronic disease (e.g. diabetes or hypertension)  184  36.7  High risk for any psychological disorder (PHQ-15 ≥ 15 or PHQ-9 ≥ 10 or GAD-7 ≥ 10)  123  24.6  High risk for somatization (PHQ-15 ≥ 15)  68  13.6  Values are absolute frequencies (percentages) or means (SD). View Large Instruments The SSD-12 is composed of 12 items (Supplementary Material A). Each of the three psychological sub-criteria of SSD (cognitive, affective and behavioural aspects associated with bothersome somatic symptoms) is measured by four items with all item scores ranging between 0 (never) and 4 (very often). Previous studies from different settings could show that the SSD-12 has good item characteristics and excellent reliability (Cronbach’s α = 0.95) (11). Using confirmatory factor analyses, both a three-factorial structure which reflects the three psychological criteria of SSD, and a general one-factor model describing psychological distress associated with bothersome somatic symptoms fitted the data well. The SSD-12 total sum-score was closely associated with somatic symptom burden and health anxiety. SSD-12 scores were moderately associated with anxiety and depression. Patients with a higher SSD-12 score reported greater general physical and mental health impairment and significantly higher health care utilization which are key features of patients suffering from somatoform and related disorders (11). Norm values derived from a large sample of the German general population enable comparisons of individual SSD-12 sum-scores with representative data (12). In addition to questions regarding socio-demographic information, other well validated measures to examine the construct validity of the SSD-12 were included in the study. The Patient Health Questionnaire-15 (PHQ-15) (10) assesses the presence and severity of common somatic symptoms (SSD A criterion) within the last 4 weeks using 15 items. Sum-scores range from 0 (not at all) to 30 (very high) and indicate the self-rated symptom burden. We chose this measure because we expect patients with a higher somatic symptom load (PHQ-15) to report a higher psychological burden associated with the symptoms (SSD-12) which should translate into a substantial statistical correlation between the sum-scores of the two instruments. Furthermore, in terms of co-morbidity, somatic symptoms are highly associated with depression and anxiety. Therefore, participants also responded to the Patient Health Questionnaire-9 (PHQ-9) (13) which assesses the presence of the nine DSM criteria for major depression within the last 2 weeks. Scores range from 0 (not at all) to 27 (very high) and indicate the severity of depression. The General Anxiety Disorder-7 (GAD-7) (14) is a self-administered patient questionnaire which is used as a screening tool and severity measure of both generalized anxiety disorder as well as other common anxiety disorders. Scores range from 0 (minimal) to 21 (severe). However, since all three diagnostic concepts (somatoform disorders, depression, anxiety disorders) are considered to be distinct entities, the correlations between the SSD-12 and PHQ-9 and GAD-7 sum-scores were expected to be moderate at best and could then be interpreted in terms of divergent validity. Statistical analyses We computed means, standard deviations and corrected item-total correlations to reflect the psychometric properties of the items. Cronbach’s alpha was determined as a measure of the internal consistency of the scale. To investigate the factorial structure of the questionnaire, we conducted two confirmatory factor analyses (CFA) theoretically derived from a previous study in a clinical population (11): a simple general factor model with all items loading on one ‘general factor’ (the psychological distress associated with bothersome somatic symptoms) and a second ‘three-factor model’ to investigate whether three latent dimensions corresponding to the three sub-criteria of SSD (cognitive, affective, behavioural aspects) could explain the data. Due to the non-normal distribution of our data, robust weighted least squares estimation with mean and variance adjustment (WLSMV) was used to fit the model and missing cases were excluded listwise. The comparative fit index (CFI), Tucker–Lewis index (TLI) and the root mean square error of approximation (RMSEA) were used to test global model fits. Values of RMSEA < 0.60, TLI > 0.95, CFI > 0.95, and SRMR < 0.08 (15) indicate a good fit for continuous data. Construct validity was examined using bivariate correlations between SSD-12, PHQ-15, GAD-7 and PHQ-9. We only included participants who had answered at least 75 % of the items of the respective questionnaires. Mean responses were imputed for any missing data for included participants. To assess the suitability of the SSD-12 for different patient groups, we compared the means of the SSD-12 for patients with and without self-reported chronic disease, at high and low risk of a self-reported psychological disorder (PHQ-15 ≥ 15 or PHQ-9 ≥ 10 or GAD-7 ≥ 10) and at high and low risk of somatization (PHQ-15 ≥ 15). Since patients with either a chronic somatic or psychological disorder are likely to report more bothersome somatic symptoms associated with their disorder (10), we expected them to also score higher in terms of the psychological burden associated with these symptoms (SSD-12 sum-score). Respective frequencies are reported in Table 1. Group comparisons were performed using t-tests (mean) for continuous variables. Tests were considered statistically significant at a two-sided P-value <0.05. Data analyses were conducted using IBM SPSS Statistics 24 and the lavaan package from the statistical computing software R. Results We analyzed data of n = 465 (92.8%) participants who had answered a total of at least 9 of the 12 SSD-12 items (75%). Mean responses were imputed for any additional missing data. Descriptive item statistics The participants responded well to the questionnaire and there was no indication that particular items were skipped or neglected in a systematic way. Responses for every item covered the full range of response categories. Frequency distribution of responses, mean, standard deviation, skewness and item-total-correlations are given in Table 2. We acknowledge the marked skewness of all items which is expected given that the clinical aim is to assess psychological burden in SSD in a primary care setting. Item 10 showed somewhat problematic parameters. It specifies the need for ‘disproportionate’ thoughts about the seriousness of one’s symptoms which seems to be difficult for patients to judge. The internal consistency of the full scale was α = 0.92. Table 2. Frequency distribution of responses (%), means (SD), skewness and item-total correlations for the items of the SSD-12 in the primary care sample (2016: Munich, Germany; N = 501)   Item  Missing  Never (0)  Rarely (1)  Sometimes (2)  Often (3)  Very often (4)  Mean (SD)  Skew.  CoriT  Cognitive  1  0.4  34.6  34.2  24.5  4.3  1.9  1.0 (1.0)  0.71  0.68  4  0.4  29.2  24.3  27.1  14.2  4.7  1.4 (1.2)  0.38  0.67  7  1.7  53.1  22.2  16.1  4.9  1.9  0.8 (1.0)  1.18  0.31  10  0.4  66.2  17.6  13.1  1.9  0.6  0.5 (0.8)  1.54  0.44  Affective  2  0.2  20.0  38.5  29.9  9.0  2.4  1.4 (1.0)  0.45  0.70  5  0.2  36.8  31.0  21.9  7.7  2.4  1.1 (1.1)  0.74  0.81  8  0.4  48.0  23.9  18.1  6.7  3.0  0.9 (1.1)  1.01  0.75  12  0.2  44.1  31.6  17.4  4.9  1.7  0.9 (1.1)  0.88  0.81  Behavioural  3  0.2  39.4  32.7  18.3  7.1  2.4  1.0 (1.0)  0.89  0.77  6  0.4  50.1  32.5  9.5  5.6  1.9  0.8 (1.0)  1.37  0.76  9  0.4  55.3  23.7  14.2  4.1  2.4  0.7 (1.0)  1.35  0.79  11  0.4  44.5  24.5  21.1  6.7  2.8  1.0 (1.0)  1.00  0.69    Item  Missing  Never (0)  Rarely (1)  Sometimes (2)  Often (3)  Very often (4)  Mean (SD)  Skew.  CoriT  Cognitive  1  0.4  34.6  34.2  24.5  4.3  1.9  1.0 (1.0)  0.71  0.68  4  0.4  29.2  24.3  27.1  14.2  4.7  1.4 (1.2)  0.38  0.67  7  1.7  53.1  22.2  16.1  4.9  1.9  0.8 (1.0)  1.18  0.31  10  0.4  66.2  17.6  13.1  1.9  0.6  0.5 (0.8)  1.54  0.44  Affective  2  0.2  20.0  38.5  29.9  9.0  2.4  1.4 (1.0)  0.45  0.70  5  0.2  36.8  31.0  21.9  7.7  2.4  1.1 (1.1)  0.74  0.81  8  0.4  48.0  23.9  18.1  6.7  3.0  0.9 (1.1)  1.01  0.75  12  0.2  44.1  31.6  17.4  4.9  1.7  0.9 (1.1)  0.88  0.81  Behavioural  3  0.2  39.4  32.7  18.3  7.1  2.4  1.0 (1.0)  0.89  0.77  6  0.4  50.1  32.5  9.5  5.6  1.9  0.8 (1.0)  1.37  0.76  9  0.4  55.3  23.7  14.2  4.1  2.4  0.7 (1.0)  1.35  0.79  11  0.4  44.5  24.5  21.1  6.7  2.8  1.0 (1.0)  1.00  0.69  Range for all items = 0–4 (with higher scores representing greater severity); range for complete 12-item scale = 0–48. Skew. = skewness; CoriT = corrected item-total correlations. View Large Table 2. Frequency distribution of responses (%), means (SD), skewness and item-total correlations for the items of the SSD-12 in the primary care sample (2016: Munich, Germany; N = 501)   Item  Missing  Never (0)  Rarely (1)  Sometimes (2)  Often (3)  Very often (4)  Mean (SD)  Skew.  CoriT  Cognitive  1  0.4  34.6  34.2  24.5  4.3  1.9  1.0 (1.0)  0.71  0.68  4  0.4  29.2  24.3  27.1  14.2  4.7  1.4 (1.2)  0.38  0.67  7  1.7  53.1  22.2  16.1  4.9  1.9  0.8 (1.0)  1.18  0.31  10  0.4  66.2  17.6  13.1  1.9  0.6  0.5 (0.8)  1.54  0.44  Affective  2  0.2  20.0  38.5  29.9  9.0  2.4  1.4 (1.0)  0.45  0.70  5  0.2  36.8  31.0  21.9  7.7  2.4  1.1 (1.1)  0.74  0.81  8  0.4  48.0  23.9  18.1  6.7  3.0  0.9 (1.1)  1.01  0.75  12  0.2  44.1  31.6  17.4  4.9  1.7  0.9 (1.1)  0.88  0.81  Behavioural  3  0.2  39.4  32.7  18.3  7.1  2.4  1.0 (1.0)  0.89  0.77  6  0.4  50.1  32.5  9.5  5.6  1.9  0.8 (1.0)  1.37  0.76  9  0.4  55.3  23.7  14.2  4.1  2.4  0.7 (1.0)  1.35  0.79  11  0.4  44.5  24.5  21.1  6.7  2.8  1.0 (1.0)  1.00  0.69    Item  Missing  Never (0)  Rarely (1)  Sometimes (2)  Often (3)  Very often (4)  Mean (SD)  Skew.  CoriT  Cognitive  1  0.4  34.6  34.2  24.5  4.3  1.9  1.0 (1.0)  0.71  0.68  4  0.4  29.2  24.3  27.1  14.2  4.7  1.4 (1.2)  0.38  0.67  7  1.7  53.1  22.2  16.1  4.9  1.9  0.8 (1.0)  1.18  0.31  10  0.4  66.2  17.6  13.1  1.9  0.6  0.5 (0.8)  1.54  0.44  Affective  2  0.2  20.0  38.5  29.9  9.0  2.4  1.4 (1.0)  0.45  0.70  5  0.2  36.8  31.0  21.9  7.7  2.4  1.1 (1.1)  0.74  0.81  8  0.4  48.0  23.9  18.1  6.7  3.0  0.9 (1.1)  1.01  0.75  12  0.2  44.1  31.6  17.4  4.9  1.7  0.9 (1.1)  0.88  0.81  Behavioural  3  0.2  39.4  32.7  18.3  7.1  2.4  1.0 (1.0)  0.89  0.77  6  0.4  50.1  32.5  9.5  5.6  1.9  0.8 (1.0)  1.37  0.76  9  0.4  55.3  23.7  14.2  4.1  2.4  0.7 (1.0)  1.35  0.79  11  0.4  44.5  24.5  21.1  6.7  2.8  1.0 (1.0)  1.00  0.69  Range for all items = 0–4 (with higher scores representing greater severity); range for complete 12-item scale = 0–48. Skew. = skewness; CoriT = corrected item-total correlations. View Large Factorial validity Confirmatory factor analysis revealed good fit indices for a general-factor model [n = 465, CFI = 0.98, TLI = 0.97, RMSEA = 0.098, 90% confidence interval (CI): 0.087–0.109], but also for a model which includes the three latent dimensions as proposed by the theoretical conceptualization of SSD (n = 465, CFI > 0.98, TLI > 0.98, RMSEA = 0.090, 90% CI: 0.078–0.102). The three factor model is displayed in Figure 1. Given the high correlations between the three sub-criteria (r = 0.92–0.96), there appears to be substantial overlap in content between them. Altogether, the results support, therefore, a general factor model of the SSD-12 in primary care which is also in line with previous results from specialized care and the general population (11,12). Figure 1. View largeDownload slide Path diagram illustrating the three-factor-model estimates (n = 465). Figure 1. View largeDownload slide Path diagram illustrating the three-factor-model estimates (n = 465). Construct validity Given the evidence to suggest the general factor model of the SSD-12 is appropriate, an overall sum-score of the SSD-12 was calculated for further analyses. The SSD-12 sum score was significantly correlated with other well-established scales which are evidence of construct validity, that is the PHQ-15 (somatic symptom burden), the PHQ-9 depression scores and the GAD-7 anxiety scores. Note however, that the relatively high correlations with anxiety and depression can also suggest problems in terms of discriminative validity. The series of correlational analyses are shown in Table 3. Table 3. Descriptive characteristics and Pearson correlations between SSD-12 sum-score and other scales in the primary care sample (2016: Munich, Germany; N = 501) Descriptive characteristics  SSD-12  PHQ-15  PHQ-9  GAD-7  N  465  424  462  464  Mean (SD)  11.43 (8.97)  4.74 (4.03)  5.10 (4.86)  3.91 (4.08)  Range  0–47  0–26  0–27  0–21  Correlation with SSD-12 score   Correlation co-efficient (r)    0.48  0.60  0.54  Descriptive characteristics  SSD-12  PHQ-15  PHQ-9  GAD-7  N  465  424  462  464  Mean (SD)  11.43 (8.97)  4.74 (4.03)  5.10 (4.86)  3.91 (4.08)  Range  0–47  0–26  0–27  0–21  Correlation with SSD-12 score   Correlation co-efficient (r)    0.48  0.60  0.54  SSD-12, Somatic Symptom Disorder–B Criterion; PHQ-15, Patient Health Questionnaire Somatic Symptom Scale–15; PHQ-9, Patient Health Questionnaire Depression Scale–9; GAD-7, Generalized Anxiety Disorder Scale–7. All tests were significant after applying a Bonferroni adjustment for multiple testing. View Large Table 3. Descriptive characteristics and Pearson correlations between SSD-12 sum-score and other scales in the primary care sample (2016: Munich, Germany; N = 501) Descriptive characteristics  SSD-12  PHQ-15  PHQ-9  GAD-7  N  465  424  462  464  Mean (SD)  11.43 (8.97)  4.74 (4.03)  5.10 (4.86)  3.91 (4.08)  Range  0–47  0–26  0–27  0–21  Correlation with SSD-12 score   Correlation co-efficient (r)    0.48  0.60  0.54  Descriptive characteristics  SSD-12  PHQ-15  PHQ-9  GAD-7  N  465  424  462  464  Mean (SD)  11.43 (8.97)  4.74 (4.03)  5.10 (4.86)  3.91 (4.08)  Range  0–47  0–26  0–27  0–21  Correlation with SSD-12 score   Correlation co-efficient (r)    0.48  0.60  0.54  SSD-12, Somatic Symptom Disorder–B Criterion; PHQ-15, Patient Health Questionnaire Somatic Symptom Scale–15; PHQ-9, Patient Health Questionnaire Depression Scale–9; GAD-7, Generalized Anxiety Disorder Scale–7. All tests were significant after applying a Bonferroni adjustment for multiple testing. View Large Differential validity The comparison of the average SSD-12 scores from different patient groups (with and without chronic disease, with and without an indication of at least one psychological disorder and with and without indication of somatization) showed that the patients who suffer from a chronic disease (i.e. diabetes or hypertension) reported significantly higher SSD-12 scores than the patients without self-reported chronic disease. The same is true for patients with an indication of at least one psychological disorder or, more specifically, with somatization. Whereas the effect size measuring the differences in SSD-12 scores for patients with and without a chronic disease is rather small (d = 0.44), the differences in SSD-12 scores for patients with and without psychological disorders resulted in large effect sizes (d = 1.29 and 1.35, respectively). The comparison of the average SSD-12 scores from the different patient groups and the corresponding effect sizes are shown in Figure 2. Figure 2. View largeDownload slide Average SSD-12 sum-scores in different patient sub-groups from general practice. Figure 2. View largeDownload slide Average SSD-12 sum-scores in different patient sub-groups from general practice. Discussion The main aim of this study was to assess the usefulness and validity of the SSD-12 to measure the psychological characteristics of SSD in primary care. While there is already some evidence that supports the validity of the scale in specialized care and in the general population (11,12), it had not been applied to a primary care setting. Primary care practitioners represent an integral part of mental health care. As the patients’ usual first point of contact within the health care system, they not only connect patients to secondary and specialist services, but also have the unique opportunity to comprehensively evaluate the patients’ health and psychosocial context (16). The changes to the DSM-5 (and expected ICD-11) diagnostic criteria create a great opportunity to address the problem of under-diagnosis of somatoform disorders in the past. By emphasizing the psychological aspects associated with persistent somatic symptoms, it is possible that the new criteria may be more widely applied. This is especially likely as the diagnosis no longer relies on the idea that symptoms are ‘medically unexplained’. Previously, such uncertainty as to the cause of the symptoms often created unease in physicians who must balance the necessity of ruling out serious illness and increasing chronicity against the cost and distress of extensive testing (17). Primary care practitioners have the competing demands to treat and manage all or most of the patient’s acute and chronic conditions as well as providing preventive health care (17). Such competing demands create particular challenges for which the implementation of screening methods for mental disorders might be useful. This is particularly true as screening methods are time efficient and can open a discussion regarding the patient’s mental health. Since the vast majority of individuals with mental disorders never present to a mental health professional, mental health care is often undertaken at primary care (18). Therefore, there is a growing impetus to incorporate patient-reported outcome measures of symptoms and psychological distress into clinical practice (9). The SSD-12 could be a useful tool to assess psychological burden associated with bothersome somatic symptoms in primary care. Completion of the scale takes approximately 2–3 minutes, and the scoring is easily done within another minute. Its items are easy to understand and it measures a clear construct that patients feel is important to them (11). In the current study, the scale showed a high internal consistency and good item characteristics, apart from one item which showed somewhat problematic parameters. The disproportion of thoughts about the seriousness of one’s symptoms is very difficult for patients to judge themselves, but also for clinicians, especially since SSD can now also be accompanied by known diagnoses of somatic illness. Item 10 was explicitly included to reflect the opinions of physicians. This is in line with the Structured Clinical Interview for DSM-5 (SCID-5) (19), but its inclusion is at the expense of a higher heterogeneity of the scale. Confirmatory factor analyses performed on a ‘three latent dimensions’ model and on a ‘general-factor’ model both fit the data in an acceptable way. The calculation of three sub-scores is more in line with the structure of the DSM-5 criteria and this model might, therefore, be of greater importance for clinical purposes. However, since the three sub-criteria were demonstrably highly correlated in the current sample (Figure 1), a one-factor model suggestive of an overarching psychological burden factor should be favoured. This is in line with previous results from the general population (12). The high correlations between the three sub-criteria should further be discussed in the future. At this stage, it remains unclear whether these three DSM-5 suggested psychological aspects are the most valid, sensitive, and specific empirically founded features in patients with SSD (20). Accordingly, the SSD-12 total sum-score was used for the subsequent validation analyses: increases in total item scores represent increases in the general psychological burden associated with the somatic symptoms. The analysis revealed strong evidence of statistical associations with other measures. Since the psychological dimensions should, by definition, be highly associated with somatic symptom burden, bivariate correlations of SSD-12 and PHQ-15 sum-scores were conducted. The substantial association between the scales (r = 0.48) suggests that patients with a higher physical symptom load tend to report higher psychological burden. The correlations with GAD-7 and PHQ-9 were r = 0.54 and r = 0.60, respectively. These findings are plausible considering the high co-morbidity and partial overlap of somatoform, anxiety and depressive symptoms (21). This overlap is sometimes referred to as the somatization-anxiety-depression-triad, meaning that most patients experience combinations of these symptoms. It is fair to assume that the psychological burden associated with bothersome somatic symptoms is highly intertwined with anxiety and depressive symptoms. Nevertheless, studies show that these symptoms have independent, additive and differential effects on multiple domains of health-related quality of life, functional status, disability and health care use which, therefore, gives support to the differentiation of the three symptom domains (21). Patients who suffer from a chronic disease (i.e. diabetes or hypertension) reported significantly higher SSD-12 scores than patients without self-reported chronic diseases. The same is true for patients with an indication of at least one psychological disorder and, more specifically, somatization. They reported a higher level of psychological distress experienced through their somatic symptoms which means that at group level, the SSD-12 was found to be appropriate to differentiate between the respective patient groups. In contrast to the DSM-5 proposal of SSD, which sums up very heterogeneous patient groups, these results may indicate the importance to calculate separate norms for different patient groups (e.g. patients with or without accompanying serious physical disease, with mono- or poly-symptomatic disorder, with pain or illness anxiety disorder in particular). However, these results are to be considered in the context of patients’ self-reported data which is also one of the few limitations of the study: The diagnostic process did not include a ‘gold-standard’ diagnostic interview or another clinical evaluation to confirm the presence of psychiatric or somatic chronic disorders. Another limitation is that, so far, the SSD-12 does not provide a complete assessment of all DSM-5 criteria for SSD: it only covers the psychological B criteria. Criterion A can be assessed by using the PHQ-15 as a measure of somatic symptom severity, but DSM-5 also requires a ‘chronicity’ criterion (C) and allows the coding of specifiers like the presence of predominant pain, a persistent course with severe symptoms or marked impairment (1). In the future, the combined usage of the PHQ-15 and SSD-12 should be evaluated to ensure their applicability as screening instruments for somatic symptom disorder in primary care. For this purpose, longitudinal data on the SSD-12 is also needed to determine the scale’s test–retest reliability, its responsiveness to treatment and its minimum clinically important difference. So far, the current results indicate that administration of the SSD-12 immediately prior to a primary care consultation could be useful to facilitate patient-centred communication and shared decision making. While patients and providers may, for example disagree on the value of focusing on symptom severity as the main or only goal of treatment, they may be able to align on the common goal of reducing how much the symptoms are dominating a patient’s life which may also serve as a potential direct leverage point for psychological treatment. We believe that the SSD-12 will in the future be helpful in evaluating and monitoring patients’ psychological burden associated with persistent somatic symptoms and in the screening process for somatic symptom and related disorders, so that an earlier detection as well as more effective and quality of life-related interventions can be offered to patients suffering from persistent somatic symptoms. Supplementary material Supplementary data are available at Family Practice online. Declaration Funding: none. Ethical approval: the ethics board of the Medical Faculty of the Technical University of Munich (335/15). Conflicts of interest: none. Acknowledgements We would like to thank the patients, practitioners and staff from the primary care practices who gave their time to take part in this study. The data used for the analyses presented were collected for the MD thesis of Simon Kehrer at the Medical Faculty of the Technical University of Munich. References 1. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders (DSM-5) , 5th edn. Arlington, VA: American Psychiatric Association, 2013. 2. Dimsdale JE, Creed F, Escobar Jet al.   Somatic symptom disorder: an important change in DSM. J Psychosom Res  2013; 75: 223– 8. Google Scholar CrossRef Search ADS PubMed  3. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) . 4th edn, text revision. Washington, DC: American Psychiatric Association, 2000. 4. World Health Organization. The ICD-10 Classification of Mental and Behavioural Disorders: Clinical Descriptions and Diagnostic Guidelines . 10th edn. Geneva: World Health Organization, 1992. 5. Gureje O, Reed GM. Bodily distress disorder in ICD-11: problems and prospects. World Psychiatry  2016; 15: 291– 2. Google Scholar CrossRef Search ADS PubMed  6. Kurlansik SL, Maffei MS. Somatic symptom disorder. Am Fam Physician  2016; 93: 49– 54. Google Scholar PubMed  7. Hatcher S, Arroll B. Assessment and management of medically unexplained symptoms. BMJ  2008; 336: 1124– 8. Google Scholar CrossRef Search ADS PubMed  8. Jacobi F, Wittchen H-U, Holting Cet al.   Prevalence, co-morbidity and correlates of mental disorders in the general population: results from the German Health Interview and Examination Survey (GHS). Psychol Med  2004; 34: 597– 611. Google Scholar CrossRef Search ADS PubMed  9. Black N. Patient reported outcome measures could help transform healthcare. BMJ  2013; 346: f167. Google Scholar CrossRef Search ADS PubMed  10. Kroenke K, Spitzer RL, Williams JB. The PHQ-15: validity of a new measure for evaluating the severity of somatic symptoms. Psychosom Med  2002; 64: 258– 66. Google Scholar CrossRef Search ADS PubMed  11. Toussaint A, Murray AM, Voigt Ket al.   Development and validation of the Somatic Symptom Disorder–B Criteria Scale (SSD-12). Psychosom Med  2016; 78: 5– 12. Google Scholar CrossRef Search ADS PubMed  12. Toussaint A, Löwe B, Brähler E, Jordan P. The Somatic Symptom Disorder–B Criteria Scale (SSD-12): factorial structure, validity and population-based norms. J Psychosom Res  2017; 97: 9– 17. Google Scholar CrossRef Search ADS PubMed  13. Kroenke K, Spitzer RL, Williams JB. The PHQ-9: validity of a brief depression severity measure. J Gen Intern Med  2001; 16: 606– 13. Google Scholar CrossRef Search ADS PubMed  14. Löwe B, Decker O, Müller Set al.   Validation and standardization of the Generalized Anxiety Disorder Screener (GAD-7) in the general population. Med Care  2008; 46: 266– 74. Google Scholar CrossRef Search ADS PubMed  15. Schreiber JB, Nora A, Stage FK, Barlow EA, King J. Reporting structural equation modeling and confirmatory factor analysis results: a review. J Educ Res  2006; 99: 323– 37. Google Scholar CrossRef Search ADS   16. Starfield B. Is primary care essential? Lancet  1994; 344: 1129– 33. Google Scholar CrossRef Search ADS PubMed  17. Murray AM, Toussaint A, Althaus A, Löwe B. The challenge of diagnosing non-specific, functional, and somatoform disorders: a systematic review of barriers to diagnosis in primary care. J Psychosom Res  2016; 80: 1– 10. Google Scholar CrossRef Search ADS PubMed  18. Rief W, Martin A, Klaiberg A, Brähler E. Specific effects of depression, panic, and somatic symptoms on illness behavior. Psychosom Med  2005; 67: 596– 601. Google Scholar CrossRef Search ADS PubMed  19. First MB, Williams JBW, Karg RS, Spitzer RL. Structured Clinical Interview for DSM-5—Research Version (SCID-5 for DSM-5, Research Version; SCID-5-RV) . Arlington, VA: American Psychiatric Association, 2015. 20. Rief W, Martin A. How to use the new DSM-5 somatic symptom disorder diagnosis in research and practice: a critical evaluation and a proposal for modifications. Annu Rev Clin Psychol  2014; 10: 339– 67. Google Scholar CrossRef Search ADS PubMed  21. Kohlmann S, Gierk B, Hilbert A, Brähler E, Löwe B. The overlap of somatic, anxious and depressive syndromes. J Psychosom Res  2016; 90: 51– 6. Google Scholar CrossRef Search ADS PubMed  © The Author(s) 2017. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Family Practice Oxford University Press

Validity of the Somatic Symptom Disorder–B Criteria Scale (SSD-12) in primary care

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Abstract

Abstract Aim The Somatic Symptom Disorder–B Criteria Scale (SSD-12) assesses the psychological features of DSM-5 somatic symptom disorder. The purpose of the current study was to investigate the psychometric characteristics and validity of the 12-item instrument to demonstrate its suitability in primary care. Method The study was designed as a cross-sectional survey set in five primary care practices from Munich, Germany (n = 501, 52.0% female, mean age 47 ± 16 years). Item and scale characteristics, as well as measures of reliability and validity, were determined. Results The SSD-12 has good item characteristics and excellent reliability (Cronbach’s α = 0.92). Confirmatory factor analyses provided evidence to support a general factor model of the SSD-12 in primary care (comparative fit index > 0.98, Tucker–Lewis index > 0.98, root mean square error of approximation = 0.090, 90% confidence interval: 0.078–0.102). SSD-12 total sum-score was significantly associated with somatic symptom burden (r = 0.48, P < 0.001), general anxiety (r = 0.54, P < 0.001) and depressive symptoms (r = 0.60, P < 0.001). At the group level, SSD-12 scores could differentiate between different patient groups (e.g. with and without chronic illness). Conclusions The SSD-12 appears to be a reliable, valid and time-efficient self-report measure of the psychological characteristics related to the experience of somatic symptoms which is suitable for primary care. Future research should evaluate its responsiveness to treatment and feasibility as a screening tool in different clinical settings. Diagnosis, medically unexplained symptoms, psychological factors, psychometrics, questionnaires, somatoform disorders Introduction With the release of the Diagnostic and Statistical Manual of Mental Disorders, 5th edition, the diagnostic category of Somatoform Disorders was changed to Somatic Symptom and Related Disorders (SSD) (1). By taking the accumulated knowledge of the last 20 years on pathogenesis, maintenance and prognosis of distressing somatic symptoms into account, DSM-5 has fundamentally shifted the way somatoform disorders are defined, aiming to increase their relevance in the primary care setting (2). While medically unexplained symptoms were a key feature for many of the disorders in DSM-IV (3) and ICD-10 (4), a SSD diagnosis does not require that the patients’ somatic symptoms are medically unexplained. Regardless of their etiology, SSD is characterized by somatic symptoms that are either very distressing or result in significant disruption of functioning (A criterion). In addition, to be diagnosed with SSD, the individual must experience excessive and disproportionate thoughts, feelings and behaviours regarding those symptoms (B criteria) which typically persist at least for 6 months (C criterion). It is believed that ICD-11 will follow a similar approach by introducing the so called ‘bodily distress syndrome’ when it is released (5). Primary care physicians often treat patients with distressing symptoms, such as pain, digestive, cardiovascular or sensory complaints for which there are no biological causes. The symptoms may result from a heightened awareness of certain bodily sensations, combined with a tendency to interpret these sensations as indicators of a medical illness (6). An estimated 20–25% of patients who present with acute somatic symptoms go on to develop a chronic illness. The prevalence of SSD in the general population is estimated to be 5–7% (1), making it one of the most common categories of patient complaints in the primary care setting (7). Many of these patients are significantly impaired by their symptoms and may be subjected to unnecessary testing and procedures, leading to high socio-economic costs (8). Thus, appropriate diagnosis is essential. Self-report questionnaires may assist with the frequent challenge of making a precise assessment in a limited period of time. Although questionnaires alone are insufficient to form the basis of a diagnosis and should always be used in conjunction with a comprehensive clinical evaluation, they are useful to capture the patients’ perception and overall experience of their symptoms. In addition, responses may help to guide discussions about goals and expectations for symptom management (9). There are several well-validated screening questionnaires to determine the presence and severity of a patients’ somatic symptoms (SSD criterion A) [e.g. PHQ-15 (10)]. The Somatic Symptom Disorder–B Criteria Scale (SSD-12) was developed to additionally measure the psychological distress associated with bothersome somatic symptoms (SSD B criteria). Previous studies have shown that the SSD-12 has good reliability and content validity, and is suitable for screening and evaluating psychological aspects of SSD in specialized clinical settings (11). German population-based norms are also available (12). Since the SSD-12 has not yet been applied to general practice, the current study investigated the psychometric characteristics and validity of the instrument within a primary care sample. Methods Participants In a cross-sectional study, the SSD-12 was administered to a convenience primary care sample of 501 patients (52.0% female, mean age 47 ± 16 years) at five primary care practices from Munich, Germany, affiliated to the German Association of Statutory Health Insurance Doctors. Data were collected between October 2015 and April 2016. All consecutive patients who met the inclusion criteria were invited to participate. Inclusion criteria were an age at or above 18 years and the ability to read and understand the German language. Patients who did not attend the practice for a personal consultation or required emergency care were excluded from participation. Fifty of the approached patients did not want to participate. After providing written informed consent, 501 patients completed the presented self-report questionnaires. Table 1 provides characteristics of the sample. Table 1. Demographic characteristics of the primary care sample (2016: Munich, Germany; N = 501) Total (n = 501)    Age in years: mean (SD)  47 (16)  Affiliation to primary care practice in years: mean (SD)  8 (6)    n  %  Sex (female)  259  52.0  Marital status   Married  284  57.1   Unmarried couple (living together)  59  11.9   Single  133  26.8   Widowed  21  4.2  Minimum of one child  332  66.7  Education   No formal qualifications  21  4.2   Up to 10 years of education  321  64.1   More than 10 years of education  145  28.9   Students  14  2.8  Private health insurance  53  10.7  ICPC-2 categories   Respiratory (R)  109  21.8   Musculoskeletal (L)  107  21.4   Process codes (−)  77  15.4   Digestive (D)  39  7.8   Cardiovascular (K)  29  5.8   General and unspecified (A)  28  5.6   Psychological (P)  27  5.4   Other  76  15.1  Most frequent single ICPC-2 codes   Upper respiratory infection acute (R74)  57  11.4   Back syndrome w/o radiating pain (L84)  23  4.6   Blood test (−34)  19  3.8   Gastroenteritis (D73)  17  3.4   Preventive immunization/medication (−44)  15  3.0   Therapeutic counselling (−58)  15  3.0   Neck syndrome (L83)  14  2.8   General symptom/complaint other (A29)  12  2.4   Sinusitis acute/chronic (R75)  10  2.0   Acute bronchitis/bronchiolitis (R78)  9  1.8   Bursitis/tendinitis/synovitis (L87)  8  1.6  At least one self-reported chronic disease (e.g. diabetes or hypertension)  184  36.7  High risk for any psychological disorder (PHQ-15 ≥ 15 or PHQ-9 ≥ 10 or GAD-7 ≥ 10)  123  24.6  High risk for somatization (PHQ-15 ≥ 15)  68  13.6  Total (n = 501)    Age in years: mean (SD)  47 (16)  Affiliation to primary care practice in years: mean (SD)  8 (6)    n  %  Sex (female)  259  52.0  Marital status   Married  284  57.1   Unmarried couple (living together)  59  11.9   Single  133  26.8   Widowed  21  4.2  Minimum of one child  332  66.7  Education   No formal qualifications  21  4.2   Up to 10 years of education  321  64.1   More than 10 years of education  145  28.9   Students  14  2.8  Private health insurance  53  10.7  ICPC-2 categories   Respiratory (R)  109  21.8   Musculoskeletal (L)  107  21.4   Process codes (−)  77  15.4   Digestive (D)  39  7.8   Cardiovascular (K)  29  5.8   General and unspecified (A)  28  5.6   Psychological (P)  27  5.4   Other  76  15.1  Most frequent single ICPC-2 codes   Upper respiratory infection acute (R74)  57  11.4   Back syndrome w/o radiating pain (L84)  23  4.6   Blood test (−34)  19  3.8   Gastroenteritis (D73)  17  3.4   Preventive immunization/medication (−44)  15  3.0   Therapeutic counselling (−58)  15  3.0   Neck syndrome (L83)  14  2.8   General symptom/complaint other (A29)  12  2.4   Sinusitis acute/chronic (R75)  10  2.0   Acute bronchitis/bronchiolitis (R78)  9  1.8   Bursitis/tendinitis/synovitis (L87)  8  1.6  At least one self-reported chronic disease (e.g. diabetes or hypertension)  184  36.7  High risk for any psychological disorder (PHQ-15 ≥ 15 or PHQ-9 ≥ 10 or GAD-7 ≥ 10)  123  24.6  High risk for somatization (PHQ-15 ≥ 15)  68  13.6  Values are absolute frequencies (percentages) or means (SD). View Large Table 1. Demographic characteristics of the primary care sample (2016: Munich, Germany; N = 501) Total (n = 501)    Age in years: mean (SD)  47 (16)  Affiliation to primary care practice in years: mean (SD)  8 (6)    n  %  Sex (female)  259  52.0  Marital status   Married  284  57.1   Unmarried couple (living together)  59  11.9   Single  133  26.8   Widowed  21  4.2  Minimum of one child  332  66.7  Education   No formal qualifications  21  4.2   Up to 10 years of education  321  64.1   More than 10 years of education  145  28.9   Students  14  2.8  Private health insurance  53  10.7  ICPC-2 categories   Respiratory (R)  109  21.8   Musculoskeletal (L)  107  21.4   Process codes (−)  77  15.4   Digestive (D)  39  7.8   Cardiovascular (K)  29  5.8   General and unspecified (A)  28  5.6   Psychological (P)  27  5.4   Other  76  15.1  Most frequent single ICPC-2 codes   Upper respiratory infection acute (R74)  57  11.4   Back syndrome w/o radiating pain (L84)  23  4.6   Blood test (−34)  19  3.8   Gastroenteritis (D73)  17  3.4   Preventive immunization/medication (−44)  15  3.0   Therapeutic counselling (−58)  15  3.0   Neck syndrome (L83)  14  2.8   General symptom/complaint other (A29)  12  2.4   Sinusitis acute/chronic (R75)  10  2.0   Acute bronchitis/bronchiolitis (R78)  9  1.8   Bursitis/tendinitis/synovitis (L87)  8  1.6  At least one self-reported chronic disease (e.g. diabetes or hypertension)  184  36.7  High risk for any psychological disorder (PHQ-15 ≥ 15 or PHQ-9 ≥ 10 or GAD-7 ≥ 10)  123  24.6  High risk for somatization (PHQ-15 ≥ 15)  68  13.6  Total (n = 501)    Age in years: mean (SD)  47 (16)  Affiliation to primary care practice in years: mean (SD)  8 (6)    n  %  Sex (female)  259  52.0  Marital status   Married  284  57.1   Unmarried couple (living together)  59  11.9   Single  133  26.8   Widowed  21  4.2  Minimum of one child  332  66.7  Education   No formal qualifications  21  4.2   Up to 10 years of education  321  64.1   More than 10 years of education  145  28.9   Students  14  2.8  Private health insurance  53  10.7  ICPC-2 categories   Respiratory (R)  109  21.8   Musculoskeletal (L)  107  21.4   Process codes (−)  77  15.4   Digestive (D)  39  7.8   Cardiovascular (K)  29  5.8   General and unspecified (A)  28  5.6   Psychological (P)  27  5.4   Other  76  15.1  Most frequent single ICPC-2 codes   Upper respiratory infection acute (R74)  57  11.4   Back syndrome w/o radiating pain (L84)  23  4.6   Blood test (−34)  19  3.8   Gastroenteritis (D73)  17  3.4   Preventive immunization/medication (−44)  15  3.0   Therapeutic counselling (−58)  15  3.0   Neck syndrome (L83)  14  2.8   General symptom/complaint other (A29)  12  2.4   Sinusitis acute/chronic (R75)  10  2.0   Acute bronchitis/bronchiolitis (R78)  9  1.8   Bursitis/tendinitis/synovitis (L87)  8  1.6  At least one self-reported chronic disease (e.g. diabetes or hypertension)  184  36.7  High risk for any psychological disorder (PHQ-15 ≥ 15 or PHQ-9 ≥ 10 or GAD-7 ≥ 10)  123  24.6  High risk for somatization (PHQ-15 ≥ 15)  68  13.6  Values are absolute frequencies (percentages) or means (SD). View Large Instruments The SSD-12 is composed of 12 items (Supplementary Material A). Each of the three psychological sub-criteria of SSD (cognitive, affective and behavioural aspects associated with bothersome somatic symptoms) is measured by four items with all item scores ranging between 0 (never) and 4 (very often). Previous studies from different settings could show that the SSD-12 has good item characteristics and excellent reliability (Cronbach’s α = 0.95) (11). Using confirmatory factor analyses, both a three-factorial structure which reflects the three psychological criteria of SSD, and a general one-factor model describing psychological distress associated with bothersome somatic symptoms fitted the data well. The SSD-12 total sum-score was closely associated with somatic symptom burden and health anxiety. SSD-12 scores were moderately associated with anxiety and depression. Patients with a higher SSD-12 score reported greater general physical and mental health impairment and significantly higher health care utilization which are key features of patients suffering from somatoform and related disorders (11). Norm values derived from a large sample of the German general population enable comparisons of individual SSD-12 sum-scores with representative data (12). In addition to questions regarding socio-demographic information, other well validated measures to examine the construct validity of the SSD-12 were included in the study. The Patient Health Questionnaire-15 (PHQ-15) (10) assesses the presence and severity of common somatic symptoms (SSD A criterion) within the last 4 weeks using 15 items. Sum-scores range from 0 (not at all) to 30 (very high) and indicate the self-rated symptom burden. We chose this measure because we expect patients with a higher somatic symptom load (PHQ-15) to report a higher psychological burden associated with the symptoms (SSD-12) which should translate into a substantial statistical correlation between the sum-scores of the two instruments. Furthermore, in terms of co-morbidity, somatic symptoms are highly associated with depression and anxiety. Therefore, participants also responded to the Patient Health Questionnaire-9 (PHQ-9) (13) which assesses the presence of the nine DSM criteria for major depression within the last 2 weeks. Scores range from 0 (not at all) to 27 (very high) and indicate the severity of depression. The General Anxiety Disorder-7 (GAD-7) (14) is a self-administered patient questionnaire which is used as a screening tool and severity measure of both generalized anxiety disorder as well as other common anxiety disorders. Scores range from 0 (minimal) to 21 (severe). However, since all three diagnostic concepts (somatoform disorders, depression, anxiety disorders) are considered to be distinct entities, the correlations between the SSD-12 and PHQ-9 and GAD-7 sum-scores were expected to be moderate at best and could then be interpreted in terms of divergent validity. Statistical analyses We computed means, standard deviations and corrected item-total correlations to reflect the psychometric properties of the items. Cronbach’s alpha was determined as a measure of the internal consistency of the scale. To investigate the factorial structure of the questionnaire, we conducted two confirmatory factor analyses (CFA) theoretically derived from a previous study in a clinical population (11): a simple general factor model with all items loading on one ‘general factor’ (the psychological distress associated with bothersome somatic symptoms) and a second ‘three-factor model’ to investigate whether three latent dimensions corresponding to the three sub-criteria of SSD (cognitive, affective, behavioural aspects) could explain the data. Due to the non-normal distribution of our data, robust weighted least squares estimation with mean and variance adjustment (WLSMV) was used to fit the model and missing cases were excluded listwise. The comparative fit index (CFI), Tucker–Lewis index (TLI) and the root mean square error of approximation (RMSEA) were used to test global model fits. Values of RMSEA < 0.60, TLI > 0.95, CFI > 0.95, and SRMR < 0.08 (15) indicate a good fit for continuous data. Construct validity was examined using bivariate correlations between SSD-12, PHQ-15, GAD-7 and PHQ-9. We only included participants who had answered at least 75 % of the items of the respective questionnaires. Mean responses were imputed for any missing data for included participants. To assess the suitability of the SSD-12 for different patient groups, we compared the means of the SSD-12 for patients with and without self-reported chronic disease, at high and low risk of a self-reported psychological disorder (PHQ-15 ≥ 15 or PHQ-9 ≥ 10 or GAD-7 ≥ 10) and at high and low risk of somatization (PHQ-15 ≥ 15). Since patients with either a chronic somatic or psychological disorder are likely to report more bothersome somatic symptoms associated with their disorder (10), we expected them to also score higher in terms of the psychological burden associated with these symptoms (SSD-12 sum-score). Respective frequencies are reported in Table 1. Group comparisons were performed using t-tests (mean) for continuous variables. Tests were considered statistically significant at a two-sided P-value <0.05. Data analyses were conducted using IBM SPSS Statistics 24 and the lavaan package from the statistical computing software R. Results We analyzed data of n = 465 (92.8%) participants who had answered a total of at least 9 of the 12 SSD-12 items (75%). Mean responses were imputed for any additional missing data. Descriptive item statistics The participants responded well to the questionnaire and there was no indication that particular items were skipped or neglected in a systematic way. Responses for every item covered the full range of response categories. Frequency distribution of responses, mean, standard deviation, skewness and item-total-correlations are given in Table 2. We acknowledge the marked skewness of all items which is expected given that the clinical aim is to assess psychological burden in SSD in a primary care setting. Item 10 showed somewhat problematic parameters. It specifies the need for ‘disproportionate’ thoughts about the seriousness of one’s symptoms which seems to be difficult for patients to judge. The internal consistency of the full scale was α = 0.92. Table 2. Frequency distribution of responses (%), means (SD), skewness and item-total correlations for the items of the SSD-12 in the primary care sample (2016: Munich, Germany; N = 501)   Item  Missing  Never (0)  Rarely (1)  Sometimes (2)  Often (3)  Very often (4)  Mean (SD)  Skew.  CoriT  Cognitive  1  0.4  34.6  34.2  24.5  4.3  1.9  1.0 (1.0)  0.71  0.68  4  0.4  29.2  24.3  27.1  14.2  4.7  1.4 (1.2)  0.38  0.67  7  1.7  53.1  22.2  16.1  4.9  1.9  0.8 (1.0)  1.18  0.31  10  0.4  66.2  17.6  13.1  1.9  0.6  0.5 (0.8)  1.54  0.44  Affective  2  0.2  20.0  38.5  29.9  9.0  2.4  1.4 (1.0)  0.45  0.70  5  0.2  36.8  31.0  21.9  7.7  2.4  1.1 (1.1)  0.74  0.81  8  0.4  48.0  23.9  18.1  6.7  3.0  0.9 (1.1)  1.01  0.75  12  0.2  44.1  31.6  17.4  4.9  1.7  0.9 (1.1)  0.88  0.81  Behavioural  3  0.2  39.4  32.7  18.3  7.1  2.4  1.0 (1.0)  0.89  0.77  6  0.4  50.1  32.5  9.5  5.6  1.9  0.8 (1.0)  1.37  0.76  9  0.4  55.3  23.7  14.2  4.1  2.4  0.7 (1.0)  1.35  0.79  11  0.4  44.5  24.5  21.1  6.7  2.8  1.0 (1.0)  1.00  0.69    Item  Missing  Never (0)  Rarely (1)  Sometimes (2)  Often (3)  Very often (4)  Mean (SD)  Skew.  CoriT  Cognitive  1  0.4  34.6  34.2  24.5  4.3  1.9  1.0 (1.0)  0.71  0.68  4  0.4  29.2  24.3  27.1  14.2  4.7  1.4 (1.2)  0.38  0.67  7  1.7  53.1  22.2  16.1  4.9  1.9  0.8 (1.0)  1.18  0.31  10  0.4  66.2  17.6  13.1  1.9  0.6  0.5 (0.8)  1.54  0.44  Affective  2  0.2  20.0  38.5  29.9  9.0  2.4  1.4 (1.0)  0.45  0.70  5  0.2  36.8  31.0  21.9  7.7  2.4  1.1 (1.1)  0.74  0.81  8  0.4  48.0  23.9  18.1  6.7  3.0  0.9 (1.1)  1.01  0.75  12  0.2  44.1  31.6  17.4  4.9  1.7  0.9 (1.1)  0.88  0.81  Behavioural  3  0.2  39.4  32.7  18.3  7.1  2.4  1.0 (1.0)  0.89  0.77  6  0.4  50.1  32.5  9.5  5.6  1.9  0.8 (1.0)  1.37  0.76  9  0.4  55.3  23.7  14.2  4.1  2.4  0.7 (1.0)  1.35  0.79  11  0.4  44.5  24.5  21.1  6.7  2.8  1.0 (1.0)  1.00  0.69  Range for all items = 0–4 (with higher scores representing greater severity); range for complete 12-item scale = 0–48. Skew. = skewness; CoriT = corrected item-total correlations. View Large Table 2. Frequency distribution of responses (%), means (SD), skewness and item-total correlations for the items of the SSD-12 in the primary care sample (2016: Munich, Germany; N = 501)   Item  Missing  Never (0)  Rarely (1)  Sometimes (2)  Often (3)  Very often (4)  Mean (SD)  Skew.  CoriT  Cognitive  1  0.4  34.6  34.2  24.5  4.3  1.9  1.0 (1.0)  0.71  0.68  4  0.4  29.2  24.3  27.1  14.2  4.7  1.4 (1.2)  0.38  0.67  7  1.7  53.1  22.2  16.1  4.9  1.9  0.8 (1.0)  1.18  0.31  10  0.4  66.2  17.6  13.1  1.9  0.6  0.5 (0.8)  1.54  0.44  Affective  2  0.2  20.0  38.5  29.9  9.0  2.4  1.4 (1.0)  0.45  0.70  5  0.2  36.8  31.0  21.9  7.7  2.4  1.1 (1.1)  0.74  0.81  8  0.4  48.0  23.9  18.1  6.7  3.0  0.9 (1.1)  1.01  0.75  12  0.2  44.1  31.6  17.4  4.9  1.7  0.9 (1.1)  0.88  0.81  Behavioural  3  0.2  39.4  32.7  18.3  7.1  2.4  1.0 (1.0)  0.89  0.77  6  0.4  50.1  32.5  9.5  5.6  1.9  0.8 (1.0)  1.37  0.76  9  0.4  55.3  23.7  14.2  4.1  2.4  0.7 (1.0)  1.35  0.79  11  0.4  44.5  24.5  21.1  6.7  2.8  1.0 (1.0)  1.00  0.69    Item  Missing  Never (0)  Rarely (1)  Sometimes (2)  Often (3)  Very often (4)  Mean (SD)  Skew.  CoriT  Cognitive  1  0.4  34.6  34.2  24.5  4.3  1.9  1.0 (1.0)  0.71  0.68  4  0.4  29.2  24.3  27.1  14.2  4.7  1.4 (1.2)  0.38  0.67  7  1.7  53.1  22.2  16.1  4.9  1.9  0.8 (1.0)  1.18  0.31  10  0.4  66.2  17.6  13.1  1.9  0.6  0.5 (0.8)  1.54  0.44  Affective  2  0.2  20.0  38.5  29.9  9.0  2.4  1.4 (1.0)  0.45  0.70  5  0.2  36.8  31.0  21.9  7.7  2.4  1.1 (1.1)  0.74  0.81  8  0.4  48.0  23.9  18.1  6.7  3.0  0.9 (1.1)  1.01  0.75  12  0.2  44.1  31.6  17.4  4.9  1.7  0.9 (1.1)  0.88  0.81  Behavioural  3  0.2  39.4  32.7  18.3  7.1  2.4  1.0 (1.0)  0.89  0.77  6  0.4  50.1  32.5  9.5  5.6  1.9  0.8 (1.0)  1.37  0.76  9  0.4  55.3  23.7  14.2  4.1  2.4  0.7 (1.0)  1.35  0.79  11  0.4  44.5  24.5  21.1  6.7  2.8  1.0 (1.0)  1.00  0.69  Range for all items = 0–4 (with higher scores representing greater severity); range for complete 12-item scale = 0–48. Skew. = skewness; CoriT = corrected item-total correlations. View Large Factorial validity Confirmatory factor analysis revealed good fit indices for a general-factor model [n = 465, CFI = 0.98, TLI = 0.97, RMSEA = 0.098, 90% confidence interval (CI): 0.087–0.109], but also for a model which includes the three latent dimensions as proposed by the theoretical conceptualization of SSD (n = 465, CFI > 0.98, TLI > 0.98, RMSEA = 0.090, 90% CI: 0.078–0.102). The three factor model is displayed in Figure 1. Given the high correlations between the three sub-criteria (r = 0.92–0.96), there appears to be substantial overlap in content between them. Altogether, the results support, therefore, a general factor model of the SSD-12 in primary care which is also in line with previous results from specialized care and the general population (11,12). Figure 1. View largeDownload slide Path diagram illustrating the three-factor-model estimates (n = 465). Figure 1. View largeDownload slide Path diagram illustrating the three-factor-model estimates (n = 465). Construct validity Given the evidence to suggest the general factor model of the SSD-12 is appropriate, an overall sum-score of the SSD-12 was calculated for further analyses. The SSD-12 sum score was significantly correlated with other well-established scales which are evidence of construct validity, that is the PHQ-15 (somatic symptom burden), the PHQ-9 depression scores and the GAD-7 anxiety scores. Note however, that the relatively high correlations with anxiety and depression can also suggest problems in terms of discriminative validity. The series of correlational analyses are shown in Table 3. Table 3. Descriptive characteristics and Pearson correlations between SSD-12 sum-score and other scales in the primary care sample (2016: Munich, Germany; N = 501) Descriptive characteristics  SSD-12  PHQ-15  PHQ-9  GAD-7  N  465  424  462  464  Mean (SD)  11.43 (8.97)  4.74 (4.03)  5.10 (4.86)  3.91 (4.08)  Range  0–47  0–26  0–27  0–21  Correlation with SSD-12 score   Correlation co-efficient (r)    0.48  0.60  0.54  Descriptive characteristics  SSD-12  PHQ-15  PHQ-9  GAD-7  N  465  424  462  464  Mean (SD)  11.43 (8.97)  4.74 (4.03)  5.10 (4.86)  3.91 (4.08)  Range  0–47  0–26  0–27  0–21  Correlation with SSD-12 score   Correlation co-efficient (r)    0.48  0.60  0.54  SSD-12, Somatic Symptom Disorder–B Criterion; PHQ-15, Patient Health Questionnaire Somatic Symptom Scale–15; PHQ-9, Patient Health Questionnaire Depression Scale–9; GAD-7, Generalized Anxiety Disorder Scale–7. All tests were significant after applying a Bonferroni adjustment for multiple testing. View Large Table 3. Descriptive characteristics and Pearson correlations between SSD-12 sum-score and other scales in the primary care sample (2016: Munich, Germany; N = 501) Descriptive characteristics  SSD-12  PHQ-15  PHQ-9  GAD-7  N  465  424  462  464  Mean (SD)  11.43 (8.97)  4.74 (4.03)  5.10 (4.86)  3.91 (4.08)  Range  0–47  0–26  0–27  0–21  Correlation with SSD-12 score   Correlation co-efficient (r)    0.48  0.60  0.54  Descriptive characteristics  SSD-12  PHQ-15  PHQ-9  GAD-7  N  465  424  462  464  Mean (SD)  11.43 (8.97)  4.74 (4.03)  5.10 (4.86)  3.91 (4.08)  Range  0–47  0–26  0–27  0–21  Correlation with SSD-12 score   Correlation co-efficient (r)    0.48  0.60  0.54  SSD-12, Somatic Symptom Disorder–B Criterion; PHQ-15, Patient Health Questionnaire Somatic Symptom Scale–15; PHQ-9, Patient Health Questionnaire Depression Scale–9; GAD-7, Generalized Anxiety Disorder Scale–7. All tests were significant after applying a Bonferroni adjustment for multiple testing. View Large Differential validity The comparison of the average SSD-12 scores from different patient groups (with and without chronic disease, with and without an indication of at least one psychological disorder and with and without indication of somatization) showed that the patients who suffer from a chronic disease (i.e. diabetes or hypertension) reported significantly higher SSD-12 scores than the patients without self-reported chronic disease. The same is true for patients with an indication of at least one psychological disorder or, more specifically, with somatization. Whereas the effect size measuring the differences in SSD-12 scores for patients with and without a chronic disease is rather small (d = 0.44), the differences in SSD-12 scores for patients with and without psychological disorders resulted in large effect sizes (d = 1.29 and 1.35, respectively). The comparison of the average SSD-12 scores from the different patient groups and the corresponding effect sizes are shown in Figure 2. Figure 2. View largeDownload slide Average SSD-12 sum-scores in different patient sub-groups from general practice. Figure 2. View largeDownload slide Average SSD-12 sum-scores in different patient sub-groups from general practice. Discussion The main aim of this study was to assess the usefulness and validity of the SSD-12 to measure the psychological characteristics of SSD in primary care. While there is already some evidence that supports the validity of the scale in specialized care and in the general population (11,12), it had not been applied to a primary care setting. Primary care practitioners represent an integral part of mental health care. As the patients’ usual first point of contact within the health care system, they not only connect patients to secondary and specialist services, but also have the unique opportunity to comprehensively evaluate the patients’ health and psychosocial context (16). The changes to the DSM-5 (and expected ICD-11) diagnostic criteria create a great opportunity to address the problem of under-diagnosis of somatoform disorders in the past. By emphasizing the psychological aspects associated with persistent somatic symptoms, it is possible that the new criteria may be more widely applied. This is especially likely as the diagnosis no longer relies on the idea that symptoms are ‘medically unexplained’. Previously, such uncertainty as to the cause of the symptoms often created unease in physicians who must balance the necessity of ruling out serious illness and increasing chronicity against the cost and distress of extensive testing (17). Primary care practitioners have the competing demands to treat and manage all or most of the patient’s acute and chronic conditions as well as providing preventive health care (17). Such competing demands create particular challenges for which the implementation of screening methods for mental disorders might be useful. This is particularly true as screening methods are time efficient and can open a discussion regarding the patient’s mental health. Since the vast majority of individuals with mental disorders never present to a mental health professional, mental health care is often undertaken at primary care (18). Therefore, there is a growing impetus to incorporate patient-reported outcome measures of symptoms and psychological distress into clinical practice (9). The SSD-12 could be a useful tool to assess psychological burden associated with bothersome somatic symptoms in primary care. Completion of the scale takes approximately 2–3 minutes, and the scoring is easily done within another minute. Its items are easy to understand and it measures a clear construct that patients feel is important to them (11). In the current study, the scale showed a high internal consistency and good item characteristics, apart from one item which showed somewhat problematic parameters. The disproportion of thoughts about the seriousness of one’s symptoms is very difficult for patients to judge themselves, but also for clinicians, especially since SSD can now also be accompanied by known diagnoses of somatic illness. Item 10 was explicitly included to reflect the opinions of physicians. This is in line with the Structured Clinical Interview for DSM-5 (SCID-5) (19), but its inclusion is at the expense of a higher heterogeneity of the scale. Confirmatory factor analyses performed on a ‘three latent dimensions’ model and on a ‘general-factor’ model both fit the data in an acceptable way. The calculation of three sub-scores is more in line with the structure of the DSM-5 criteria and this model might, therefore, be of greater importance for clinical purposes. However, since the three sub-criteria were demonstrably highly correlated in the current sample (Figure 1), a one-factor model suggestive of an overarching psychological burden factor should be favoured. This is in line with previous results from the general population (12). The high correlations between the three sub-criteria should further be discussed in the future. At this stage, it remains unclear whether these three DSM-5 suggested psychological aspects are the most valid, sensitive, and specific empirically founded features in patients with SSD (20). Accordingly, the SSD-12 total sum-score was used for the subsequent validation analyses: increases in total item scores represent increases in the general psychological burden associated with the somatic symptoms. The analysis revealed strong evidence of statistical associations with other measures. Since the psychological dimensions should, by definition, be highly associated with somatic symptom burden, bivariate correlations of SSD-12 and PHQ-15 sum-scores were conducted. The substantial association between the scales (r = 0.48) suggests that patients with a higher physical symptom load tend to report higher psychological burden. The correlations with GAD-7 and PHQ-9 were r = 0.54 and r = 0.60, respectively. These findings are plausible considering the high co-morbidity and partial overlap of somatoform, anxiety and depressive symptoms (21). This overlap is sometimes referred to as the somatization-anxiety-depression-triad, meaning that most patients experience combinations of these symptoms. It is fair to assume that the psychological burden associated with bothersome somatic symptoms is highly intertwined with anxiety and depressive symptoms. Nevertheless, studies show that these symptoms have independent, additive and differential effects on multiple domains of health-related quality of life, functional status, disability and health care use which, therefore, gives support to the differentiation of the three symptom domains (21). Patients who suffer from a chronic disease (i.e. diabetes or hypertension) reported significantly higher SSD-12 scores than patients without self-reported chronic diseases. The same is true for patients with an indication of at least one psychological disorder and, more specifically, somatization. They reported a higher level of psychological distress experienced through their somatic symptoms which means that at group level, the SSD-12 was found to be appropriate to differentiate between the respective patient groups. In contrast to the DSM-5 proposal of SSD, which sums up very heterogeneous patient groups, these results may indicate the importance to calculate separate norms for different patient groups (e.g. patients with or without accompanying serious physical disease, with mono- or poly-symptomatic disorder, with pain or illness anxiety disorder in particular). However, these results are to be considered in the context of patients’ self-reported data which is also one of the few limitations of the study: The diagnostic process did not include a ‘gold-standard’ diagnostic interview or another clinical evaluation to confirm the presence of psychiatric or somatic chronic disorders. Another limitation is that, so far, the SSD-12 does not provide a complete assessment of all DSM-5 criteria for SSD: it only covers the psychological B criteria. Criterion A can be assessed by using the PHQ-15 as a measure of somatic symptom severity, but DSM-5 also requires a ‘chronicity’ criterion (C) and allows the coding of specifiers like the presence of predominant pain, a persistent course with severe symptoms or marked impairment (1). In the future, the combined usage of the PHQ-15 and SSD-12 should be evaluated to ensure their applicability as screening instruments for somatic symptom disorder in primary care. For this purpose, longitudinal data on the SSD-12 is also needed to determine the scale’s test–retest reliability, its responsiveness to treatment and its minimum clinically important difference. So far, the current results indicate that administration of the SSD-12 immediately prior to a primary care consultation could be useful to facilitate patient-centred communication and shared decision making. While patients and providers may, for example disagree on the value of focusing on symptom severity as the main or only goal of treatment, they may be able to align on the common goal of reducing how much the symptoms are dominating a patient’s life which may also serve as a potential direct leverage point for psychological treatment. We believe that the SSD-12 will in the future be helpful in evaluating and monitoring patients’ psychological burden associated with persistent somatic symptoms and in the screening process for somatic symptom and related disorders, so that an earlier detection as well as more effective and quality of life-related interventions can be offered to patients suffering from persistent somatic symptoms. Supplementary material Supplementary data are available at Family Practice online. Declaration Funding: none. Ethical approval: the ethics board of the Medical Faculty of the Technical University of Munich (335/15). Conflicts of interest: none. Acknowledgements We would like to thank the patients, practitioners and staff from the primary care practices who gave their time to take part in this study. The data used for the analyses presented were collected for the MD thesis of Simon Kehrer at the Medical Faculty of the Technical University of Munich. References 1. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders (DSM-5) , 5th edn. Arlington, VA: American Psychiatric Association, 2013. 2. Dimsdale JE, Creed F, Escobar Jet al.   Somatic symptom disorder: an important change in DSM. J Psychosom Res  2013; 75: 223– 8. Google Scholar CrossRef Search ADS PubMed  3. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) . 4th edn, text revision. Washington, DC: American Psychiatric Association, 2000. 4. World Health Organization. The ICD-10 Classification of Mental and Behavioural Disorders: Clinical Descriptions and Diagnostic Guidelines . 10th edn. Geneva: World Health Organization, 1992. 5. Gureje O, Reed GM. Bodily distress disorder in ICD-11: problems and prospects. World Psychiatry  2016; 15: 291– 2. Google Scholar CrossRef Search ADS PubMed  6. Kurlansik SL, Maffei MS. Somatic symptom disorder. Am Fam Physician  2016; 93: 49– 54. Google Scholar PubMed  7. Hatcher S, Arroll B. Assessment and management of medically unexplained symptoms. BMJ  2008; 336: 1124– 8. Google Scholar CrossRef Search ADS PubMed  8. Jacobi F, Wittchen H-U, Holting Cet al.   Prevalence, co-morbidity and correlates of mental disorders in the general population: results from the German Health Interview and Examination Survey (GHS). Psychol Med  2004; 34: 597– 611. Google Scholar CrossRef Search ADS PubMed  9. Black N. Patient reported outcome measures could help transform healthcare. BMJ  2013; 346: f167. Google Scholar CrossRef Search ADS PubMed  10. Kroenke K, Spitzer RL, Williams JB. The PHQ-15: validity of a new measure for evaluating the severity of somatic symptoms. Psychosom Med  2002; 64: 258– 66. Google Scholar CrossRef Search ADS PubMed  11. Toussaint A, Murray AM, Voigt Ket al.   Development and validation of the Somatic Symptom Disorder–B Criteria Scale (SSD-12). Psychosom Med  2016; 78: 5– 12. Google Scholar CrossRef Search ADS PubMed  12. Toussaint A, Löwe B, Brähler E, Jordan P. The Somatic Symptom Disorder–B Criteria Scale (SSD-12): factorial structure, validity and population-based norms. J Psychosom Res  2017; 97: 9– 17. Google Scholar CrossRef Search ADS PubMed  13. Kroenke K, Spitzer RL, Williams JB. The PHQ-9: validity of a brief depression severity measure. J Gen Intern Med  2001; 16: 606– 13. Google Scholar CrossRef Search ADS PubMed  14. Löwe B, Decker O, Müller Set al.   Validation and standardization of the Generalized Anxiety Disorder Screener (GAD-7) in the general population. Med Care  2008; 46: 266– 74. Google Scholar CrossRef Search ADS PubMed  15. Schreiber JB, Nora A, Stage FK, Barlow EA, King J. Reporting structural equation modeling and confirmatory factor analysis results: a review. J Educ Res  2006; 99: 323– 37. Google Scholar CrossRef Search ADS   16. Starfield B. Is primary care essential? Lancet  1994; 344: 1129– 33. Google Scholar CrossRef Search ADS PubMed  17. Murray AM, Toussaint A, Althaus A, Löwe B. The challenge of diagnosing non-specific, functional, and somatoform disorders: a systematic review of barriers to diagnosis in primary care. J Psychosom Res  2016; 80: 1– 10. Google Scholar CrossRef Search ADS PubMed  18. Rief W, Martin A, Klaiberg A, Brähler E. Specific effects of depression, panic, and somatic symptoms on illness behavior. Psychosom Med  2005; 67: 596– 601. Google Scholar CrossRef Search ADS PubMed  19. First MB, Williams JBW, Karg RS, Spitzer RL. Structured Clinical Interview for DSM-5—Research Version (SCID-5 for DSM-5, Research Version; SCID-5-RV) . Arlington, VA: American Psychiatric Association, 2015. 20. Rief W, Martin A. How to use the new DSM-5 somatic symptom disorder diagnosis in research and practice: a critical evaluation and a proposal for modifications. Annu Rev Clin Psychol  2014; 10: 339– 67. Google Scholar CrossRef Search ADS PubMed  21. Kohlmann S, Gierk B, Hilbert A, Brähler E, Löwe B. The overlap of somatic, anxious and depressive syndromes. J Psychosom Res  2016; 90: 51– 6. Google Scholar CrossRef Search ADS PubMed  © The Author(s) 2017. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

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Family PracticeOxford University Press

Published: Nov 13, 2017

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