Independent validation of the scales for outcomes in Parkinson's disease-autonomic (SCOPA-AUT)

Background and purpose. Autonomic dysfunction is common in Parkinson's disease (PD) and causes a great impact in health-related quality of life (HRQL) and functional status of patients. This study is the first independent validation of the Scales for Outcomes in PD-Autonomic (SCOPA-AUT). Methods. In an observational, cross-sectional study (ELEP Study), 387 PD patients were assessed using, in addition to the SCOPA-AUT, the Hoehn and Yahr staging, SCOPA-Motor, SCOPA-Cognition, Cumulative Illness Rating Scale-Geriatrics, modified Parkinson Psychosis Rating Scale, Clinical Impression of Severity Index for PD, Hospital Anxiety and Depression Scale, SCOPA-Sleep, SCOPA-Psychosocial, pain and fatigue visual analogue scales, and EQ-5D. SCOPA-AUT acceptability, internal consistency, construct validity, and precision were explored. Results. Data quality was satisfactory (97%). SCOPA-AUT total score did not show floor or ceiling effect, and skewness was 0.40. Cronbach's alpha coefficients ranged from 0.64 (Cardiovascular and Thermorregulatory subscales) to 0.95 (Sexual dysfunction, women). Item homogeneity index was low (0.24) for Gastrointestinal subscale. Factor analysis identified eight factors for men (68% of the variance) and seven factors for women (65% of the variance). SCOPA-AUT correlated at a high level with specific HRQL and functional measures (r(S) = 0.52-0.56). SCOPA-AUT scores were higher for older patients, for more advanced disease, and for patients treated only with levodopa (Kruskal-Wallis test, P < 0.01). Standard error of measurement for SCOPA-AUT subscales was 0.81 (sexual, men) - 2.26 (gastrointestinal). Conclusions. Despite its heterogeneous content, which determines some weaknesses in the psychometric attributes of its subscales, SCOPA-AUT is an acceptable, consistent, valid and precise scale.