Reliability, Validity and Determinants of Self-Reported Autonomic Dysfunction in Prodromal and Established Parkinson's Disease.

BACKGROUND: Scales for Outcomes in Parkinson's Disease Autonomic Dysfunction Scale (SCOPA-AUT) is a widely used, self-reported scale to evaluate autonomic dysfunction in PD. Recent literature on interoception has raised questions about validity. Several knowledge gaps remain minimal detectable change (MDC), best subscale structure, validation against objective autonomic measures, and performance in prodromal populations. OBJECTIVE: To critically expand knowledge of SCOPA-AUT's measurement properties with novel analyses to increase confidence as an outcome measure. METHODS: Data from the Parkinson's Progression Markers Initiative (PPMI) were analyzed. Exploratory and confirmatory factor analyses determined subscale structure. Test-retest reliability helped derive the MDC. Criterion and construct validity were assessed using objective measures (e.g., orthostatic hypotension (OH)) with area-under-the-curves and correlations. Mixed models identified the best predictors of self-reported autonomic dysfunction. RESULTS: Data on 4450 individuals, including healthy controls (n = 343), prodromal (n = 2539) and established PD (n = 1503) participants, were analyzed. The total scale had strong reliability (ω = 0.86; ICC = 0.78), with an MDC≥6. The published six-subscale structure showed adequate fit, but splitting the gastrointestinal domain into upper (oral) and lower (intestinal) factors significantly improved model fit. Criterion validity against objective OH was poor (AUC = 0.59). SCOPA-AUT correlated most strongly with non-motor experiences of daily living (rs = 0.62, large effect), which was also its strongest longitudinal predictor, followed by motor experiences of daily living. CONCLUSIONS: SCOPA-AUT is a reliable, valid scale in prodromal and established PD. The published subscale, while adequate, may benefit from modification. SCOPA-AUT correlates robustly with non-motor, followed by motor experiences of daily living, supporting its continued use.