Objective: To evaluate the psychometric properties, reliability, and validity of a modified version of UMSARS Part I (mUMSARS), collapsing response categories 0 and 1 and removing item 11 [sexual function].

Background: The UMSARS is currently regarded as the most widely accepted clinical outcome measure in MSA. However, as with many rating scales, it has recognized limitations, which are particularly relevant in the context of a rare disease. Scale modifications have been recommended to improve sensitivity and clinical relevance for registrational studies. The increasing number of modified UMSARS versions underscores the need for psychometric evaluation to support their use as trial endpoints.

Method: The AMULET study (NCT05104476) was a randomized, double‑blind, placebo‑controlled, multicenter 48–72‑week trial evaluating amlenetug versus placebo in adults aged 40–75 years with possible or probable MSA, motor symptom onset within 5 years, and a UMSARS Part I score ≤16 (excluding item 11). Clinician‑rated assessments included the UMSARS (Parts I and II video‑recorded for central review) and Clinical/Patient/Observer Global Impressions of Severity (CGI‑S/PGI‑S/OGI‑S). The primary endpoint was UMSARS total score (Part I + 2) progression, with mUMSARS as a key secondary endpoint. Descriptive statistics, internal consistency (Cronbach’s alpha), test–retest reliability (ICCs), and construct and criterion validity (polychoric and Spearman correlations with related clinical measures) were evaluated.

Results: As expected, mUMSARS scores shifted to higher response categories over time with disease progression. The modified scale demonstrated acceptable internal consistency and good test–retest reliability (Cronbach’s alpha 0.80 at Week 48 and 0.76 at end of treatment [EOT]; longitudinal ICC [EOT] 0.60). Construct validity was stronger than UMSARS Part I and comparable to the UMSARS total score. The mUMSARS showed moderate Spearman correlations at baseline with UMSARS Part IV, CGI‑S, and PGI‑S (r = 0.51–0.64) and a strong correlation with OGI‑S (r = 0.72).

Conclusion: The mUMSARS demonstrates acceptable psychometric performance and greater responsiveness than UMSARS Part I, supporting its use as a sensitive, fit for purpose primary endpoint in the target MSA population.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/psychometric-assessment-of-a-modified-version-of-the-unified-multiple-system-atrophy-rating-scale-part-i/