Multiple System Atrophy Combined Outcome Assessment (MuSyCA): process, format, and validation plan

The Unified Multiple System Atrophy Rating Scale (UMSARS) is widely used as an outcome measure in MSA trials, but it has limitations for clinical trial use. To address these, we developed the Multiple System Atrophy Combined Outcome Assessment (MuSyCA), a comprehensive multimodal tool for disease-modifying MSA trials. The purpose of this manuscript is to describe the development and validation plan for MuSyCA, with emphasis on its structure, intended use, and assessment of reliability, validity, and sensitivity in tracking disease progression.

The development of MuSyCA followed a multistep process. Candidate outcome assessments were identified through systematic literature review and analysis of longitudinal data from large MSA cohorts. Content was refined through multiple Delphi-like consensus rounds involving MSA experts, patient advocacy groups representatives, and industry stakeholders. Cognitive interviews conducted in 20  patients with MSA evaluated the clarity and clinical relevance of patient- and clinician-reported outcomes; feedback was incorporated into a subsequent version of the MuSyCA. Validation is ongoing and includes assessment of construct validity, internal consistency, test-retest reliability, and responsiveness. Longitudinal analyses to determine sensitivity to change over time are ongoing.

MuSyCA combines patient- and clinician-reported outcomes, biomarkers (neurofilament light chain, neuroimaging), and performance-based measures to capture subjective and objective aspects of MSA progression, enhancing its utility  to detect treatment effects in clinical trials. MuSyCa is not intended to be used in clinical practice.

MuSyCA offers a multidimensional approach to MSA assessment, supporting precise, disease-relevant evaluations in trials of putative disease-modifying therapies. Its validation will provide a standardized multimodal outcome measure, advancing MSA therapeutic development.