An Exploratory 12-Month Observational Study of Adults with Spinal Muscular Atrophy: Learning From Our Tools

To describe motor, respiratory and quality of life changes in a mixed cohort of adults with spinal muscular atrophy (SMA) from a single tertiary rehabilitation center in Canada and to report preliminary psychometric evidence of a nationally recommended core outcome set over 12 months.

This real-world, mixed-treatment cohort, exploratory, single-site, prospective observational study followed fifteen adults with SMA over 12 months. Participants completed the Spinal Muscular Atrophy Recommended Toolkit (SMART), which consists of eight outcome measures (OM) assessed at baseline and 12 months. Concurrent and predictive validity were assessed using Spearman's Correlation Coefficient (SCC). Longitudinal change and sensitivity to change were evaluated using the Wilcoxon signed-rank test and standardized response mean.

Ten participants were receiving disease-modifying treatments. None of the OMs demonstrated statistically significant changes over 12 months. Respiratory and motor function measures are independently clustered into two clusters. Only the Children's Hospital of Philadelphia - Adult Test of Neuromuscular Disorders (CHOP-ATEND) exhibited high sensitivity to change. Forced vital capacity (FVC) >2 L or peak cough flow (PCF) >200 L/min corresponds with ceiling effects of the Revised Upper Limb Module (RULM) and SMA Functional Rating Scale (SMAFRS).

This exploratory study identified two collinear clusters between SMART OMs, suggesting measurement redundancy. SMART OMs did not demonstrate significant changes over 12 months in this small mixed-treatment cohort. Developing new OMs that are valid, reliable and responsive, and optimizing OM selection will reduce clinic and patient burden, and improve clinical utility in a real-world setting.