Test-retest reliability and associations of strength and functional outcome measures in adults with spinal muscular atrophy

Abstract

Disease-modifying therapies for spinal muscular atrophy (SMA) require standardized follow-up to interpret treatment response. However, short-term changes may reflect measurement variability rather than true clinical change. We therefore assessed the test-retest reliability and relationships of routinely used outcome measures in adults with SMA using two standardized evaluations performed within a two-week interval. These assessments included motor function, upper-limb strength and dexterity, ambulatory performance, and respiratory function. Forty-four adults with SMA type 2 or 3 were included. No significant change was observed between test and retest visits. Most outcomes demonstrated excellent reproducibility, with intraclass correlation coefficients (ICC) >0.95. Measurement errors were low, with relative standard errors of measurement below 10% for most outcomes. Strong correlations were observed among most outcomes ( p  < 0.001). Commonly used functional measures in adults with SMA show high short-term reliability. Based on reliability, measurement error, and inter-test correlations, grip strength, MFM, RULM, and FVC appear to be among the most reliable measures, although RULM may be limited by known ceiling and floor effects.