Italian validation of the SMA independence scale-upper limb module.

Abstract

Spinal muscular atrophy (SMA) is a progressive disorder caused by SMN1 mutations. While therapies have changed its course, current motor scales often miss aspects. This study aimed to validate the Italian SMA Independence Scale (SMAIS-ULM) for reliability, applicability, and expansion across diverse SMA phenotypes. Patients with genetically confirmed 5qSMA were recruited from 12 Italian centers. Analyses included Intraclass Correlation Coefficients (ICCs) for test-retest reliability, the Kruskal-Wallis for group comparisons, and the Spearman correlations with functional measures. Ceiling/floor effects were defined as ≥ 85% of a group reaching the maximum or minimum score. The study analyzed 472 completed questionnaires: 263 from caregivers (mean age 26.4 ± 17.6; 29 SMA I, 123 SMA II, 104 SMA III, 7 presymptomatic) and 209 from patients (mean age 33.1 ± 16.4; 3 SMA I, 101 SMA II, 104 SMA III; 1 SMA IV), including 195 matched caregiver-patient pairs. ICC was conducted in 29 caregivers and 31 patients; values ranged from 0.97 to 1.00. SMAIS-ULM scores differed by SMA type, with SMA III/presymptomatic subjects scoring higher than SMA I/II (p < 0.001) and walkers scoring higher than sitters/non-sitters (p < 0.001). Floor effects were found in 18.9% of non-sitters and 50% of walkers, with comparable patterns in patient responses. Strong correlations with functional measures were found, with no significant differences between caregiver and patient reports. Conclusion: The findings confirm the reliability and validity of the SMAIS-ULM as an effective tool for measuring functional independence in individuals with SMA, both from the caregiver and patient perspectives.