Reliability of the modified Hammersmith functional motor scale in young children with spinal muscular atrophy

Introduction: The test-retest reliability of the Modified Hammersmith Functional Motor Scale (MHFMS) in children with spinal muscular atrophy (SMA) ±30 months of age was assessed. The age at which typically developing children (TD) achieve maximum MHFMS scores was also studied. Methods: Twenty-two children with SMA type II [mean age (SD) = 20 (5) months, range 9-30 months) were tested twice using the MHFMS. Twenty-five TD children [mean age (SD) = 18 (7) months, range 9-30 months) were tested once. Results: The average difference between MHFMS scores for SMA children was 0.18 [first assessment: mean (SD) = 12.8 (9.8); second assessment: mean (SD) = 13.0 (8.8)]. Reliability was excellent (ICC_1,3 = 0.96, SEM 1.86). TD participants had MHFMS scores ranging from 36 to 40 [mean (SD) = 39.2 (1.2)] and achieved maximum test scores at 12 months of age. Discussion: MHFMS scores in young children with SMA type II showed excellent test-retest stability. This suggests that the MHFMS can be used reliably in this younger population for clinical trials and follow-up.