The Spinal Muscular Atrophy Functional Classification System

AIM: To develop a functional mobility classification for spinal muscular atrophy (SMA), reflecting changing phenotypes in the era of disease-modifying agents, with associations to hip displacement, scoliosis, and pulmonary function determined. METHOD: Patients with SMA and Hammersmith Functional Motor Scale Expanded (HFMSE) assessments were included. The Spinal Muscular Atrophy Functional Classification System (SMAFCS), comprising levels I to IV, was constructed, referencing Functional Mobility Scale groupings. Receiver-operating characteristic analysis determined HFMSE thresholds by SMAFCS. Associations of hip displacement, scoliosis, and pulmonary function were determined. RESULTS: Sixty patients (62% female) were included, with 312 HFMSE assessments (mean 5.3 [SD 2.7] per patient) over 7 years 6 months (SD 3 years 11 months). HFMSE thresholds by SMAFCS level were I, ≥27; II, ≥22,