Course of joint range of motion in children with spinal muscular atrophy receiving disease-modifying treatment

BackgroundProgressive decreases in joint range of motion (ROM) is a well-recognized complication in the natural history of spinal muscular atrophy (SMA). How joint ROM evolves in children with SMA receiving disease-modifying treatment (DMT) needs to be documented.PurposeTo examine the longitudinal course of joint range of motion in young children with SMA receiving disease-modifying therapy.MethodsWe included children with SMA (with 2 or 3 SMN2 copies) who started treatment within the first 18 months of life in a prospective national tertiary cohort study. Our examination consisted of joint range of motion of the knee, elbow and wrist; the longitudinal course was studied using linear mixed-effects models.ResultsWe analysed 165 visits of 39 children (median age 22 months (interquartile range [6–45])) with treated SMA over a 3-year follow-up period. The median age at start of treatment was 2 months [0–8]. We found an average yearly decline in knee extension mobility of 3°. The overall course of range of motion for elbow and wrist remained stable.ConclusionThe course of joint mobility in children with SMA, who started treatment with DMT in the first 18 months of life, is characterised by a decline in knee extension and a stable range of motion of wrist and elbow joints. We stress the importance of monitoring knee extension range of motion at least every 6 months and adopting a proactive approach to maintain full knee extension for optimal lifelong mobility.