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

BACKGROUND: Progressive 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.

PURPOSE: To examine the longitudinal course of joint range of motion in young children with SMA receiving disease-modifying therapy.

METHODS: We 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.

RESULTS: We 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.

CONCLUSION: The 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.