Respiratory effects of nusinersen treatment in pediatric patients with spinal muscular atrophy types 2 and 3

Introduction : Spinal muscular atrophy (SMA) is a progressive neuromuscular disorder characterized by respiratory decline. While nusinersen improves motor function, its long-term respiratory effects in milder SMA types (2 and 3) remain unclear. This study evaluates pulmonary outcomes following 3 years of treatment. Methods : We retrospectively reviewed genetically confirmed SMA 2 and 3 pediatric patients treated with nusinersen (2017-2022). Data included demographics, non-invasive ventilation (NIV) and mechanical insufflation-exsufflation (MIE) use, body mass index (BMI), feeding method, scoliosis, and respiratory hospitalizations. Pulmonary function tests (PFTs) at baseline and at year 3 included percent-predicted forced vital capacity (ppFVC), FEV1/FVC ratio, peak cough flow (PCF), maximal voluntary ventilation (MVV), maximal inspiratory pressure (MIP), and maximal expiratory pressure (MEP). Results : Included were 15 patients with type 2 and 13 patients with type 3 SMA. Their mean age at diagnosis was 3.5 ± 4 years and 13.8 ± 5.4 years at nusinersen initiation. One was lost to follow-up. At baseline, 6 patients used NIV and 8 used MIE. After 3 years, NIV use increased to 7/27 and MIE to 14/27. All 27 patients maintained oral intake and their BMI remained stable. ppFVC declined, most notably in year 3 (−13.5%, p <0.001). PCF, MVV, MIP, and MEP values remained stable or mildly improved, suggesting a slower decline or relative stabilization compared to natural progression. Conclusions : Nusinersen may help preserve respiratory muscle strength and delay ventilatory support requirement among pediatric patients with SMA types 2 and 3. Although ppFVC declined, stability in other parameters supports a potential respiratory benefit.