A changing early onset scoliosis phenotype in spinal muscular atrophy: nusinersen treatment is associated with younger age, increased curve magnitude, and kyphosis at the time of index surgery

BACKGROUND: Nusinersen provides functional benefits to Spinal Muscular Atrophy (SMA) patients but does not affect the prevalence or progression of scoliosis. This study aims to characterize perioperative curve characteristics and patient demographics among patients with SMA undergoing surgical treatment for early onset scoliosis (EOS) in a period spanning the introduction of nusinersen, a disease-modifying therapy. METHODS: This retrospective cohort study utilized a multicenter international pediatric spinal deformity database. Patients with SMA undergoing initial surgical treatment for scoliosis between 1996 and 2023 were included. Patients were stratified by exposure to nusinersen preoperatively. Preoperative clinical, radiographic characteristics, and first erect postoperative radiographic parameters were compared between groups. RESULTS: A total of 210 patients were included, 37 with preoperative nusinersen exposure and 173 controls. Patients in the nusinersen group were younger at the time of intervention (6.5 vs. 7.6 years, p = 0.006) and had more spinal levels instrumented post-operatively (10.5 vs. 9.5, p = 0.033). Preoperative kyphosis (78° vs. 67°, p = 0.027) and major curve magnitude (83° vs. 75°, p = 0.030) were higher in the nusinersen group. Postoperative kyphosis was also greater in this group (48° vs 42°, p = 0.042). There was no difference in postoperative major curve magnitude or percent correction. The nusinersen group was more commonly treated with magnetically controlled growing rods. A contemporaneous subgroup analysis (post-2017) showed that patients treated with nusinersen were younger at the time of surgery, although no significant differences in preoperative curve characteristics were noted. CONCLUSION: Nusinersen exposure was associated with younger age at surgery, greater curve magnitude, and increased kyphosis. These findings highlight potential changes in the phenotype of surgical candidates with EOS and SMA among patients treated with Nusinersen.