Characteristics of early-onset, rapidly progressive scoliosis in spinal muscular atrophy type I treated with disease-modifying therapy -a multicenter retrospective study conducted in Japan.

In the era of disease-modifying therapy (DMT), almost all patients with spinal muscular atrophy (SMA) type I treated after onset, but before 6 months of age, develop early-onset, rapidly progressive scoliosis by 2 years of age, despite improvements in their motor function. Seven symptomatic patients with SMA type I who were treated before the age of 6 months were included in this retrospective observational study. Scoliosis had developed in all patients by 27 months of age. Among them, the patients who could stand with support or independently (standing patients; n = 3) tended to present with more progressive scoliosis than the sitters (n = 4). All standing patients demonstrated thoracic hyperkyphosis before or at the time of their scoliosis diagnosis. Despite receiving DMT, these patients continued to show residual key manifestations of SMA type I. Chronic difficulty maintaining posture due to trunk muscle weakness in the lying, sitting, or standing position was considered to be the main contributor to the development and progression of the scoliosis. The development and progression of such scoliosis, which begins in infancy, may be related to inappropriate postural management, which is not currently recognized as such by clinicians, caregivers, or guardians. In this population, it is important to closely monitor patients for such scoliosis from soon after the diagnosis of SMA. As this type of scoliosis progresses rapidly during the early developmental stage, when surgery is not possible, it is necessary to establish a proactive non-surgical management strategy for it.