Pulmonary function and scoliosis in children with spinal muscular atrophy types II and III

Aims: The objectives were to evaluate the clinical course of spinal muscular atrophy (SMA) types II and III patients necessitating scoliosis surgery at the National University Hospital, Singapore. Methods: A retrospective review of SMA types II and III patients, born over a 10-year period between 1983 and 1992, was conducted. Results: There were eight patients: four with SMA type II and four with SMA type III. The mean age at scoliosis surgery was 9 years 7 months (range 7 years 6 months–12 years 4 months). The mean preoperative Cobb angle was 65.4 ° (range 43–90 ° ) and the mean postoperative Cobb angle was 22.6 ° (range 12–45 ° ), with a mean correction of 64.8% (range 47.7–77.8%). The decline in percentage predicted forced vital capacity (FVC) was 7.7% (95% CI: 12.4% to 3.0%) per year preoperatively and this was reduced to 3.8% (95% CI: 5.8% to 1.9%) per year postoperatively. The mean length of preoperative and postoperative lung function follow-up was 6.3 months (range 0.03–31 months) and 44 months (range 0–110 months), respectively. Conclusions: This study suggests that pulmonary function in SMA types II and III continues to decline after scoliosis surgery, though the rate of decline is less marked. Overall, the combined results from this study and all other previously published studies are conflicting in regard to the effect of scoliosis surgery on pulmonary function in SMA types II and IIII, though half of the studies (3 of 6) did demonstrate a continued decline in lung function postoperatively. This decline in pulmonary function despite spinal stabilization is likely secondary to the progressive neuromuscular weakness of the disease. Spinal muscular atrophy (SMA) is a rare neuromuscular disorder causing degeneration of anterior horn cells of the spinal cord, resulting in symmetrical muscle weakness. Three forms of SMA have been identified. SMA type I is the most severe form of the disease with its onset before 6 months of age, and often in utero . Infants with this form of the disease are ‘floppy’ at birth or develop floppiness over time. They are never able to sit unsupported, and death usually occurs before 2 years of age. SMA type II is an intermediate form of the disease, with its onset between 6 months and 18 months of age. Children with this intermediate form are able to sit unsupported, but they are unable to stand or walk unaided. Patients die of respiratory failure above the age of 2 years, secondary to muscle weakness and progressive scoliosis. However, many of these patients will not die until early adulthood. SMA type III is a mild form of the disease, with its onset after 18 months of age. Patients can stand independently and walk unaided. The rate of progression of muscle weakness is slower and death usually occurs in adulthood. 1,2 Patients with SMA tend to develop spinal deformities, with scoliosis being the most severe problem in surviving patients. 3 Scoliosis impairs lung function by reducing the mechanical efficiency of the chest wall. The effect of scoliosis surgery on pulmonary function in these patients has not been well described. There have been several previously published studies on this subject, but as SMA type II and type III are relatively rare diseases, all of the studies (including this study) were relatively small case series. The objectives of this study were to evaluate and describe the clinical course of SMA types II and III, as well as to determine the effect of scoliosis surgery on pulmonary function.