Long term follow-up of scoliosis progression in type II SMA patients

: The aim of this study is to retrospectively assess onset and progression of scoliosis in type II SMA patients not treated with the approved disease modifying treatments. Scoliosis was evaluated by measuring the scoliosis angle on X-ray obtained in the anteroposterior view in sitting position (Cobb's angle method). Eighty-four patients had at least one assessment of scoliosis angle (287 assessments). There was a positive correlation between age and scoliosis angles (p<0.001) with a progressive increase of scoliosis with age. When subdividing the population by HFMSE score (<10; 11-22;> 22), there was a progressive increase in scoliosis angles with decreasing HFMSE scores. The difference between HFMSE categories was significant (p<0.001). Fifty-four patients had at least two assessments at 6-month distance and were retained for the longitudinal analysis. Using a mixed model, age, functional status and scoliosis angle at baseline were predictive on scoliosis progression. The mean annual rate of increase of scoliosis angle was 5.63 (95%CI: 4.74-6.52). Our results confirm the progression of scoliosis in untreated type II SMA providing details of the progression in relation to different variables. With different therapeutical options being available in many countries, our findings will provide reference data for establishing possible differences in the trajectories of progression with treated type II individuals.