A Prospective Cohort Study on Quantitative Muscle Magnetic Resonance Imaging During the Treatment of Spinal Muscular Atrophy Types 2 and 3 in Children.

Background: Nusinersen has been promoted as an effective therapy for improving motor function in patients with spinal muscular atrophy (SMA). Quantitative magnetic resonance imaging (qMRI) is a useful tool to reflect muscle microstructural characteristics. We investigate whether qMRI can provide useful biomarkers for monitoring treatment efficacy in SMA and explore other factors that may predict the treatment response.

Methods: Pelvic and thigh qMRI (Dixon, T2 mapping, and diffusion-tensor imaging) and Hammersmith Functional Motor Scale Expanded (HFMSE) scores were evaluated at baseline and at six months after nusinersen treatment in 28 patients. X-ray examinations to obtain Cobb angle were performed at baseline. Minimally clinically important difference (MCID) was defined by a gain in HFMSE score of at least 3 points from the baseline.

Results: The HFMSE score correlated significantly with all of the qMRI parameters and the Cobb angle at baseline. After six months of treatment, the mean thigh fat fraction (FF) and fractional anisotropy decreased and the HFMSE increased, whereas T2 and the apparent diffusion coefficient remained stable. The HFMSE changes over six months were correlated negatively with baseline age, and MCID at six months after treatment was more likely in patients younger than 4.6 years. Moreover, changes in FF were significantly greater in patients with type 2 than in type 3 SMA.

Conclusions: qMRI has the potential to be used to evaluate the effect of nusinersen over time in patients with SMA. Younger age at the start of treatment may predict better improvements in motor function.