Correlations between clinical motor scores and CMAP in patients with type 2 spinal muscular amyotrophy treated with nusinersen

Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by the degeneration of the anterior horn cells of the spinal cord. Nusinersen for the treatment of SMA has been covered by public healthcare in France since May 2017. Our aim was to investigate whether there is a correlation between clinical and compound motor action potential (CMAP) measurements in SMA patients treated with nusinersen after 3 years’ follow-up. Motor skills were evaluated regularly between M0 and M36 using the Motor Function Measure (MFM) score. CMAP measurements were collected regularly between M0 and M22. Data for 10 patients with SMA type 2 were collected and divided into two age groups (< 5 years and > 5 years). Motor function improved, but not significantly, regarding distal motor skills (D3) in both groups, and in axial and proximal motor function (D2) in the younger group. CMAP measurements improved in all patients. CMAP increased significantly for the median nerve, and this improvement correlated significantly with global MFM and with axial and proximal tone (D2). Our study shows gain in distal motor function with nusinersen, especially in younger patients with SMA type 2. These results encourage the screening of SMA patients and treatment as early as possible. CMAP measurements of the median nerve show clear improvement in patients treated with nusinersen and could be performed as routine follow-up.