Diagnostic value of electromyogram in congenital spinal muscular atrophy of the neonate

Background.- The acute form of Werdnig-Hoffman disease, infantile spinal muscular atrophy type I (SMA I), is characterized by severe paralytic hypotonia with neurogenic electromyographic (EMG) pattern and specific histologic features. Patients.- Four cases of very severe SMA I suffering from general ized muscle weakness at birth were included in the study. Results.- The neurogenic EMG pattern war observed at the first exam performed between D2 and D46. The muscular biopsy performed between D18 and D45 showed only a mild decrease of the muscle fiber size without grouping of fiber types. Conclusion.- In those forms of SMA I with a neonatal clinical onset, the diagnosis is assessed by clinical and EMG findings while early muscular biopsy can be misleading. EMG is the relevant diagnostic test which confirms the anterior horn cell disease and can justify the DNA study.