[Electromyographic study of 50 cases of Werdnig-Hoffmann disease].

An electromyographic study was performed in 50 cases of severe infantile spinal muscular atrophy (type I). 164 muscles and 93 nerves (ulnar and posterior tibialis) were tested. The thresholds of stimulation of the motor nerves were increased. Motor action potential was absent in 30% of the investigated nerves, motor nerve conduction velocity was slow in 44%, H reflex was absent in 86%. Proprioceptive nerve conduction velocity was slow in some cases. Using the long-time (50-100 msec) direct longitudinal technique of muscle stimulation (provoked fibrillation), denervation could be proved in 98% of cases. The authors emphasize diagnostical difficulties in the first days of life.