F-wave conduction velocity in the deep peroneal nerve: Charcot-Marie-Tooth disease and dystrophia myotonica.

The F-wave has been used to estimate the motor nerve conduction velocity (MNCV) along the proximal segment (spinal cord to knee) of the axons of the deep peroneal nerve in patients with Charcot-Marie-Tooth disease and those with dystrophia myotonica. A new, modified method has been applied to estimate proximal MNCV in patients in whom F-waves or M-responses cannot be obtained from the small muscles of the foot. Terminal latencies and MNCV along the distal nerve segment (knee to ankle) have also been estimated using conventional techniques. The results have been compared with those obtained for control subjects. Proximal MNCV was severely slowed in every patient with Charcot-Marie-Tooth disease; the degrees of proximal and distal MNCV decreases were related. In patients with dystrophia myotonica, distal and proximal MNCVs were significantly reduced in comparison with control subjects, the MNCV slowing was not related to the degree of muscle atrophy. This is consistent with the hypothesis that the nerves and muscles are independently affected in dystrophia myotonica. It is concluded that the F-wave MNCV technique is as useful as, and may be more sensitive than, the conventional MNCV method.