Sensory (1a) and F-wave conduction velocity in the proximal segment of the tibial nerve.

The F-wave was used to estimate the fastest motor nerve conduction velocity (MNCV) along the proximal segment (spinal cord to knee) of the axons of the tibial nerve in 65 control subjects, 8 patients with diabetic polyneuropathy, and 4 patients with Charcot-Marie-Tooth disease. Terminal latencies and MNCV along the distal segment (knee to ankle) of the nerve were also estimated with the conventional M-response technique. This article describes another method for estimating sensory nerve conduction velocity (SNCV) along 1a fibers of the tibial nerve for the spinal cord-to-knee segment. Proximal and distal MNCV showed moderate slowing in patients with diabetic polyneuropathy and severe slowing in those with Charcot-Marie-Tooth disease. In 17 control subjects, proximal MNCV for the axons supplying the abductor hallucis muscle was compared to that estimated for the axons to the gastrocnemius muscle. MNCV for the proximal is faster than that for the distal small muscle. In 2 patients, M- and F-responses were not obtained from the abductor hallucis; in these patients, effective estimation of the proximal MNCV was made from the gastrocnemius muscle and showed marked reduction.