Distal slowing of motor nerve conduction velocity in diabetic polyneuropathy.

Using the latencies of M response and F wave, motor nerve conduction was assessed along the entire course of the nerve from the spinal cord to the muscle in 102 diabetics and 74 control patients. In diabetics, latencies were increased and conduction velocity decreased over both proximal and distal segments. However, the latency ratio of the proximal to distal segment (F ratio) was slightly but significantly smaller in diabetics (mean +/- SD:0.93 +/- 0.14, 1.35 +/- 0.20, 1.09 +/- 0.19 and 1.02 +/- 0.19 for median, ulnar, tibial and peroneal nerves, respectively) than in control patients (1.05 +/- 0.09, 1.41 +/- 0.12, 1.17 +/- 0.13 and 1.08 +/- 0.12). These findings suggest that motor conduction abnormalities in diabetic polyneuropathy are diffuse over the total length of the nerve, but more intense in the distal than proximal segment. An additional finding in diabetics was that both proximal and distal segments were more frequently affected in the lower than in the upper extremities.