F-wave latencies of the deep peroneal nerve in diabetic polyneuropathy.

The F-wave latency of the deep peroneal nerve in function of leg length was determined in 66 normal persons and 25 diabetic patients with known polyneuropathy. The latencies were measured by stimulating the nerve at the ankle and recording the F-wave at the musculus extensor digitorum brevis using a needle electrode. The leg length was represented by the distance between the spina iliaca anterior superior and the lateral malleolus. The F-wave latencies obtained in diabetic patients were significantly higher than in controls (p less than 0.01). The method is suitable to detect polyneuropathy, especially in early cases where the conventional techniques (determination of the motor and/or sensory latencies and/or conduction velocities at the lower limbs) may still yield normal or borderline values. The upper limits of the normal values of the F-wave latencies in function of leg length is given by a non-linear curve, which can be represented by the equation: F-wave latency (msec) = 14.7 + 47.5 x (leg length in m)2. For practical purposes, the upper limit of the normal value for a given leg length can be readily determined from a latency-length curve.