Clinical utility of dorsal sural nerve conduction studies

A technique of testing sensory nerve conduction of the dorsal sural nerve in the foot was used in 38 normal subjects and 70 patients with peripheral neuropathies. The normal dorsal sural sensory nerve action potential (SNAP) had a mean amplitude of 8.9 microV (range 5-15 microV), mean latency to negative peak of 4.0 ms (range 3.2-4.7 ms), and mean conduction velocity of 34.8 m/s (range 30-44 m/s). Optimal placement of the recording electrodes to obtain a maximal nerve action potential was proximal to digits 4 and 5. Cooling to below 25 degrees C prolonged the latency but did not decrease the SNAP amplitude. Among the patients with peripheral neuropathy, dorsal sural SNAP was absent in 68 (97%), whereas only 54 (77%) showed abnormalities of sural sensory conduction. The diagnostic sensitivity of sensory nerve conduction studies in peripheral neuropathies may be significantly improved by the use of this technique for evaluating the action potential of the dorsal sural nerve.