Diabetic neuropathy: electrophysiologic abnormalities of distal lower extremity sensory nerves.

Electrophysiologic parameters of the medial dorsal cutaneous (MDC) and the sural nerves were analyzed in 119 diabetic patients with clinical signs and symptoms of neuropathy. Fifty-five patients were insulin dependent (ID), mean age 47.4, and 64 were non-insulin dependent (NID), mean age 55.2. Using age-adjusted criteria for the sensory nerve action potential (SNAP) amplitude and for conduction velocity (CV), the relative sensitivity of each parameter and the extent of concordance between them within each diabetic group were investigated. In mild neuropathy it was found that: 1) 43% (ID group) and 39% (NID group) had abnormalities of both parameters in both nerves; 2) 10% of MDC nerves and 12% of sural nerves were normal; 3) only 48% of the nerves studied had abnormalities of both parameters; 4) single parameter abnormalities were found with equal frequency. It is concluded that: 1) there is a high degree of concordance between corresponding parameters of the two nerves within each diabetic group; similar abnormalities occur within each group but are manifested at an earlier age in the ID group. 2) In mild diabetic neuropathy, (A) greater than 10% of sensory nerves studied may be normal; (B) less than 50% of nerves studied will have abnormalities of both parameters; (C) since single parameter abnormalities occur with almost equal frequency, both parameters should be taken into account for correct interpretation; (D) the evaluation of both parameters in two lower extremity sensory nerves increases diagnostic sensitivity.