Distal sensory nerves of the lower extremity in peripheral neuropathy: comparison of medial dorsal cutaneous and sural nerve abnormalities.

This study investigates the sensitivity and usefulness of medial dorsal cutaneous nerve (MDCN) conduction studies in patients with peripheral neuropathy. Two hundred twenty-three patients with clinical signs and symptoms of peripheral neuropathy in their lower extremities were evaluated. Nerve conduction velocity studies of the MDCN were compared to those of the sural and peroneal motor nerves. Fifty-eight percent of the patients had no measurable sensory nerve action potential (SNAP) from either the MDCN or sural nerve or both, indicating moderate to severe neuropathy. Of the remaining patients with mild neuropathy, 12% had a normal sural nerve and an abnormal MDCN, whereas 7% had a normal MDCN and an abnormal sural nerve. Fifty-one percent of the mild cases had normal peroneal motor nerve studies. It is concluded that the MDCN is equal to the sural nerve as a sensitive indicator in all stages of peripheral neuropathy; in mild or early neuropathy approximately 12% of patients will have normal sural nerve studies; and it is important to examine both distal sensory nerves of the leg. Addition of the MDCN study to the standard sural study increases diagnostic accuracy in mild peripheral neuropathy from 88% to nearly 100%.