Median Nerve Residual Latency in Normal Controls and Patients with Diabetes Mellitus

ABSTRACT

Residual latency is the difference between the expected and measured terminal latencies in nerve conduction study. The main contributors to the residual latency are the nerve tapering in the hand and fingers and the neuromuscular delay. We measured median motor and sensory residual latencies in the controls and in patients with diabetes mellitus(DM) to establish the normal values, to evaluate the diagnostic value of the residual latency in diabetic polyneuropathy. we studied 50 healthy controls and 100 diabetic patients with or without polyneuropathy. The normal residual latency values were 1.42+/-0.41 msec(mean+/-SD) in motor part and 0.44+/-0.20 msec in sensory part of median nerve. The standard deviation of residual latency in median motor nerve was decreased by 12% as compared with that of distal latency in the patient with diabetic polyneuropathy. Duration of DM and age were not related to the residual latency of median nerve. The results suggest that the residual latency of median motor nerve provides a narrower normal range in the diagnosis of diabetic polyneuropathy irrespective of duration of DM or age.