Early Detection of Diabetic Polyneuropathy Using Paired Stimulation Studies of the Sensory Nerves

OBJECTIVE: This study seeks to use the relative refractory period, a sensitive parameter for detecting early change in peripheral polyneuropathies, as a tool for early detection of diabetic polyneuropathy. DESIGN: The relative refractory period of the median and sural sensory nerves was measured in 57 diabetic patients (male 31, female 26) and 23 healthy controls (male 16, female 7). The shortest interstimulus interval, where the latency of the response to the second stimulus recovers to normal, was defined as the relative refractory period. RESULTS: The relative refractory period of the median and sural nerves were significantly longer in diabetic patients (3.6 msec, P < 0.001, and 3.8 msec, P < 0.001, respectively) than in the control group (3.0 msec in both nerves). Relative refractory period values of both nerves were also significantly prolonged compared with the control group, even in diabetic patients without diabetic polyneuropathy based on conventional conduction studies (3.3 msec, P = 0.002, for median nerve; 3.5 msec, P < 0.001, for sural nerve) or without any clinical symptoms and signs (3.3 msec, P = 0.007, for median nerve; 3.5 msec, P = 0.001, for sural nerve). CONCLUSIONS: The relative refractory period was prolonged in diabetic patients even before other electrophysiologic abnormalities or clinical findings appeared. These results suggest that the relative refractory period can be a possible early indicator of diabetic polyneuropathy.