Assessment of Cutaneous Silent Period in Diabetic Polyneuropathy

J Korean Assoc EMG Electrodiagn Med 2003;5(2):82-86.
Published online May 10, 2003.

Abstract

Objectives: A single cutaneous electrical stimulus inhibits tonically firing motor neurons resulting in a silent period (cutaneous silent period, CSP) in electromyographic activity. Most investigators agree the afferent impulses that generate the CSP are carried by A-delta fibers. To assess dysfunction in these smaller, slower-conducting fibers in diabetic polyneuropathy, the CSP was evaluated. Methods: Thirty-six patients with diabetes and 13 healthy normal subjects were studied. CSP was recorded over the abductor pollicis brevis muscle on stimulating the fifth finger. Nerve conduction studies and sympathetic skin response (SSR) measurements for comparison were performed. Results: In diabetic patients with polyneuropathy, the onset of the CSP was 92.1±14.4 ms and the endpoint was 130.1±17.6 ms. In diabetic patients without polyneuropathy, the onset was 88.0±9.6 ms and the endpoint was 125.9±15.0 ms. The latencies of the CSP were not significantly different in diabetic patients with or without polyneuropathy compared with healthy controls. The SSR was performed in 32 diabetic patients. In six of the 32 patients, the SSR was absent. Though the onset of the CSP seemed prolonged in the patient without SSR (101.2±3.6 ms), the latencies were not different statistically. In the remaining 26 patient with SSR, the latencies of the CSP did not differ significantly from healthy controls. Conclusion: The latencies of the CSP in diabetic patients were not clearly related to nerve conduction findings and SSR. Although CSP testing may complement routine nerve conduction studies as a test of small fiber function abnormalities this seemed relatively insensitive to mild degree of peripheral nerve dysfunction.

Key Words: Cutaneous silent period, Sympathetic skin reflex, Diabetic polyneuropathy