Terminal Latency Index of the Median Nerve: 
Normal Values and Relation to Carpal Tunnel Syndrome

J Korean Neurol Assoc > Volume 22(6); 2004 > Article

Journal of the Korean Neurological Association 2004;22(6): 609-612.

정중신경의 말단 잠복기 지수: 정상치와 수근관증후군과의 관계

강사윤, 최재철 강지훈

제주대학교 의과대학 신경과학교실

Terminal Latency Index of the Median Nerve: Normal Values and Relation to Carpal Tunnel Syndrome

Sa-Yoon Kang

Department of Neurology, Cheju National University College of Medicine, Jeju, Korea

Abstract

Background: The terminal latency index (TLI) is a calculated value that adjusts the distal motor latency for the terminal distance and the proximal motor nerve conduction velocity. The purpose of this study is to evaluate the sensitivity of the median TLI in the diagnosis of carpal tunnel syndrome (CTS) and compare it with other electrophysiological parameters.
Methods: We prospectively studied 32 patients with nerve conduction studies using a conventional surface technique in the median and ulnar nerves. The distal distance for the CMAP was measured in 5 츠 using Oh's techniques. Based on the clinical diagnosis, 32 patients (59 hands) were judged to have CTS. Control data were obtained from 40 healthy hands utilizing identical techniques.
Results: The mean TLI was 0.24±0.04 in the CTS group and 0.30±0.02 in the control group (P<0.01). The 32 patients had a mean age of 57 years (SD±13 years; 73% women). Twenty subjects with an average age of 46 years (SD±15 years; 65% women) were evaluated for control data. The calculated lower limit of normal from the control group (mean-2SD) was 0.26. The sensitivity of the TLI was 73%. The TLI was statistically better than the median motor distal latency and sensory nerve conduction velocity in the second digit-wrist segment. In four patients from the CTS group, the TLI was the only abnormal electrophysiological parameter.
Conclusions: The median TLI is an easy, inexpensive, highly informative test and is therefore extremely useful in the diagnostic work-up of patients with CTS.Key Words: Nerve conduction, Carpal tunnel syndrome, Median nerve, Sensitivity