Usefulness of Terminal Latency Index in Diagnosis of Carpal Tunnel Syndrome

J Korean Assoc EMG Electrodiagn Med 2006;8(2):85-90.
Published online May 10, 2006.

Abstract

Objectives: The electrophysiology of the carpal tunnel syndrome (CTS) has been extensively studied, but no single measure or combination of measures has adequate diagnostic sensitivity and specificity. 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 (NCV). We undertook this study to assess the validity of the median nerve TLI in evaluation of CTS. Methods: We prospectively evaluated 67 consecutive clinical CTS patients (104 hands) to assess the sensitivity of the median nerve TLI for the diagnosis of CTS. Control data of nerve conduction study (NCS) parameters were obtained from 21 healthy persons (38 hands). Results: The mean TLI was 0.24±0.06 in the CTS group and 0.37±0.03 in the control group (P<0.05). The calculated lower limit of normal TLI from the control group (mean-2SD) was 0.31. The sensitivity of the TLI for the diagnosis of CTS was 83.7%. Twenty hands (19%) had a normal III-W (from middle finger to wrist) SNCV, fifteen hands (14%) had a normal median TL (median motor terminal latency), 14 hands (13%) had a normal P-W (from palm to wrist) SNCV, and 9 hands (9%) had a normal ML-UL (median-ulnar sensory conduction difference) with an abnormal TLI. The TLI was the only abnormal electrophysiological parameter in seven cases (7%) from the CTS group. Conclusion: Our study showed the TLI is a useful, sensitive electrophysiologic measure for the presence of CTS.

Key Words: Carpal tunnel syndrome, Terminal latency index, Nerve conduction study, Sensitivity