Diagnostic Sensitivity and Specificity of Residual Latency and Terminal Latency Index in the Diagnosis of Carpal Tunnel Syndrome

ABSTRACT

BACKGROUND: Conventional nerve conduction studies (NCS) are used in the diagnosis of carpal tunnel syndrome (CTS). The median terminal latency index (TLI) and median residual latency (RL) are parameters calculated to identify abnormalities in distal segments of the median motor nerve. The objective of this study was to determine the sensitivity and specificity of TLI and RL together with NCS in the diagnosis of CTS. METHODS: This prospective study involved 83 hands of 47 patients with suspected CTS. Conventional NCS were performed using Oh's method. Control data were obtained from the 68 hands of 40 healthy volunteers. The diagnostic sensitivity and specificity of TLI and RL were calculated and compared with those of conventional NCS. We divided the CTS patients into four groups based on their electrophysiological severity, and compared the TLI and RL values between these groups. RESULTS: TLI and RL were 0.20+/-0.03 (mean+/-SD) and 3.62+/-0.90, respectively, in the patients, while the corresponding values, in the healthy control, were 0.29+/-0.03 and 2.08+/-0.30. The sensitivities of TLI and RL in diagnosing CTS were 75.9% and 86.3%, respectively. Compared with median motor terminal latency, the sensitivities of TLI and RL in diagnosing CTS was found to be higher. Moreover, the diagnostic sensitivities of TLI and RL were significant better for the severe group than for the mild and moderate severity group. CONCLUSIONS: We conclude that measuring TLI and RL of the median nerve may increase the sensitivity in diagnosing CTS and also provide information about its electrophysiological severity.