Terminal Latency Index, Residual Latency, and Median-Ulnar F-Wave Latency Difference in Carpal Tunnel Syndrome

Ann Indian Acad Neurol. Apr-Jun 2019;22(2):175-179. doi: 10.4103/aian.AIAN_276_18.


Introduction: Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy, but no electrodiagnostic test alone shows sufficient sensitivity for CTS. We aimed to investigate the value of median motor terminal latency index (mTLI), median motor residual latency (mRL), and median-ulnar F-wave latency difference (FdifMU) as additional tests to nerve conduction studies which are performed traditionally in electromyography laboratories.

Methods: This is a retrospective study. The results of electrodiagnostic studies performed on patients with CTS were examined. We divided the enrolled hands of the patients diagnosed with CTS into two groups: affected hands with abnormal electroneuromyographic parameters indicating CTS diagnosis (CTS group) and hands with normal electroneuromyographic parameters (control group). Then, we analyzed the results of these completed electrodiagnostic studies.

Results: A total of 320 hands of 160 patients were studied. FdifMU and mRL were found to be significantly higher in CTS group compared with the control group (P < 0.001). mTLIs were found to be significantly higher in control group compared with the CTS group (P < 0.001). Given that, the area under the curve is more than 70% for mTLI and mRL, but not for FdifMU.

Conclusion: When combined with mMDL, both mTLI and mRL have excellent specificity for the diagnosis of mild and moderate CTS. However, the sensitivities for both parameters were lower. In suspected patients, FdifMU can be an additional tool for the diagnosis of CTS also, but alone it is not valuable.

Keywords: Carpal tunnel syndrome; F-wave latency; residual latency; terminal latency index.