Sensitivity and specificity of terminal latency index and residual latency in the diagnosis of carpal tunnel syndrome.

OBJECTIVES: Traditionally, nerve conduction study (NCS) are used to diagnose carpal tunnel syndrome (CTS). However, no NCS has the sufficient sensitivity or specificity values to diagnose CTS by itself. Median terminal latency index (mTLI) and median residual latency (mRL) are parameters that calculated to identify abnormalities in distal segments of the median motor nerve. There are few studies on mTLI and mRL in the diagnosis of CTS. The objective of this study was to examine the sensitivity and specificity of mTLI and mRL together with NCS in the diagnosis of CTS. PATIENTS AND METHODS AND RESULTS: The diagnostic sensitivity of mTLI and mRL were calculated and compared with the conventional NCS. Sensitivity values of electrophysiological findings were as follows: median distal sensory latency (mDSL) 91.5%, fourth finger median-ulnar sensory (M4-U4) latency difference 91.5%, mTLI 90.1%, median sensory nerve conduction velocity (mSNCV) 87.4%, and median motor distal latency (mMDL) 68.6%. Specificity values of electrophysiological findings in those with carpal tunnel syndrome were mSNCV 98.6%, mMNCV (median motor nerve conduction velocity) 98.6%, median motor wrist muscle action potential amplitude 98.6%, median sensory nerve action potential amplitude 97.4%, mSDL 97.3% and M4-U4 (fourth finger median-ulnar sensory peak latency difference) latency difference 97.3%. In all CTS patients with long mMDL values, mTLI was found to be lower, however in 22 CTS patients (22.6%) with normal mMDL, mTLI was also found to be lower. Compared with mMDL, the sensitivity of mTLI in the diagnosis of CTS was found to be higher but its specificity was lower. No differences were found in the sensitivity and specificity of mRL and mMDL. The electrophysiological findings with the highest sensitivity and specificity in diagnosing CTS among conventional NCS were mSDL, M4-U4 peak latency difference and mSNCV. CONCLUSIONS: It was concluded that mTLI and mSDL can complete each other in the detection of abnormalities of sensory and motor fibres in the diagnosis of CTS.