Terminal Latency lndex in the Diagnosis of Carpal Tunnel Syndrome

Abstract

Besides the standart measurement of median distal motor latency and sensory conductionvelocity, many other techniques have been developed to improve the diagnosis of carpal tunnel syndrome (CTS). 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. A value of 0.34 or greater is considered normal for the median nerve. This value is reported to be lower than 0.34 in CTS. Segmenter and comparative measurements and TLIs have been evaluated in 137 patients with clinical CTS diagnosis and 15 healthy subjects in this study. The measurements in healthy subjects havebeen performed bilaterally in sum of 30 hands. The patients whom electrophysiologically ulnar neuropathy has been found, 20 in number, have been discarded from the study. Of remaining 117 patients, in 9 2 patients, one or more of the criterias of prolongation of median distal motor latency, abnormal sensorial conduction velocity in finger-wrist or palm-wrist segment have been present, so in these patients the diagnosis CTS has been confırmed electrophysiologically. We have found that TLI was lower than 0.34 in afipatients with electrophysiologic diagnosis of CTS and in 18 of the remaining patients. We have calculated TLI greater than 0.34 in all hands studied as control in healthy subjects. We have found that the duration of symptoms were shorter in 18 patients whose only TLI values were abnormal, than those of eleetrophysiologically determinedCTS patients (U=466.5, P<0.005). This makes us to think that TLI can be an early sign of CTS.