Are the sensory and motor nerve fibers affected differently in carpal tunnel syndrome? A comparative electrophysiological study

Although the exact pathophysiology of carpal tunnel syndrome (CTS) is not clear yet, most of the studies supported that there is a preferential sensory fibers involvement with sparing of motor fibers, especially in mild forms. In this study, we aimed to investigate the frequency of motor fiber involvement and compare the sensitivities of nerve conduction studies reflecting the functions of motor and sensory fibers in CTS. Patients with the initial clinical diagnosis of idiopathic CTS were evaluated prospectively and those found to have severe CTS after the electromyographic study were excluded. Both hands of 100 patients and 50 healthy volunteers were investigated. We found that the weight, body mass index, hand width, mediolateral dimension of the wrist and wrist ratio were higher in the patient group. In the electromyographic study, 33% of the hands were normal in all electrophysiological studies, 21% of the hands were abnormal only in the comparative tests, 11,5% of the hands had normal median distal motor latency (DML) with slowing of the median sensory conduction and 34,5% of the patients had abnormal median DML in company with slowing of the median sensory conduction. Both second lumbrical-interossei motor and the median-ulnar sensory comparative studies had the highest sensitivities, with similar results which were followed by the median sensory and motor studies, respectively. Our study implies that even in mild and moderate forms of CTS, it is more reasonable to think that motor and sensory fibers are equally involved rather than assuming the preferential involvement of sensory fibers.