Entrapment neuropathy of the palmar cutaneous branch of the median nerve in carpal tunnel syndrome

Objective: The aim of this study is to elucidate the significance of electrophysiological data of the palmar cutaneous branch of the median nerve (PCBm) in the diagnosis entrapment of the PCBm concomitant with carpal tunnel syndrome (CTS). Materials and Methods: Clinical and electrophysiological studies were conducted for abnormal sensation of the thenar eminence in eight CTS patients. Sensory nerve action potentials (SNAPs) of the PCBm were recorded from bipolar surface electrodes over the forearm using an orthodromic method. The preoperative SNAP evaluation was compared with the operative findings. Results: The eight patients were divided into two groups based on the characteristics of SNAPs of the PCBm; five patients had normal SNAPs of the PCBm and three patients had delayed or absent SNAPs. Open surgery confirmed entrapment of the PCBm in one patient in the first group and all patients in the latter group. Conclusions: Although clinical symptoms were not always reliable to diagnose entrapment of the PCBm in CTS, electrophysiological study of the PCBm was highly sensitive (75%) and entirely specific (100%) to demonstrate the entrapment of the PCBm preoperatively.