Stimulation of the median nerve in the palm may be a useful addition to the conventional method of stimulation above the carpal tunnel for assessing a lesion of the median nerve through the carpal tunnel. It may be particularly beneficial in cases where the median sensory nerve action potential (SNAP) cannot be obtained because of advanced sensory deficits or in cases of acute carpal tunnel syndrome (CTS). It may also lead to the adoption of new normal values for amplitude measurements of the median nerve compound muscle action potential(CMAP) recorded from the abductor pollicis brevis muscle (APB). Currently, normal values vary from as low as a few millivolts (mV) to as high as 20 mV. This primary purpose of this study is to establish a technique for stimulating the motor branch of the median nerve in the palm. In addition, we will report normal values for latency and amplitude and calculate the motor nerve conduction velocity (MNCV) across the carpal tunnel in the wrist to palm segment.
