Rationale: Electrodiagnostic assessment of the median nerve is one of the most commonly used parameters in clinical electrophysiology and is routinely used to assess for carpal tunnel syndrome (CTS). However, few studies have looked at the velocity and amplitude changes of the median motor nerve when stimulating at the wrist and palm. Purpose: The purpose of this study was to establish normative values for palm and wrist amplitudes and conduction velocity across the wrist for median motor nerve transcarpal testing using a unique technique. Compound muscle action potentials (CMAPs) were recorded at the palm and wrist from normal subjects and were analyzed to established the normative data for transcarpal velocities and amplitudes. Research Goals: The goal of this research was to determine normative CMAP latencies, amplitudes and conduction velocities for transcarpal median motor nerve conduction using a unique approach. We also determined if there was a difference in amplitudes between the palm and wrist sides in normal subjects. Population: 70 hands from 35 healthy, symptom free, volunteer subjects betwen the ages of 24 to 49 without history or signs/symptoms of pathology to the median nerve. Method: While recording from the abductor pollicis brevis (APB) muscle, supramaximal stimulation was first applied in the mid-palm where the tip of the flexed ring finger touches the thenar crease. A second, supramaximal stimulation was applied at the wrist, 8cm proximal to the palm site along the course of the median nerve. Results: An independent t-test showed no statistical difference in the amplitude of the compound muscle action potentials from the palm and wrist. Normal palm latency was 2.07 msec plus or minus .60. Normal wrist latencywas 3.66 msec plus or minus .66. Normative values for palm and wrist amplitude as well as conduction velocity across the wrist were also determined using the mean plus or minus 2 SD. Normal palm amplitude was determined to be 10.18 plus or minus 4.48mV. Normal wrist amplitude was 9.63 plus or minus 4.08 mV. Normal conduction velocity between wrist and palm is 50.40 plus or minus 7.16 m/sec. The technique used was found to have a desired intrarater reliability based on the results of the intraclass correlation coefficient (ICC) testing, amplitude ICC=.94 and conduction velocity IC=.92. Conclusions: This paper provided a new and unique approach to transcarpal median motor nerve testing and provided a set of normative data.
