Influence of Reference Electrode Position on the Onset Latency and Amplitude of Median Nerve Compound Muscle Action Potential

J Korean Assoc EMG Electrodiagn Med 2003;5(1):28-32.
Published online May 10, 2003.

Abstract

Objective: To assess the influence of reference electrode position on the onset latency and amplitude of median compound muscle action potential (CMAP) . Method: Median motor nerve conduction study was performed in subjects consisting of 30 hands of 15 healthy individuals. With the active electrode stabilized on the thenar eminence, median motor nerve conduction study was performed with the reference electrode was placed on six different sites. Differences in onset latency and CMAP amplitude according to reference electrode placement sites were compared. A second part consisted of placing the reference electrode on the contralateral hand and the varying active electrode placement on the thenar eminence and on the six reference electrode positions previously noted. CMAP amplitude differences between the response obtained from the active electrode of the six different positions and the amplitude of the response from the thenar eminence were obtained. Results: CMAP amplitude was significantly larger with the reference electrode placed at the lateral aspect of mid portion of the proximal phalanx of thumb. Conclusion: This study demonstrates that the position of reference electrode can affect median CMAP amplitude.

Key Words: Median nerve, Compound muscle action potential, Reference electrode, Latency, Amplitude