Defective E2 electrode lead gives low-amplitude compound muscle action potential.

E1 and E2 electrodes contribute to the CMAP. A defective recording electrode lead to E1 or E2 results in a low-amplitude CMAP. The amplitude drop observed with a disconnected E2 lead was far greater than the signal recorded by the E2 electrode. This occurs due to the amplifier's inherent property to reduce the voltage difference between the E1 and E2 inputs. When E2 lead is defective, the CMAP will be an attenuated version of the signal recorded by the E1 electrode, and vice versa. When low-amplitude CMAP amplitude is observed in all conduction studies, technical artifact should be considered before exploring the pathological basis for the abnormal results.