PROBLEMS IN THE MOTOR NERVE CONDUCTION STUDY

Abstract

Motor nerve conduction studies of the median and ulnar nerves were carried out in twenty healthy normal subjects by conventional techniques. The amplitude of motor action potential (M-wave) and the distal motor latency time were measured by stimulating at the wrist. The amplitude from negative to positive peak was considered to the M-wave response. The time from stimulus artifact to the first deflection was taken as the distal motor latency time.The pick-up electrode was firstly placed on the middle portion of the muscle belly and the conduction study was performed, then the pick-up electrode was placed 1cm distally and same study was carried out. Thus, the amplitude and latency time were compared according to the different site of pick-up electrodes.The results were shown in the following table:In 1cm distal part of muscle belly, the amplitude of M-wave was approximately 70% of that of the middle portion in both median and ulnar innervated muscles. But distal motor latency times at the two different portions were statistically unchanged.It is concluded that the distal motor latency time is more valuable indicator in motor nerve conduction study. Also if the pick-up electrode was placed precisely over the middle of muscle belly tested, the amplitude of M-wave is reproducible, then it will become good indicator in motor nerve conduction study.