Conduction study in human muscle fibers in situ--a useful technique for diagnosing myopathies

Direct muscle conduction studies were carried out using monopolar needle electrodes in the distal portion of the brachial biceps muscles in 13 normal and 10 myopathic subjects. Two monopolar Teflon-coated needles with exposed tips were placed as stimulation electrodes in the distal end of the biceps muscle. A pick-up monopolar electrode was then placed 4 cm proximal to the stimulation electrodes along the same muscle with a surface reference electrode in the vicinity of the active electrode. After the maximal evoked response was detected, the shape, amplitude and duration were recorded. The results revealed that the muscle conduction velocity was slower in polymyositis patients compared with normal subjects but was not significantly different in patients with progressive muscular dystrophy. However, the shape, amplitude and duration of the muscle-evoked potential were characteristic in the myopathies. It is concluded that this muscle conduction study technique is simple and of clinical use in making electrodiagnosis.