A small negative evoked potential is often recorded before the median thenar or ulnar hypothenar compound muscle action potential(CMAP) with supramaximal stimulation and has therefore been termed the premotor potential(PMP). This PMP was first described by Simpson and attributed to a nerve action potential arising from terminal motor fibers before their muscular innervation. Several authors have since explored whether this potential arises from terminal motor nerve fibers or from sensory nerve fibers. At now investigators generally accepted the concept of the sensory nature of the PMP. The goals of this study were to explore the diagnostic availability of PMP on the patients with abnormal conventional sensory conduction studies and to determine reference values for the following characteristics of the median PMP, and ulnar PMP: amplitude, onset latency, peak latency, and the interpeak interval(IPI), which is the time between the onset of the PMP and the onset of the CMAP. |