Abstract
In general, configuration of M-wave shows a simple dome-shape by belly-tendon montage. The M-wave recorded over the hypothenar eminence elicited by ulnar naerve stimulation often has double peaks in the negative phase. The origin of this double-peaked response has not been clarified. To investigate the origin of these double peaks, we recorded ulnar M-waves from abductor digiti minimi, 1st dorsal interossei, and adductor pollicis simultaneously in 11 hands of six normal volunteers, in two cases of Guyon's canal syndrome and in two cases of ulnar nerve injury at the wrist. In the seven hands of normal volunteers, we recorded double-peaked M-waves from abductor digiti minimi. The latency of the second peak corresponded to the peak latency of the 1st dorsal interossei and adductor pollicis. In the two cases of Guyon's canal syndrome and in the two cases of ulnar nerve injury at the wrist, M-waves from abductor digiti minimi were a simple domeshape. In those cases M-waves from the 1st dorsal interossei and adductor pollicis were almost absent. We concluded that M-waves from the 1st dorsal interossei and adductor pollicis influenced the second peak of the M-wave recorded over the hypothenar eminence.
