N10 component in median nerve somatosensory evoked potentials (SEPs) is not an antidromic motor potential.
OBJECTIVE
To test the hypothesis that the N10 far-field potential in median nerve somatosensory evoked potentials is generated by the motor axons by examining patients with amyotrophic lateral sclerosis (ALS).


METHODS
Subjects were 5 ALS patients showing pronounced or complete denervation of median-innervated small hand muscles. We evaluated N10 over scalp, and proximal plexus volleys (PPVs) at lateral or anterior cervical electrode.


RESULTS
N10 and PPVs were definitely preserved for every ALS subject. N10 amplitudes of ALS subjects were even significantly larger than control subjects. In one ALS patient completely lacking motor axons, N10 was larger than the largest one among control subjects.


CONCLUSIONS
Present results clearly indicate that N10 is not predominantly generated by motor axons but by the whole median nerve dominated by sensory axons. We propose a theory that N10 is a junctional potential generated by the entrance of the median nerve into bone at the intervertebral foramen, producing a positive pole at the non-cephalic reference electrode. Significantly larger N10 in ALS subjects may be due to the lack of cancellation by slower motor axons.


CONCLUSIONS
The hypothesis that N10 is generated by motor axons is refuted, and a new theory of its generation is presented.
Sonoo
M
M
Department of Neurology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 1738605, Japan. sonoom@med.teikyo-u.ac.jp
Hatanaka
Y
Y
Tsukamoto
H
H
Tsai-Shozawa
Y
Y
Shimizu
T
T
D000368:Aged; D000369:Aged, 80 and over; D000690:Amyotrophic Lateral Sclerosis / Q000503:physiopathology*; D001369:Axons; D001931:Brain Mapping; D016022:Case-Control Studies; D019054:Evoked Potentials, Motor; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000503:physiopathology*; D008875:Middle Aged; D009046:Motor Neurons