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Origin of surface motor unit potentials in hypothenar motor unit number estimation
Yasuomi Kawamura1, Masahiro Sonoo, Mana Higashihara
1Department of Neurology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 1738605, Japan.
Introduction:
Far-field potentials (FFPs) from muscles other than the abductor digiti minimi (ADM) may interfere with motor unit number estimation (MUNE) from that muscle.
Methods:
We identified the origin of each surface motor unit potential (SMUP) during hypothenar MUNE using the multiple point stimulation method in 20 control subjects by recording from individual ulnar-innervated muscles with a common proximal reference (pref).
Results:
ADM SMUPs comprised 39.0% of the accepted SMUPs, followed by those from the fourth dorsal interosseous muscle (14.0%), the fourth lumbrical muscle (9.2%), and the second and third palmar interosseous muscles (8.8% each). The percentage of ADM SMUPs varied from 18% to 73% of accepted SMUPs among individual subjects. Accepted non-ADM SMUPs were usually much smaller than ADM SMUPs, and many more non-ADM SMUPs were excluded due to their small size.
Conclusions:
A large contribution from non-ADM or non-hypothenar SMUPs obscures the meaning of the MUNE value.
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