motor unit number estimate of CMT muscles - new Research

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Abstract from Muscle Nerve. 2003 Aug;28(2):161-7.

Motor unit number estimate of distal and proximal muscles in

Charcot-Marie-Tooth disease.

RA, Li J, Fuerst DR, Shy ME, Krajewski K.

Department of Neurology, Wayne State University School of Medicine, 4201

St. Antoine, Detroit, Michigan 48201, USA.

In order to determine the utility of motor unit number estimation (MUNE)

in assessing axonal loss in chronic inherited neuropathies, we

determined MUNEs in 54 patients with Charcot-Marie-Tooth (CMT) disease

(29 patients with CMT-1A, 13 with CMT-X, and 12 with CMT-2) by using

spike-triggered averaging (STA) of the ulnar-innervated abductor digiti

minimi/hypothenar muscles (ADM) and the musculo-cutaneous innervated

biceps/brachialis (BB) muscles. MUNEs were analyzed in relationship to

the corresponding compound muscle action potential (CMAP) amplitudes as

well as to clinical strength. Proximal muscles, which appeared strong

clinically, had evidence of chronic denervation/reinnervation, although

to a lesser extent than weak distal hand muscles, supporting the concept

that axonal loss in CMT occurs in a length-dependent fashion.The

reduction in ADM-MUNE strongly correlated with clinical weakness in

the hand. Both the ADM-MUNE and BB-MUNE were abnormal more often than

CMAP amplitude, probably reflecting extensive motor unit reconfiguration

and enlargement that maintains CMAP amplitude despite severe motor unit

loss. This study suggests that MUNE can assess motor unit loss in CMT

and may better reflect axonal loss than CMAP

amplitude. The STA technique of MUNE may be useful in longitudinal

studies of proximal and distal motor unit changes in CMT.