Motor unit number estimate of distal + proximal muscles in CMT research

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Abstract from Muscle and Nerve May 2003

Motor unit number estimate of distal and proximal muscles in

Charcot-Marie-Tooth disease

A. , MD 1 *, Jun Li, MD, PhD 1, Darren R. Fuerst, PhD 1,

E. Shy, MD 1 2, Krajewski, MS 1 2 1Department of

Neurology, Wayne State University School of Medicine, 4201 St. Antoine,

Detroit, Michigan 48201, USA 2Center for Molecular Medicine and

Genetics, Wayne State University School of Medicine, Detroit, Michigan,

USA

Funded by:

Muscular Dystrophy Association

Charcot-Marie-Tooth Association

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.