CMT 1A: Motor axon loss is associated with hand dysfunction

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NEUROLOGY 2008;71:1254-1260

Motor axon loss is associated with hand dysfunction in Charcot-Marie-

Tooth disease 1a

A. J. Videler, MSc, PT, J. P. van Dijk, BSc, A. Beelen, PhD, M. de

Visser, MD, PhD, F. Nollet, MD, PhD and I. N. van Schaik, MD, PhD

From the Departments of Rehabilitation (A.J.V., A.B., F.N.) and

Neurology and Clinical Neurophysiology (M.d.V., I.N.v.S.), Academic

Medical Center, University of Amsterdam; and Department of Clinical

Neurophysiology (J.P.v.D.), Radboud University Nijmegen, Donders

Centre for Neuroscience, Medical Center, Nijmegen, the Netherlands.

Background: Charcot Marie Tooth type 1a (CMT1a) is a primarily

demyelinating neuropathy, characterized by slowly progressive muscle

weakness, atrophy, and sensory loss, and is most pronounced in both

feet and hands. There is increasing evidence that muscle weakness is

determined by motor axonal dysfunction.

Objective: To investigate in patients with CMT1a whether motor axon

loss, as estimated with motor unit number estimation (MUNE) and

compound muscle action potential (CMAP), is related to hand function

and manual dexterity.

Methods: Hand function, manual dexterity, and axon loss were studied

in 48 patients with proven CMT1a. Using high-density surface EMG on

the thenar muscles, MUNE was determined and CMAPs were measured.

Results: Pinch strength, clawing of the fingers, and manual dexterity

correlated significantly with MUNE and CMAP (amplitude and area),

while sensory impairments did not. Grip strength correlated

significantly with CMAP amplitude but did not become significant with

MUNE and CMAP area. Neurophysiologic variables were particularly

associated with fine motor function of the hand.

Conclusions: Motor axon loss is likely to be the major cause of hand

dysfunction and impaired manual dexterity in Charcot Marie Tooth type

1a (CMT1a). In a clinical setting, the evaluation of the hands of

patients with CMT1a should thus be mainly directed toward the

evaluation of fine motor functions.

Abbreviations: AROM = active range of motion; CMAP = compound muscle

action potential; CMT1a = Charcot-Marie-Tooth type 1a; HDsEMG = high-

density surface EMG; MNCV = motor nerve conduction velocity; MUAP =

motor unit action potential; MUNE = motor unit number estimation; MUP

= motor unit potential; PROM = passive range of motion; SHT =

Sollerman hand function test; SNAP = sensory nerve action potential;

SWM = Semmes-Weinstein monofilaments.