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Motor axon loss is associated with hand dysfunction in Charcot-Marie-Tooth disease 1a

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.

Address correspondence and reprint requests to Drs. Annemieke J. Videler, Department of Rehabilitation, A01-415, Academic Medical Center, University of Amsterdam, PO Box 22660, 1100 DD Amsterdam, the Netherlands a.j.videler{at}amc.uva.nl

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.

Supplemental data at www.neurology.org

Disclosure: The authors report no disclosures.

Received April 2, 2008. Accepted in final form July 14, 2008.