axonal loss assessment research

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Abstract from Exp Neurol. 2003 Dec;184(2):753-7.

Assessment of axonal loss in Charcot-Marie-Tooth neuropathies.

Lawson VH, Gordon A, Bromberg MB.

Department of Neurology, University of Utah School of Medicine, Salt

Lake City, UT 84132, USA.

Sensory loss and weakness in Charcot-Marie-Tooth (CMT) neuropathy is due

to axonal loss. However, the pattern and degree of axonal loss cannot be

accurately determined from routine electrodiagnostic or strength testing

due to collateral reinnervation. We sought to quantify axonal loss in

two upper extremity muscles in CMT1A and CMT2 subjects using the

electrophysiologic endpoint measure of motor unit number estimation

(MUNE).

Hypothenar and biceps-brachialis muscle groups were studied in 9 CMT1A,

9 CMT2, and 10 control subjects. The spike-triggered averaging (STA)

technique was used to collect surface motor unit potentials for MUNE

calculations, and a needle electrode was used to

collect corresponding intramuscular data. Maximal voluntary hypothenar

and handgrip strength was measured quantitatively, while

biceps-brachialis strength was measured qualitatively.

Compared to normal subjects, CMT1A and CMT2 subjects had significantly

lower MUNE values in hypothenar muscles. Biceps-brachialis MUNE values

were reduced in CMT2 but not in CMT1A subjects. In support of proximal

axonal loss in CMT2 subjects, surface motor unit and intramuscular

potential amplitudes were higher in biceps-brachialis muscles compared

to controls.

Correlations between quantitative strength and MUNE were significant for

hypothenar but not for grip muscle groups. Axonal loss is demonstrated

in distal muscles in CMT1A and CMT2 supporting a length-dependent

axonopathy. Despite clinical findings of normal or near-normal strength

and small reductions in compound muscle action potential (CMAP)

amplitude, MUNE values were significantly lower in CMT2 subjects in

proximal muscles, consistent with more diffuse denervation. These data

indicate that subclinical axonal loss is present that cannot be

appreciated using clinical examination or routine electrodiagnostic

techniques.