nerve conduction in Type X - Research from Italy

January 7, 2004

From Clin Neurophysiol. 2004 Jan;115(1):64-70.

Inter-nerves and intra-nerve conduction heterogeneity in CMTX with

Arg(15)Gln mutation.

Capasso M, Di Muzio A, Ferrarini M, De Angelis MV, Caporale CM, Lupo S,

Cavallaro T, Fabrizi GM, Uncini A.

Neurodegenerative Diseases Unit, Institute of Aging, University " G.

d'Annunzio " , Ospedale " SS. Annunziata " , Via dei Vestini, I-66013.

OBJECTIVE: In X-linked Charcot-Marie-Tooth disease (CMTX),

electrophysiological and histopathological studies have suggested either

a demyelinating or an axonal polyneuropathy. We report a CMTX family

with a striking heterogeneity of nerve conductions between and within

nerves.

METHODS: Two men and one woman have been studied by conduction

velocities, sural nerve biopsy with morphometry (one man) and DNA

analysis.

RESULTS: In both men motor conduction velocities were slowed in the

demyelinating range,

conduction velocity differences among nerves in the same subject varied

from 13 to 24 m/s, and distal median compound muscle action potential

(CMAP) amplitudes were 3-5 times reduced compared to ulnar CMAPs.

Abnormal area reduction or excessive temporal

dispersion of proximal CMAP was present in at least two nerves in all

patients. Sural nerve biopsy showed reduction of large myelinated

fibres, cluster formations, occasional onion bulbs. Teased fibres study

revealed short internodes for fibre diameter, enlarged Ranvier nodes but

no evidence of segmental demyelination and remyelination. DNA

analysis showed an Arg(15)Gln mutation in connexin32 gene in all

patients.

CONCLUSIONS: In this family conduction slowing and segmental conduction

abnormalities, in absence of morphological evidence of de-remyelination,

may be related to short internodes, widened Ranvier nodes and the

specific effect of the mutation. The

occurrence in some CMTX patients of a non uniform involvement between

and within nerves, as in acquired demyelinating neuropathies, should be

kept in mind to avoid misdiagnoses.

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