Clinical disease severity and axonal dysfunction in HMSN/CMT 1A

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Abstract from J Neurol. 2004 Dec;251(12):1491-7.

Clinical disease severity and axonal dysfunction in hereditary motor and sensory

neuropathy Ia.

Verhamme C, van Schaik IN, Koelman JH, de Haan RJ, Vermeulen M, de Visser M.

Department of Neurology and Clinical Neurophysiology, H2-222 Academic Medical

Centre, University of Amsterdam, PO Box 22700, 1100, DE Amsterdam, The

Netherlands,

BACKGROUND : Hereditary motor and sensory neuropathy type Ia (HMSN Ia) is known

as a primarily demyelinating peripheral nerve disease. Evidence is accumulating

that axonal involvement determines the course of the disease process.

METHODS : Fifty-one patients were investigated. Physical disability and

impairments were scored. Nerve conduction velocities (NCVs) were used as

indirect measures for myelination status and compound muscle/sensory nerve

action potential (CMAP/SNAP) amplitudes served as indirect measures for axonal

function.

RESULTS : Median age was 39 years (range 6-69).Muscle weakness and sensory

dysfunction was more severe in the legs than in the arms and distally more than

proximally. However, more than 40% of the patients had proximal muscle weakness

in the legs. Three point grip was used as representative of combined distal arm

muscle groups. CMAP amplitude was the most important independent variable in a

multiple linear regression model (forward selection) to explain the relation

between three point grip strength and four different features, i. e., CMAP

amplitude of the abductor pollicis brevis, median nerve MNCV, gender, and

duration of signs and symptoms. The severity of axonal dysfunction was nerve

length-dependent and was related to the myelination status. The mild physical

disability due to both muscle weakness and sensory dysfunction was also related

to axonal dysfunction.

CONCLUSIONS : In HMSN Ia, clinical disease severity at the impairment and

disability levels is related to the severity of axonal dysfunction. Our data

support the hypothesis that the myelination status is one of the factors that

determine the extent of axonal dysfunction later in life. Proximal weakness of

the legs is encountered in a considerable proportion of our patients.

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