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Heating and Eye Movements Model Nerve Conduction in MS

Impairment in ocular function worsens after heating and is restored on cooling

TUESDAY, March 25 (HealthDay News) -- In multiple sclerosis (MS) patients with a particular defect in eye movement, whole-body heating further impairs ocular motor function that is restored after cooling, providing a model for changes in the fidelity of axonal conduction, according to a study published in the March 25 issue of Neurology.

S.L. Davis, Ph.D., from the University of Texas Southwestern Medical Center at Dallas, and colleagues measured ocular motor function at 10-minute intervals in eight MS patients with internuclear ophthalmoparesis, eight MS patients without internuclear ophthalmoparesis and eight matched, healthy controls. Measurements were taken at normothermic baseline, during whole-body heating and after whole-body cooling.

The researchers found that the versional disconjugacy index (ratio of abducting/adducting eye movements for velocity) and first pass amplitude (position of the adducting eye when the abducting eye achieves a centrifugal fixation target) increased after whole-body heating in MS patients with internuclear ophthalmoparesis and returned to baseline values after cooling. The increases after heating confirm "a compromise in axonal electrical impulse transmission properties" and the return to baseline on cooling confirms "the reversible and stereotyped nature of this characteristic feature of demyelination," the authors note.

"We have developed a neurophysiologic model for objectively understanding temperature-related reversible changes in axonal conduction in multiple sclerosis," Davis and colleagues conclude. "Our observations corroborate the hypothesis that changes in core body temperature (heating and cooling) are associated with stereotypic decay and restoration in axonal conduction mechanisms."

One of the study authors reports a financial relationship to Biogen Idec, TEVA and Serono.

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