Thermal sensitivity in demyelinating neuropathy.

An 8-year-old girl with demyelinating peripheral neuropathy was observed to get markedly weak coincident with a febrile illness. With return of body temperature to normal over 24 hours, her strength improved back to baseline. Subsequently, we studied the effect of temperature on CMAP amplitude of two motor nerves in the patient and two control subjects. Both temperature, measured orally, was raised by immersing the subjects in hot water and lowered by passive cooling. With increase in temperature to 39.5 degrees C, the CMAP amplitudes were reduced by 80% in the patient's nerves compared to only 48% in the control nerves. These changes recovered with cooling to 36.9 degrees C. We conclude that demyelinated peripheral nerves are more susceptible to temperature-induced impulse blocking than healthy nerves and provide the first published evidence of the clinical consequences of this phenomenon in a demyelinating disease other than multiple sclerosis.