Studies of hyperthermia in optic neuropathy. Consideration of a humoral factor

Three patients with multiple sclerosis and prominent Uhthoff's symptom were studied. Visual loss was found to be related not only to increase in body temperature but to the rate of increase. Blood removed at the time of maximal visual loss and readministered in the normothermic state did not reproduce the symptom. The study supports the prevailing concept that Uhthoff's symptom is a direct effect of hyperthermia on conduction in damaged axons.