Background: Heat sensitivity and cognitive deficits are typical manifestations of multiple sclerosis (MS). Although cognitive deficits are quite well characterized, practically no data exist on the effects of heat on cognitive performances in MS.
Objective: To assess the effects of short-term heat stress on cognitive functioning in subjects with MS.
Methods: A total of 23 heat-sensitive MS and 19 healthy control (HC) subjects participated. Moderate heat exposure took place in a Finnish sauna. Cognitive functioning was measured with tests of sustained attention and processing speed, the Paced Auditory Serial Addition Test (PASAT 3" and 2") and the computerized visual vigilance test, before, during and after heat exposure.
Results: During the heat exposure, the core body temperature of the MS group rose significantly more (p = 0.002) than that of the HC group. The heat stress worsened the performance of the MS group in the PASAT 3" (p = 0.025) but not in the other cognitive measures. The performance in the PASAT 3" was reversed almost to the baseline level only 1- h after the heat exposure.
Conclusions: A significant increase in core body temperature during heat stress is associated with a mild and reversible worsening of the PASAT 3" performance, while visual vigilance performance seems to remain almost unaffected.