Body temperatures, thermal comfort, and neuropsychological responses to air temperatures ranging between 12°C and 39°C in people with Multiple Sclerosis.

The negative effects of thermal stress on Multiple Sclerosis (MS)' symptoms have long been known. However, the underlying mechanisms of MS heat and cold intolerance remain unclear. The aim of this study was to evaluate body temperatures, thermal comfort, and neuropsychological responses to air temperatures between 12 and 39 °C in people with MS compared to healthy controls (CTR). Twelve MS (5 males/7 females; age: 48.3 ± 10.8 years; EDSS range: 1-7) and 11 CTR participants (4 males /7 females; age: 47.5 ± 11.3 years) underwent two 50-min trials in a climatic chamber. Air temperature was ramped from 24 °C to either 39 °C (HEAT) or 12 °C (COLD) and we continuously monitored participants' mean skin (T) and rectal temperatures (T), heart rate and mean arterial pressure. We recorded participants' self-reported thermal sensation and comfort, mental and physical fatigue, and we assessed their cognitive performance (information processing). Changes in mean T and T did not differ between MS and CTR neither during HEAT nor COLD. However, at the end of the HEAT trial, 83% of MS participants and 36% of CTR participants reported being "uncomfortable". Furthermore, self-reports of mental and physical fatigue increased significantly in MS but not CTR (p < 0.05), during both HEAT and COLD. Information processing was lower in MS vs. CTR (p < 0.05); yet this cognitive impairment was not exacerbated by HEAT nor COLD (p > 0.05). Our findings indicate that neuropsychological factors (i.e. discomfort and fatigue) could contribute to MS heat and cold intolerance in the absence of deficits in the control of body temperature.