Effects of exercise-induced increases in body temperatures on local skin thermal sensitivity in Multiple Sclerosis patients

Exercise and concomitant increases in body temperature reduces local skin thermal sensitivity via hypothesized analgesic-effects. Abnormal thresholds for thermal sensations and heat-sensitivity are well-established symptoms and modulatory factors, respectively, of Multiple Sclerosis. However, it is unknown whether increases in body temperature modulate sensory abnormalities in MS. We therefore investigated the hypothesis that changes in local skin thermal sensitivity are reduced in relapsing-remitting MS patients during cycling in the heat (30°C; 35%RH). Seven MS patients (age 54±7 y; body mass 76.1±10.9 kg; body surface area 1.9±0.2 m2), with increased warmth thresholds (0.61±0.58°C) compared to 4 age-, mass- and body surface area-matched healthy controls (CTR) (53±9 y; 75.6±14.0 kg; 1.9±0.2 m2; warmth threshold: 0.38±0.25°C); were asked to perform 30-min cycling at an intensity of 3.3 W/kg of total body mass. A quantitative thermo-sensory test, consisting of reporting (visual analogue scale) perceived magnitude of local warm (38°C) and cold (22°C) thermal stimuli (25 cm2-thermal probe) applied to the dorsum of the hand, was performed before and after every 10 min of cycling. Rectal temperature increased similarly between MS (+0.20±0.17°C) and CTR (+0.15±0.09°C) (p=0.619), whereas changes in mean skin temperature were greater in MS (1.41±0.38°C) than CTR (0.96±0.28°C) (p=0.077). 30 min of cycling reduced CTR thermo-sensitivity to warm (−10.5±10.0%) and cold (−14.1±8.5%) thermal stimuli. MS patients also experienced exercise-induced reductions in local thermo-sensitivity, however these were of smaller magnitude, both for warm (−2.7±16.4%) and cold (−10.4±8.6%) thermal stimuli. In line with previous research, exercise-induced increases in body temperature reduce skin thermo-sensitivity providing an analgesic effect in healthy controls. However, MS diminishes the magnitude of such effect.