Afferent thermosensory function in relapsing-remitting multiple sclerosis following exercise-induced increases in body temperature

In multiple sclerosis (MS), increases in body temperature result in transient worsening of clinical symptoms (heat-sensitivity/Uhthoff's phenomenon). While the impact of heat-sensitivity on efferent physiological function has been investigated, the effects of heat stress on afferent sensory function in MS are unknown. Hence, we quantified afferent thermosensory function in MS following exercise-induced increases in body temperature with a novel quantitative sensory test. Eight relapsing-remitting MS patients (3M/5F; 51.4 ± 9.1 y; EDSS score: 2.8 ± 1.1) and 8 age-matched controls (CTR; 5M/3F; 47.4 ± 9.1 y) rated perceived magnitude of two cold (26; 22°C) and warm (34; 38°C) stimuli applied to the dorsum of the hand, pre and post 30-min cycling in the heat (30°C air; 30% RH). Exercise produced similar increases in mean body temperature in MS (+0.39°C [95%CI: +0.21, +0.53] P = 0.001) and CTR (+0.41°C [95%CI: +0.25, +0.58] P = 0.001). These changes were sufficient to significantly decrease thermosensitivity to all cold (26°C stimulus: -9.1% [95%CI: -17.0, -1.5], P = 0.006; 22°C stimulus: -10.6% [95%CI: -17.3, -3.7], P = 0.027), but not warm, stimuli in MS. Contrariwise, CTR showed sensitivity reductions to colder stimuli only (22°C stimulus: -9.7% [95%CI: -16.4, -3.1], P = 0.011). The observation that reductions in thermal-sensitivity in MS were confined to the myelinated cold-sensitive pathway, and extended across a wider (including milder/colder) temperature range than what is observed in CTR, provides novel evidence on the impact of rising body temperature on afferent neural function in MS. Also, our findings support the use of our novel approach to investigate afferent sensory function in MS during heat stress. This article is protected by copyright. All rights reserved

Cold water ingestion improves exercise tolerance of heat-sensitive people with MS

© 2018 Lippincott Williams and Wilkins. All rights reserved. Purpose Heat intolerance commonly affects the exercise capacity of people with multiple sclerosis (MS) during bouts of hot weather. Cold water ingestion is a simple cooling strategy, but its efficacy for prolonging exercise capacity with MS remains undetermined. We sought to identify whether cold water ingestion blunts exercise-induced rises in body temperature and improves exercise tolerance in heat-sensitive individuals with MS. Methods On two separate occasions, 20 participants (10 relapsing-remitting MS (expanded disability status scale, 2-4.5); 10 age-matched healthy controls) cycled at ∼40% VO 2max at 30°C and 30% relative humidity until volitional exhaustion (or a maximum of 60 min). Every 15 min, participants ingested 3.2 mL·kg -1 of either 1.5°C (CLD) or 37°C (NEU) water. Rectal (T re ) temperature, mean skin (T sk ) temperature, and heart rate (HR) were measured throughout. Results All 10 controls but only 3 of 10 MS participants completed 60 min of exercise in NEU trial. The remaining 7 MS participants all cycled longer (P = 0.006) in CLD (46.4 ± 14.2 min) compared with NEU (32.7 ± 11.5 min), despite a similar absolute T re (NEU: 37.32°C ± 0.34°C; CLD: 37.28°C ± 0.26°C; P = 0.44), change in T re (NEU: 0.38°C ± 0.21°C; CLD: 0.34°C ± 0.24°C), absolute T sk (NEU: 34.48°C ± 0.47°C; CLD: 34.44°C ± 0.54°C; P = 0.82), and HR (NEU: 114 ± 20 bpm; CLD: 113 ± 18 bpm; P = 0.38) for the same exercise volume. Conclusions Cold water ingestion enhanced exercise tolerance of MS participants in the heat by ∼30% despite no differences in T re , T sk or HR. These findings support the use of a simple cooling strategy for mitigating heat intolerance with MS and lend insight into the potential role of cold-afferent thermoreceptors that reside in the abdomen and oral cavity in the modulation of exercise tolerance with MS in the heat

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