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.