Regional skin wetness perception and its modulation by warm and cold whole-body skin temperatures in people with Multiple Sclerosis

Skin wetness sensing is important for thermal stress resilience. Individuals with Multiple Sclerosis (MS) present greater vulnerability to thermal stress; yet it is unclear whether they present wetness sensing abnormalities. We investigated the effects of MS on wetness sensing and their modulation with changes in mean skin temperature (Tsk). Twelve MS participants (5M/7F; 48.3±10.8y; EDSS range: 1-7), and 11 healthy controls (4M/7F; 47.5±11.3y) undertook three trials, during which they performed a quantitative sensory test with either a thermo-neutral (30.9°C), warm (34.8°C), or cold (26.5°C) mean Tsk. Participants reported on visual analogue scales local wetness perceptions arising from the static and dynamic application of a cold-, neutral-, and warm-wet probe (1.32cm2; water content: 0.8ml), to the index-finger pad, forearm, and forehead. Data were analysed for the group-level effect of MS, as well as for its individual variability. Our results indicated that MS did not alter skin wetness sensitivity at a group level, across the skin sites and temperature tested, neither under normothermia nor under conditions of shifted thermal state. However, when taking an individualised approach to profiling wetness sensing abnormalities in MS, we found that 3 out of the 12 MS participants (i.e. 25% of the sample) presented a reduced wetness sensitivity on multiple skin sites, and to different wet stimuli (i.e. cold-, neutral-, and warm-wet). We conclude that some individuals with MS may possess reduced wetness sensitivity; however, this sensory symptom may vary greatly at an individual level. Larger-scale studies are warranted to characterise the mechanisms underlying such individual variability.