Core temperature is not elevated at rest in people with relapsing-remitting multiple sclerosis

Purpose: To reassess the notion that people with multiple sclerosis (MS) do not demonstrate an elevated resting core temperature when measured using best-practice precision thermometry. Method: Across two international data collection sites (Australia and USA), twenty-eight relapsing-remitting MS patients and 27 aged-matched controls (CON) were exposed to either 30 °C, 30% relative humidity (RH) (Sydney) or 25 °C, 30% RH (Dallas). Resting rectal (T _re ) and esophageal (T _eso ) temperature and resting oxygen consumption (VO ₂ ) was measured in MS (n = 28) and CON (n = 27) groups who completed the 25 °C and 30 °C trials. Tympanic membrane (T _tym ) temperature was measured in MS (n = 16) and CON (n = 15) groups in the 30 °C condition. A modified fatigue impact scale (MFIS) questionnaire was used to assess subjective measures of psychosocial, physical and cognitive fatigue in the 30 °C condition. Results: Irrespective of ambient temperature, no group differences were observed for T _re (MS: 37.07 ± 0.30 °C; CON: 37.18 ± 0.30 °C; P = 0.29), T _eso (MS: 36.84 ± 0.42 °C; CON: 36.92 ± 0.29 °C; P = 0.36) or resting VO ₂ (MS: 3.89 ± 0.18 ml⋅kg ⁻¹ ⋅min ⁻¹ ; CON: 3.98 ± 0.17 ml⋅kg ⁻¹ ⋅min ⁻¹ ; P = 0.67). Similarly, no group differences were observed for T _tym (MS: 36.52 ± 0.38 °C; CON: 36.61 ± 0.33 °C; P = 0.55) in the 30 °C condition. Resting T _re did not correlate with subjective measures of fatigue: physical: r = -0.11, P = 0.67; cognitive: r = -0.14, P = 0.60; and psychosocial: r = 0.05, P = 0.84. Conclusion: Contrary to recent reports, resting core temperature is not elevated in relapsing-remitting MS patients compared to healthy controls when measured using precision thermometry. Furthermore, no association was observed between resting T _re and any subjective measures of fatigue in a subset of participants with MS.