Environmental thermal exposure and disability worsening in multiple sclerosis
Abstract
Background: Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system affecting over 2.9 million people worldwide. It usually progresses from relapses with partially reversible neurological symptoms to long-term disability. Increasing evidence suggests that heat exposure may increase relapse risk, but its role in long‑term disability progression remains unclear. This study assesses the association between meteorological factors and disability worsening in MS.
Methods: We used data from the French CONFISEP-OFSEP cohort, including 1,189 patients with relapsing-remitting MS followed up between 2018 and 2021. Disability progression was assessed using the Expanded Disability Status Scale (EDSS). Outdoor environmental thermal exposures during the 6‑month periods preceding each visit were estimated at the patients’ residential addresses using meteorological data from Météo‑France. Disability worsening (i.e. an increase in EDSS score) was modelled according to environmental thermal exposures using continuous‑time Markov multi-state models.
Results: A total of 3,720 EDSS assessments were conducted, with scores ranging from 0 (no disability) to 7 (severe disability requiring wheelchair use). 402 patients experienced at least one episode of disability worsening. Preliminary analyses suggest that the risk of disability worsening was higher in summer–spring than in winter–autumn for EDSS < 2 (hazard ratio (HR) = 1.60–1.70; 95% CI = 1.09–2.44). Higher minimum temperature was also associated with disability worsening for EDSS < 3 (HR = 1.10–1.12; 95% CI = 1.03–1.25).
Conclusions: With rising global temperatures, heat exposure may increasingly influence MS activity. Identifying modifiable environmental risk factors could inform preventive strategies and improve long‑term patient outcomes.
Funding: This research was supported by IReSP (IReSP-AAP-2023-BLANC-331593) and by Assistance Publique–Hôpitaux de Paris (Fonds d’intéressement à la recherche).
Key messages: • This study provides longitudinal evidence of a link between heat exposure and worsening of disability in people with multiple sclerosis.
• This work supports the development of strategies aimed at preventing the impact of rising temperatures on people with multiple sclerosis.
Related
- Disease-modifying therapies in managing disability worsening in adult relapsing multiple sclerosis: a population-based longitudinal study using the MSBase registry
- Hormone Replacement Therapy and Disability Progression in Women with Multiple Sclerosis
- Apathy-depression overlap: unmasking hidden disability profiles in multiple sclerosis
- Rest-activity and circadian rhythm parameters relate to cognition and disability outcomes in multiple sclerosis
- Association Between Disability and Longitudinal Brain Volumetric Measures Across the Peri-Pregnancy Period in Women with Multiple Sclerosis: A Pilot Study
BibTeX
@article{morlighem2026environmental,
title = {{Environmental thermal exposure and disability worsening in multiple sclerosis}},
author = {C Morlighem and B Chaix and J Hidalgo and N Strzelewicz and J Wurtz and V Masson and E Januel and F Tubach and C Papeix and G Fancello},
journal = {The European Journal of Public Health},
year = {2026},
month = oct,
doi = {10.1093/eurpub/ckag169.341},
url = {https://doi.org/10.1093/eurpub/ckag169.341},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - Environmental thermal exposure and disability worsening in multiple sclerosis
AU - C Morlighem
AU - B Chaix
AU - J Hidalgo
AU - N Strzelewicz
AU - J Wurtz
AU - V Masson
AU - E Januel
AU - F Tubach
AU - C Papeix
AU - G Fancello
PY - 2026
DA - 2026/10/01
JO - The European Journal of Public Health
DO - 10.1093/eurpub/ckag169.341
UR - https://doi.org/10.1093/eurpub/ckag169.341
AB - Background: Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system affecting over 2.9 million people worldwide. It usually progresses from relapses with partially reversible neurological symptoms to long-term disability. Increasing evidence suggests that heat exposure may increase relapse risk, but its role in long‑term disability progression remains unclear. This study assesses the association between meteorological factors and disability worsening in MS. Methods: We used data from the French CONFISEP-OFSEP cohort, including 1,189 patients with relapsing-remitting MS followed up between 2018 and 2021. Disability progression was assessed using the Expanded Disability Status Scale (EDSS). Outdoor environmental thermal exposures during the 6‑month periods preceding each visit were estimated at the patients’ residential addresses using meteorological data from Météo‑France. Disability worsening (i.e. an increase in EDSS score) was modelled according to environmental thermal exposures using continuous‑time Markov multi-state models. Results: A total of 3,720 EDSS assessments were conducted, with scores ranging from 0 (no disability) to 7 (severe disability requiring wheelchair use). 402 patients experienced at least one episode of disability worsening. Preliminary analyses suggest that the risk of disability worsening was higher in summer–spring than in winter–autumn for EDSS < 2 (hazard ratio (HR) = 1.60–1.70; 95% CI = 1.09–2.44). Higher minimum temperature was also associated with disability worsening for EDSS < 3 (HR = 1.10–1.12; 95% CI = 1.03–1.25). Conclusions: With rising global temperatures, heat exposure may increasingly influence MS activity. Identifying modifiable environmental risk factors could inform preventive strategies and improve long‑term patient outcomes. Funding: This research was supported by IReSP (IReSP-AAP-2023-BLANC-331593) and by Assistance Publique–Hôpitaux de Paris (Fonds d’intéressement à la recherche). Key messages: • This study provides longitudinal evidence of a link between heat exposure and worsening of disability in people with multiple sclerosis. • This work supports the development of strategies aimed at preventing the impact of rising temperatures on people with multiple sclerosis.
SN - 1101-1262
SN - 1464-360X
ER -