Study Investigates Link Between Multiple Sclerosis, Warmer Weather

Preliminary study results point to a possible connection between increasing global temperatures and an increased risk of hospitalization during the course of multiple sclerosis (MS), according to an abstract that will be presented at this year’s American Academy of Neurology (AAN) 73rd Annual Meeting in April.

This greater risk stems from possible worsening symptoms, the authors noted. They compared visits for each patient during anomalously warm and normal weather periods. Their primary outcome of this retrospective cohort study was annualized warm weather–related risk of out/inpatient and emergency department visits in the United States, and they defined anomalously warm weather as “any month in which local average temperatures were higher than the long-term average temperature for that month by at least 1.5°C, or almost 2°F.”

“We know that heat sensitivity is common in multiple sclerosis, and climate scientists expect that periods of anomalously warm weather will become more frequent with climate change,” lead study author Holly Elser, PhD, of Stanford University School of Medicine and a member of the AAN, said in a statement. “Our study suggests that warming trends could have serious health implications over the long term for people living with MS.”

Of the 75 million-plus patients identified from a nationwide patient-level commercial and Medicare Advantage claims database, 106,225 (0.14%) had MS (59.0% aged 36-55 years; 76.6% women). Among these patients, the risk of emergency department visits rose the most, at 4%, compared with 3% for inpatient visits and 1% for outpatient visits.

The follow-up period had opposite results. There was an increase of 1960 outpatient and 592 emergency department visits during anomalously warm weather. Inpatient visits remained in the middle, at 1260 more visits.

Overall, although results were similar between men and women, older individuals had the strongest correlation—with results among this group varying by region and season.

“As global temperatures rise, individuals with MS may represent a sub-population uniquely susceptible to associated periods of anomalously warm weather,” the authors concluded, “with implications for both health care providers and systems.”

They emphasized that despite these increases appearing small, “the associated absolute effect on people with MS and the health care system is meaningful,” Elser stated.

All individuals included in the final analysis had at least 3 MS-related in/outpatient or disease-modifying therapy claims in a 365-day period.

The study’s retrospective design and not being able to directly measure symptoms were noted at limitations to these findings. Further study is warranted.

Reference

Elser H, Parks R, Moghaven N, et al. Anomalously warm weather and acute care visits in patients with multiple sclerosis: a retrospective study of privately insured individuals in the US. Presented at: the American Academy of Neurology's 73rd Annual Meeting; April 17-22, 2021. Accessed March 5, 2021. https://bit.ly/3eeOC18