As average temperatures around the globe climb, a preliminary study has found people with multiple sclerosis (MS) may expect worsening symptoms, enough to send them to the hospital more often. The preliminary study released today, March 2, 2021, will be presented at the American Academy of Neurology's 73rd Annual Meeting being held virtually April 17 to April 22, 2021.

"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," said study author Holly Elser, PhD, of Stanford University School of Medicine in Stanford, Calif., and a member of the American Academy of Neurology. "Our study suggests that warming trends could have serious health implications over the long term for people living with MS."

Anomalously warm weather was defined as any month in which local average temperatures were higher than the long-term average temperature for that month by at least 1.5 degrees Celsius, or almost 2 degrees Fahrenheit.

For the study, researchers looked at insurance claims for 106,225 people with MS living across the United States. Researchers calculated the estimated effect of anomalously warm weather on MS-related emergency department, inpatient and outpatient visits. Researchers then compared the number of medical visits for each person during periods of anomalously warm weather to periods of normal weather.

Researchers found that during periods of anomalously warm weather, participants had a 4% increased chance of having an emergency department visit compared to periods of normal weather. Participants had a 3% increased chance of having an inpatient visit and a 1% increased chance of having an outpatient visit during anomalously warm periods compared to periods of normal weather.

Researchers estimate that over the course of follow-up, periods of anomalously warm weather were associated with an estimated excess of at least 592 emergency department visits, 1,260 inpatient visits and 1,960 outpatient visits related to MS.

"While the relative increase in risk of visits is small, the associated absolute effect on people with MS and the health care system is meaningful," Elser said.