As average temperatures around the globe climb, a study has found people with multiple sclerosis may expect worsening symptoms, enough to send them to the hospital more often. The study 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 degrees Celsius, or almost 2 degrees Fahrenheit.

For the study, researchers at the Stanford University School of Medicine in Stanford, Calif., 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 percent increased chance of having an emergency department visit compared to periods of normal weather. Participants had a 3 percent increased chance of having an inpatient visit and a 1 percent 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.

Limitations of the study include that the study was retrospective and researchers had no direct way to measure peoples’ symptoms.

The study will be presented at the American Academy of Neurology's 73rd Annual Meeting.