Unseasonably Warm Weather Linked To MS Symptoms

By Jim Kling


Warm-weather events, even just unseasonably warm spells, may exacerbate multiple sclerosis (MS) symptoms and may lead to more acute care visits, according to an analysis of patients at the Palo Alto (Calif.) Veterans Affairs clinic. The findings could have implications for patient management, especially in the wake of global warming that will make such patterns more frequent.

“I think there’s also a potentially important role here for health care providers to have frank discussions with their MS patients about precautions that they can take when temperatures are warmer than expected,” said Holly Elser, PhD, during a presentation of the study at the 2021 annual meeting of the American Academy of Neurology. Dr. Elser is a medical student at Stanford (Calif.) Medical Center.

The study got its start when Dr. Elser had a patient with MS in for a wellness visit. “She and I were discussing how her symptoms had progressed since her last visit and how she was managing at home. She mentioned offhandedly, ‘you know, my MS gets really bad when it’s hot outside,’ ” said Dr. Elser. She added that heat sensitivity is a well-understood clinical feature of MS, with 80% of patients experiencing heat sensitivity, but there have been few studies on weather and temperature and their impact on the disease.

To Dr. Elser’s surprise, the increase in urgent care visits wasn’t linked to absolute temperature. Rather, visits spiked when there was a high-end deviation from the expected temperature, defined as occurring during a month when the average local temperatures were 1.5° C above the long-term average. “The best [explanation] I can come up with is that patients with MS, especially those who’ve been living with it for a long time, can sort of anticipate that they need to protect themselves when it’s hot outside. But when it’s a little bit warmer than you’re expecting, perhaps there’s some behavioral component where you walk outside in the winter wearing too many layers and then walk into a heated storefront, and you get really, really hot all of a sudden. So I think that there is potentially a behavioral mechanism where you just expect the weather to be a little bit cooler than it actually is. Another explanation, which is sort of theorized in the literature on temperature and violence, is that perhaps we actually habituate to certain temperatures during certain seasons based on where we live, and the deviation in and of itself is enough to sort of trigger physiological and behavioral changes,” said Dr. Elser.

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Research that sheds light on the impact of rising temperatures on MS patients’ use of health care services is critical because it can inform anticipatory guidance we give to patients.
The study was a welcome addition to the literature, according to Altaf Saadi, MD, who moderated the session. “Research that sheds light on the impact of rising temperatures on MS patients’ use of health care services is critical because it can inform anticipatory guidance we give to patients. It can also inform conversations we have with policy makers about climate change so we can turn research like this into policies to help the most patients possible,” Dr. Saadi said in an interview. She is a general neurologist and health services researcher at Massachusetts General Hospital and instructor of neurology at Harvard Medical School, both in Boston.

The researchers analyzed data from 75,395,334 individuals, 106,225 with MS, age 18-64, who were followed between 2003 and 2017. Dr. Elser presented the results graphically, both overall and for men and women individually. The findings were similar between men and women, and the strongest effects of weather were associated with visits among individuals aged 56-64 years. “This may be a function of the accrual of disability related to MS over time as the disease progresses, or the accrual of comorbidities, or some combination,” said Dr. Elser. “In general, our results underscore a point that has been made previously in the literature, which is that it’s important to recognize that some individuals may be uniquely susceptible to changes in weather [or] climate based on preexisting conditions.”

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The study was limited by having no direct measure of MS symptoms or disease burden, relying on health care visits as a proxy.

The study received funding from the National Institutes of Environmental Health Sciences, the National Institutes on Drug Abuse, and Stanford University. Dr. Elser and Dr. Saadi have no relevant financial disclosures.