Can Rising Global Temperatures Worsen MS Symptoms?

In a conversation with a patient living with multiple sclerosis (MS), Holly Elser, PhD, learned heat was especially triggering for the patient’s MS symptoms. When she arrived home that evening, Elser, a fourth-year medical student at Stanford with a PhD in epidemiology, dug deeper into the research on heat and MS.

Despite a relatively robust set of research on how sudden changes in core body temperature can cause a temporary worsening of neurological symptoms, she discovered a lack of information on how weather plays a role.

“There was very little on the implications of weather and temperature for individuals living with multiple sclerosis, despite the fact that we know clinically that heat is a major trigger,” Elser says.

To better understand the connection, Elser and her research team studied the links between abnormally warm weather and hospital visits for more than 100,000 people with MS. They found in months that were warmer than usual, there was an increase in the number of people receiving emergency or inpatient care for MS symptoms. The preliminary research will be published shortly and will be presented at the American Academy of Neurology’s Annual Meeting next month.

Rising Temperatures and MS Symptoms

People with MS often experience worsening symptoms with an increase in body temperature. The autoimmune disorder attacks myelin—the sheath that protects nerve cells and ensures signals are quickly passed between them. Signals may be able to travel through the nervous system even with low levels of myelin. But under some conditions, like a spike in body temperature, nerve impulses are blocked.

Nancy Sicotte, MD, chair of the department of neurology and director of the multiple sclerosis program at Cedars-Sinai in California, says that for MS patients who are particularly heat-sensitive, things like heavy aerobic exercise and fighting off infection can cause the reemergence of symptoms that seemed to be resolved.

“It’s confusing for patients when they’re first diagnosed to understand that doesn’t mean they’re having a new attack—it’s not a new inflammatory event,” Sicotte says. “But it’s a sign that they had damage to their nervous system, and they’ve had some recovery but not complete.”

Climate Change’s Impact

The research team studied months where the temperature was unusually high for that time of year—specifically when regional temperatures were higher than the long-term average for that month by nearly 2 degrees or more. In doing so, they could track the effects of increased temperature year-round, rather than only during periods of extreme heat.

“The fact that we still see effects of these more subtle variations in temperature points to the fact that there’s probably some unobserved or unrecognized consequences of changing climates that aren’t necessarily related to the more obvious and highly publicized extreme weather and temperature events, especially to people we know to be vulnerable,” Elser says.

Nine of the ten warmest years on record have occurred since 2005, according to the National Oceanic and Atmospheric Administration. Over the next century, the Intergovernmental Panel on Climate Change projects that global temperature will rise by more than 2.5 degrees, and possibly by more than 3.5 degrees.

“I don’t think it’s surprising,” Sicotte says. “We definitely see people suffering more when the weather gets hotter.”

Establishing a Trend

To study this link, the research team used a large database of insurance claims from more than 7.5 million people between 2003 to 2017. They identified more than 100,000 people with MS and created a database to track whether an individual who was eligible for insurance visited the hospital or required emergency services for their MS each month.

“These population-based studies are helpful in actually identifying trends that would be hard to see,” Sicotte says.

Such a large-scale retrospective study can indicate a link between temperature and MS symptoms. But Elser says the data really only captures the subset of patients with serious symptoms. People with MS who experience symptoms but do not seek treatment were likely missed in this study.

“Work like ours is meaningful because it establishes a trend in a large group of people over a long period of time across the U.S., but it really motivates reexamination of this phenomenon in datasets where more precise measures of symptoms and disability are available,” Elser says.

For a more detailed picture of the effect of anomalies in temperature on MS patients, future studies may track the symptoms of a smaller set of individuals over a long period of time.

“I hope what we will continue to learn is that it’s not just the extremes of temperature that matter—that there may be more minor variations in temperature that are potentially bothersome and harmful to individuals with MS,” Elser says.

How to Support MS Patients

Healthcare providers often recommend people with MS prepare for excess heat when they go outside or exercise. They might, for example, check the weather before leaving home so they don’t overdress and overheat, bring cold water to drink, or wear cooling scarves or vests.

“We see patients who maybe grew up in Minnesota or something and they live [in Southern California] but then they go home for Christmas and they find that they feel so much better when they’re in cold weather,” Sicotte says.

Elser says it’s important to ensure people gain equitable access to cooling resources such as electrical vouchers to pay for air conditioning and access to cooling stations.

“Some of it is just sort of reiterating the things that we already know to be effective and some of it is thinking about which patients are most vulnerable because they have less access to the types of resources that they would need to be able to utilize to protect themselves,” Elser says.