When the weather is unusually warm, people with multiple sclerosis (MS) are more likely to require emergency medical care, new research shows.
The findings indicate that people with health conditions like MS may be at increased risk of health problems as temperatures rise due to climate change, according to Holly Elser, PhD, an epidemiologist and medical student at Stanford University.
Elser presented the findings at the annual meeting of the American Academy of Neurology in a talk titled, “Anomalously warm weather and acute care visits in patients with multiple sclerosis: A retrospective study of privately insured individuals in the U.S.“
The idea for this study, according to Elser, originated with a MS patient during a routine medical appointment: “[the patient] mentioned off-handedly, ‘you know, my MS gets really bad when it’s hot outside,'” said Elser.
This prompted Elser and colleagues to wonder how people with MS will be affected as human-driven climate change causes global temperatures to increase.
Reviewing the published literature, the scientists found that for some conditions — like dementia and heart/lung diseases — the effects of rising global temperatures have been well-documented. However, this was not the case for MS, even though as many as four in five MS patients experience abnormal sensitivity to heat as a symptom of the disease.
“There was actually very little literature on the implications of weather and temperature for individuals with MS, who are almost certainly affected by the extremes of heat, but may also experience symptoms in response to more subtle seasonal variations in temperature. Ultimately, this is what motivated our study,” Elser said.
Elser and colleagues analyzed a large private insurance database in the U.S. to look for associations between abnormally warm weather and MS patients going to the hospital. In total, the researchers assessed data for 106,225 MS patients with follow-up from 2003 to 2017. The majority (59%) were women ages 36 to 55.
Abnormally warm weather was determined using publicly-available temperature data. For the purposes of their analysis, the researchers defined “abnormally warm” as temperatures that were at least 1.5 C higher than the long-term average temperature for that month in a given place.
“This threshold was selected both to be consistent with previous literature on the health effects of temperature, but also to be consistent with efforts to limit the rise in global temperature by 1.5 C as described in the Paris Agreement,” Elser said.
“I think it’s important to note that our measure of anomalously warm weather isn’t limited to temperature extremes that we’d typically observe in the summer and early autumn, but instead may capture these more indolent increases in regional temperature that can occur year-round, even in the winter,” Elser added.
Based on statistical models, the researchers determined that people with MS were about 4% more likely to go to the emergency room when temperatures were abnormally high. Also, inpatient hospital visits (when a person needs to stay at the hospital) were 3% more common when temperatures were high.
Both of these increases were statistically significant — meaning that, mathematically, it is extremely unlikely that the difference is random.
The effects of warmer weather were similar among women and men, and they were particularly strong among older individuals.
“The strongest and most precise associations [between warm weather and emergency/inpatient visits] were detected among individuals ages 56 to 64 years old,” Elser said.
According to Elser, this could be because of increased disability as MS progresses over time, or it could be due to the accrual of comorbidities (existing health conditions other than MS), or some combination of these and other factors.
“In general, our results underscore a point that’s 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 and climate based on pre-existing conditions,” Elser concluded.
“I think there’s also a potentially important role here for healthcare providers to have frank discussions with their MS patients about precautions that they can take when temperatures are warmer than expected,” Elser added.
Elser noted that, because of the insurance database used for the analysis, detailed information about MS severity and symptoms was not available, and neither were individual sociodemographic data. These were limitations of the analysis, according to Elser.
“This is only one study, but I think our findings naturally motivate ongoing research in this area,” Elser said.
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