Rising average temperatures may lead to a worsening of symptoms in people with multiple sclerosis (MS) and a greater need for hospital care, according to a preliminary study by researchers in the U.S.
Its findings will be presented at the virtual annual meeting of the American Academy of Neurology, set for April 17 to 22.
“Our study suggests that warming trends could have serious health implications over the long term for people living with MS,” Holly Elser, PhD, an epidemiologist at Stanford University School of Medicine in California and a study author, said in a press release.
Many people with MS experience a temporary worsening of symptoms, such as fatigue or weakness, when they overheat in hot weather. These changes are linked to heat sensitivity, and can result from slight increases in core body temperature that further affect the ability of nerves to conduct electrical impulses, especially if the nerve fibers are damaged as happens in MS.
The expectation that “periods of anomalously warm weather will become more frequent with climate change” was the basis for this preliminary study, Elser said.
The association between unusually warm weather and greater medical needs was based on evaluations of insurance claims filed by 106,225 individuals with MS in the United States. Unusually warm weather was defined as any month in which local average temperatures were higher by at least 1.5 degrees Celsius (almost 2 degrees Fahrenheit) than that area’s long-term average temperature.
Claims analyzed covered these patients’ emergency hospital visits, and inpatient and outpatient medical visits during months spotted as unusually warm. The number of these claims were then compared to the number of similar claims these same people filed during periods of normal weather to calculate the estimated effect of rising temperatures.
These estimates associated warmer-than-normal months with at least 592 more hospital emergency department visits, 1,260 more inpatient visits, and 1,960 more outpatient visits relative to other months.
The probability, or risk, of greater healthcare utilization during months of unusually high temperatures, likewise, was a 4% rise for emergency room visits, 3% for inpatient visits, and 1% for outpatient visits, again compared to normal weather months.
“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.
Since the study was retrospective — meaning, conducted based on existing data — researchers were unable to assess symptoms directly and show an association between symptoms and weather.
This work was supported by two branches of the National Institutes of Health, the National Institute of Environmental Health Sciences and the National Institute on Drug Abuse.
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