MS Hospital Visits Increase in Warmer Weather 

April 15, 2021

Individuals with multiple sclerosis (MS) seek additional acute medical care during periods of unusually warm weather, a new study has found, raising concerns about possible increased symptoms and healthcare usage over the long-term because of global warming.

"Our study suggests that warming trends could have serious implications over the long term for people living with MS, and for their healthcare providers," said study author Holly Elser, PhD, MPH, Stanford University School of Medicine, Stanford, California.

The study results were released ahead of their presentation at the American Academy of Neurology (AAN) 2021 Annual Meeting being held virtually April 17-22.

"Anomalously Warm Weather"

Elser told Medscape Medical News that the study was inspired by an patient with MS who mentioned how she typically felt worse during periods of hot weather.

"Heat sensitivity — as described by this patient — is actually a well-recognized clinical feature of this disease. For many individuals with MS, sudden increases in core body temperature can lead to worsening of neurological symptoms," she noted.

"We know that average temperatures are steadily rising worldwide, and climate scientists anticipate that weather and temperature patterns will become variable over time," Elser said. "The adverse effects of rising global temperatures have been documented in the general population, but also for particularly susceptible groups like individuals with preexisting cardiopulmonary disease, dementia, or serious mental illness. But when we looked, there was very little literature on the implications of weather and temperature for individuals with MS." 

For the study, researchers examined commercial and Medicare insurance claims for 106,225 patients with MS aged 18-64 across the United States. They calculated the number of medical visits for each person during periods of anomalously warm weather (defined as any month in which local average temperatures were higher than the long-term average temperature for that month by at least 1.5° C, or almost 2° F) and compared this to the number of visits during periods of normal weather.

Results showed that during periods of anomalously warm weather, participants had a 4% increased chance of having an emergency department visit compared with periods of normal weather (relative risk [RR] 1.04, 95% CI, 1.03 - 1.06), and a 3% increased chance of having an inpatient visit (RR, 1.03, 95% CI, 1.01 - 1.05). In addition, there was a 1% increase in outpatient visits.

While the relative increase in risk of visits is small, the authors believe the results are meaningful, pointing out that on the absolute scale this translates to an estimated excess of at least 592 emergency department visits, 1260 inpatient visits, and 1960 outpatient visits related to MS over the 15-year course of the study associated with periods of anomalously warm weather.

"In other words, modest associations on the relative scale translate into substantial effects on the absolute scale when large populations are exposed (as is the case with weather and temperature), leading to meaningful impacts on patients with MS and the healthcare system," Elser commented. 

She pointed out that the magnitude of effects seen in this study is fairly consistent with other population studies of environmental exposures.

"Overall, our results suggest that periods of anomalously warm weather may precipitate treatment-seeking in the acute care setting among individuals living with MS," Elser stated.

She also noted that the measure of anomalously warm weather used in the study was not limited to extreme temperatures, as it also captured more indolent increases in regional temperatures that can occur year-round.  "This suggests that less extreme increases in local temperatures may be consequential for the health of individuals with preexisting conditions like MS," she said. 

Elser suggested that healthcare providers could have conversations with their patients with MS about taking precautions when temperatures are warmer than expected to protect themselves from any adverse effects.

"This could include keeping a symptom diary to ascertain whether warmer weather leads to worsening of symptoms, strategies such as wearing loose-fitting clothing or wearing layers to avoid overheating if temperatures are warmer-than-expected, or efforts to moderate warmer temperatures by using fans or air conditioning when needed," she commented.

She also raised the possibility that improved energy efficiency and "weatherization" of residences may represent a cost-effective solution with significant health benefits. "Energy vouchers for lower-income individuals living with MS, while a less-viable short-term solution, could potentially be used encourage use during seasons when warm weather events appear to pose the greatest risk," she added. 

Elser noted that limitations of the analysis include no direct measures of MS-related symptoms or disability as well as a lack of individual-level measures of socioeconomic status (such as occupational status, household income, access to air conditioning, housing quality, and race/ethnicity).

"Factors such as these may be key modifiers of the impact of weather and temperature on individuals with MS," she said. "Given these limitations, future research regarding the implications of weather and climate for individuals with MS, especially where direct measures of disease burden and symptoms and other key individual-level data are available, is needed."

Asked how these results relate to the observations that MS is more common in northernmost (colder) latitudes, Elser said the current study focused on hospital encounters among individuals already diagnosed with MS, rather than MS incidence.

But she pointed out that secondary results showed heterogeneity in the association between anomalously warm weather and MS-related healthcare encounters by season and region. By region, the strongest associations were seen in the southern United States; by season the strongest associations occurred in the winter; and by climate zone consistently stronger associations were observed in very cold climate zones and in humid climate zones.

"We anticipate that the seasonal findings could be behaviorally mediated. For example, individuals may be more likely to overheat in the winter if they dress expecting colder temperatures," Elser commented.

"But these observations raise the interesting question as to whether the implications of weather and temperature differ based on geography, and motivates re-examination of this issue in varied study settings,” she added.

Commenting for Medscape Medical News, Lily Henson, MD, specialist and CEO of Piedmont Henry Hospital, Stockbridge, Georgia, said the study may help prepare patients with MS for the potential implications of global warming.

"For example, we should ask patients if they have fans or air conditioning, and advise on staying adequately hydrated during these warmer periods," she noted.

The study was supported by the National Institute of Environmental Health Sciences and the National Institute on Drug Abuse.

American Academy of Neurology (AAN) 2021 Annual Meeting: To be presented April 17-22, 2021.

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