Hot Weather Worsens Memory in MS Patients
New Research Shows That Thinking Skills Are Better for MS Patients on Colder Days
By Salynn Boyles
WebMD Health News
Reviewed by Laura J. Martin, MD
woman soaking in the sun

Feb. 17, 2011 -- As one of the most brutally cold winters on record drags on, most of us are pining for summer. But for many patients with multiple sclerosis, hotter temperatures may not be so welcome because they bring worsening symptoms.

Now new research finds this may be especially true for some of the least well understood symptoms of the disease -- thinking and memory problems.

When researchers tested the memories and information processing abilities of MS patients and people without the disease at different points during the year, they found that the MS patients performed worse on the cognitive tests in warmer seasons.

No seasonal difference was seen in test performance among people without multiple sclerosis.

The study is the first to document the impact of hotter temperatures on memory and thinking function in MS patients, say neuropsychologist and study co-author James F. Sumowski, PhD, of the Kessler Foundation Research Center in West Orange, N.J.

The study will be presented in April at the 63rd annual meeting of the American Academy of Neurology in Honolulu.

A Visual Guide to Multiple Sclerosis
MS Worse in Hot Weather

Each week in the United States about 200 people are diagnosed with MS, according to the National MS Society.

Numbness, limb weakness, and problems with balance and vision are among the most widely known symptoms of the disease, but problems with thinking and memory are also very common.

Neurologist Barbara Giesser, MD, says the link between hot weather and worsening MS symptoms has been recognized for more than 100 years.

“At the turn of the 20th century, long before we had MRIs and fancy diagnostics, one way of diagnosing MS was the ‘hot bath’ test,” she says. “They would put the patient in a tub of very hot water and if their symptoms worsened, the diagnosis was confirmed.”

Although not all MS patients have worse symptoms in hot weather, Giesser says the vast majority have some degree of heat sensitivity.

The newly reported study included 40 MS patients and 40 people without the disease matched to the patients for age, sex, and education level.

All the participants underwent tests designed to measure memory function and information acquisition and processing.

Overall, the MS patients performed 70% better on the thinking tests when the tests were given in colder months compared to warmer ones.

The researchers did not measure the patients’ body temperatures or record how long they spent outside before taking the tests.
MS Lesions More Common in Summer

It is not clear if hot weather affects the progression of MS or just causes temporary worsening of symptoms.

A brain imaging study published last summer by researchers at Harvard University showed that MS-associated brain lesions actually occur more often in warmer months than in colder ones.

Heat appears to slow down nerve impulses that are already impaired by the disease, Giesser says.

“Basically nerves are electrical cables,” she says. “MS damages the insulation and short circuits the nerves so that they don’t conduct signals as efficiently. If you heat up a damaged nerve, that causes further problems.”

Giesser recommends her heat-sensitive patients try cooling strategies like drinking something cold or sucking on ice during warm weather.

This study will be presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.