Health news

Hot weather worsens memory in MS patients

18th February 2011 - After the coldest winter in the UK for 31 years, most of us are pining for summer. However, for many people with multiple sclerosis (MS), hotter temperatures may not be so welcome because they bring worsening symptoms.

MS is the most common neurological condition in young adults in the UK and affects around 85,000 people.

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 Dr James Sumowski, of the Kessler Foundation Research Center in the US.

The study was presented on Thursday at the 63rd annual meeting of the American Academy of Neurology.

MS worse in hot weather

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 Dr Barbara Giesser says the link between hot weather and worsening MS symptoms has been recognised 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 down during warm weather by drinking something cold or sucking on ice.

This study was 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 scrutinise the data prior to publication in a medical journal.