Researchers at the Kessler Foundation found that patients with MS performed 70% better on tests involving thinking, or cognitive functioning, on cooler days than they did at warmer times of the year.
"These findings are important because in many cases, cognitive changes take a greater psychological toll on MS patients than changes in motor symptoms do," said the study's lead author, Victoria Leavitt, a neuropsychologist and post-doctoral fellow at the Kessler Foundation Research Center.
"People who have MS often leave the workforce before their motor symptoms emerge, and the reason they'll often give is fatigue," said Leavitt. "But it's possible that it may be related to these changes in cognition, which are requiring them to use their brains in a different way."
MS patients respond better when it's cooler
For the study, 40 people with MS and 40 without the nervous system disease took the same cognitive tests at different times throughout the calendar year. The researchers recorded the temperature on each day that the patients were tested. While the MS patients performed better on these tests on cooler days, there was no difference in the test results of the healthy controls.
The reason why temperature changes might affect MS patients' thinking isn't known, but Leavitt said one possible explanation is that the underlying mechanisms that regulate the body's reaction to heat may work less effectively in people with MS.
Leavitt said her work was a direct result of a 2010 study by scientists at Brigham and Women's Hospital in Boston, which showed that brain lesion activity in MS patients was two to three times higher during the months of March through August, compared with other times of the year. That paper was published in the journal Neurology.
Another MS researcher called Leavitt's study "an important follow-up" to the paper by Brigham and Women's researchers.
"It's a fairly recognised phenomenon that MS patients complain of increased symptoms in the summer months, but this is the first time that someone has really looked at cognitive functioning related to temperature," said Dr Jonathan L. Carter, associate professor of neurology at the Mayo Clinic College of Medicine.
Findings could influence life decisions
The next steps, said Carter, "may be to find out if these changes are related to new disease activity or just worsening deficits related to the existing lesions, and also look at whether existing drug therapies might help with this temperature-related cognitive impairment."
"One really important bottom-line implication of our findings is for researchers who are performing drug trials," Leavitt added. "They need to consider this temperature effect when they're doing baseline cognitive testing. The results could be very different if you take your baseline in summer or winter," she said.
Depending on the results of future research, it's also conceivable that the findings could influence life decisions made by people with MS, the researchers say.
Experts note that research presented at meetings has not been subjected to the same type of rigorous scrutiny given to research published in peer-reviewed medical journals.