February 18, 2011 — People with multiple sclerosis (MS) may find it harder to think clearly and remember things on warmer days of the year, according to a new study.
The study was released February 17 ahead of presentation in April at the American Academy of Neurology 63rd Annual Meeting in Honolulu, Hawaii.
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| Dr. Victoria Leavitt |
Victoria M. Leavitt, PhD, postdoctoral fellow in the Neuropsychology & Neuroscience Laboratory, Kessler Foundation Research Center, in West Orange, New Jersey, said she hopes the study will generate increased awareness of the potential impact of warmer temperatures on cognitive function in patients with MS.
"Surprisingly, the factor that is most attributed by persons with MS for leaving the workplace is not motor symptoms, as one might expect, but in fact cognitive factors," Dr. Leavitt told Medscape Medical News. "A nebulous sense of 'not being on top of things' or not being able to handle things the way they used to is frequently described by persons with MS."
Patients with MS, she added, will benefit from the knowledge that their cognitive abilities may fluctuate according to outdoor temperature. "Someone who has to schedule a very important test or has a job-related challenge on the horizon may do well to plan around the more difficult months," she suggested.
Better Cognitive Performance on Cooler Days
The new findings build on results of prior studies that have shown a seasonal pattern to MS activity.
Among them, a study from Boston, Massachusetts, published last year showed increased T2 lesion activity on brain magnetic resonance imaging (MRI) during the warmer months of the year in patients with MS (Neurology. 2010;75:799-806). A study from Germany found an increase in gadolinium-enhancing lesions in the spring and early summer in a group of MS patients (Ann Neurol. 2000;47:276-277).
The current study, the researchers say, is first to suggest a possible link between warm weather and cognitive function in patients with the disease.
Over about a year, Dr. Leavitt and colleagues enrolled 40 patients with MS and 40 healthy people without MS in their study. All subjects completed neuropsychological tests measuring cognitive status (processing speed, learning, and memory), and patients with MS also underwent high-resolution MRIs of the brain to measure brain atrophy, which the researchers controlled for.
The researchers recorded the daily outdoor temperature for each test day. The lowest temperature was 12°F, and the highest was 82°F, "so there was a nice range," James F. Sumowski, PhD, who worked on the study, noted in an email. Across the whole study, the average temperature was 55°F.
...there was an astounding association between temperature and cognitive performance, such that on cooler days persons performed fully 70% better.
"Taking into account the outdoor temperature for the day a research subject was tested, there was an astounding association between temperature and cognitive performance, such that on cooler days persons performed fully 70% better," Dr. Leavitt said. In contrast, healthy controls showed no association between cognitive status and temperature, suggesting that the association between temperature and cognition is specific to MS, the researchers say.
"It's important to note that we do not think transient changes in temperature impact this relationship," Dr. Leavitt said. "We are not recommending people buy industrial strength air conditioners or move to Alaska. It appears that this effect has to do with more stable temperature factors (ie, outdoor temperature)."
Many Questions Remain
Anne Cross, MD, from the Washington University School of Medicine in St. Louis, Missouri, who was not involved in the study, pointed out that what's not clear from the study is whether the outside temperature related to the subjects' core body temperatures.
In an interview with Medscape Medical News, Dr. Cross noted that when the core body temperature of MS patients goes up, it often affects their neurologic functioning; "for example, a fever in a patient with MS may often bring out neurologic symptoms and signs. I'm wondering if a similar phenomenon could be happening in subjects in this study, but it's not clear." Body temperature was not measured in study subjects.
Clearly, more study is needed. Dr. Leavitt said if the link between daily outdoor temperature and reduced cognitive functioning is replicated in other studies, this could have important implications for research studies.
"Many drugs are being developed to target the cognitive symptoms of MS. If a 6-month trial is begun in December and ended in June, one could easily imagine that any hoped for effect of the drug would be washed out by the temperature effect. This is crucial for researchers to consider," Dr. Leavitt said.
American Academy of Neurology (AAN) 63rd Annual Meeting: Abstract 1778. Released February 17, 2011.
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