AAN: Gender Gap Widens for Multiple Sclerosis

BOSTON, April 30 -- The gender gap in multiple sclerosis in the United States has doubled over the past six decades, investigators reported here.

In 1940 the female-to-male ratio of multiple sclerosis was about two to one, but it had grown to about four to one by the year 2000, reported Gary Cutter, Ph.D., of the University of Alabama at Birmingham School of Public Health, and colleagues, at the American Academy of Neurology meeting.

"That's an increase in the ratio of women to men of nearly 50% per decade," said Dr. Cutter. "We don't yet know why more women are developing MS than men."

The widening gender gap could be related to changes in lifestyle and medical choices over the decades, the investigators speculated. These changes include the advent of oral contraceptives, younger age at menarche, climbing obesity rates, changes in smoking habits, and later maternal age at first birth.

To determine prevalence changes, the researchers conducted a search of the North American Research Committee On Multiple Sclerosis registry, which is hosted at the Barrow Neurological Institute in Phoenix.

The database contains self-reported demographic and clinical information regarding MS at enrollment and at semi-annual intervals. The investigators extracted data on patient age, gender, age at diagnosis and age at symptom onset to estimate the female-to-male ratio in the year diagnosed, adjusted for age at diagnosis.

They examined records on 30,336 MS patients, 72.5% of whom were women, and approximately 93% of whom were white. The mean year of diagnosis was 1973 for men and 1975 for women.

"The increase in the odds of being an MS female was 1.046 per year (95% confidence interval, 1.043-1.049), or slightly less than a 50% increase in the ratio per decade," the authors wrote. "This ratio has increased for all age groups with a larger increase for younger ages at onset."

Dr. Cutter and colleagues were prompted to look at the gender ratio in MS by the results of a Canadian study published in the November 2006 issue of Lancet Neurology. The authors of that study had found that the female-to-male MS ratio had increased from about 1.9-to-1 in 1931 to about 3.2-to-1 in 1980.

"This rapid change must have environmental origins even if it is associated with a gene-environment interaction, and implies that a large proportion of multiple sclerosis cases may be preventable in situ," wrote the members of the Canadian Collaborative Study Group.

The Alabama researchers' findings, which confirm those of their Canadian colleagues, and also point to changes in demographic patterns and lifestyle choices over the intervening decades as possible clues to the etiology of MS, they wrote.

"We also need to ask general questions about what women do differently than men, such as use of hair dye and use of cosmetics that may block vitamin D absorption," he said. "At this point we're just speculating on avenues of research that could be pursued."