Multiple Sclerosis Prevalence Increasing Faster Among Women Than Men

Caroline Cassels

http://www.medscape.com/viewarticle/555620

April 24, 2007 — Over time, more women than men are developing multiple sclerosis (MS), new research has shown.

In a study that will be presented May 2 at the American Academy of Neurology's 59th Annual Meeting, investigators at the University of Alabama at Birmingham School of Public Health, Cleveland Clinic, in Ohio, and Barrow Neurological Institute, in Phoenix, Arizona, found that between 1940 and 2000, the ratio of MS in women compared with men increased by approximately 50% per decade.
In 1940, the ratio of women to men with MS was 2 to 1. In 2000 it was 4 to 1, a finding that principal investigator Gary Cutter, PhD, from the University of Alabama School of Public Health, says confirms similar results from a recent Canadian study.

Published in 2006 in Lancet Neurology (Orton SM et al. Lancet Neurol. 2006;5: 932 – 936), the study found that among individuals born during the 1930s, the ratio of women to men who developed MS in Canada was 2 to 1. However, the study showed that among those born during the 1980s, this ratio increased to over 3 to 1.

Similar findings, he said, were reported by Norwegian researchers in the European Journal of Neurology in 2001 (Celius EG, Vandvik B. Eur J Neurol. 2001;8:463 – 469).

"If this were the first time this [finding] had been observed, I would be very, very cautious about suggesting it is real. But given the fact that other investigators have made the same observation, I am pretty comfortable that this is a valid phenomenon. Having said that, we have no insight [from this study] as to why it is occurring," Dr. Cutter told Medscape.

Enormous Increase

Investigators examined data from the North American Research Committee on Multiple Sclerosis (NARCOMS) database. This online MS patient registry is one of the largest of its kind and includes 32,414 individuals with MS from across the United States and Canada.

Individuals enrolled in the registry self-report demographic and clinical information regarding their disease at enrollment and semiannually thereafter.

Age, sex, age at diagnosis, and age at onset were used to assess the female-to-male ratio. Investigators then adjusted for age at disease onset and year of diagnosis. Of the total number of registry participants, 30,336 were included in the final analysis.

Of the total study group, 72.5% were females and 93% were white. The overall average year of diagnosis was 1988 for males and 1992 for females. Investigators found that the ratio of females to males increased from 2 to 1 for subjects diagnosed in the earlier time periods to more than 4 to 1 in recent years, an enormous increase in women over a 60-year period.

In addition, he said, the changes in prevalence appear to be more pronounced among those diagnosed at younger ages and in young women.

Avenues of Investigation

This research, along with the previous studies conducted in Canada and Europe, may help direct future studies.

"These studies show there are changes in the occurrence of MS among females relative to males, which should provide us with potential clues and possible avenues of investigation. We need to consider the changes that have occurred over time among women that may give rise to the disease. This could provide us with an important area of research that, to date, either has not been considered or has been understudied, leading ultimately to ways of preventing the disease," said Dr. Cutter.

Possible candidates include the increased use of hair dye and cosmetics, which may block vitamin D absorption, a factor some are considering associated with MS, the use of oral contraceptives, changes in obesity and smoking rates, earlier menstruation, and later age of first births.

American Academy of Neurology 59th Annual Meeting: Abstract P04.068. April 28 – May 5, 2007