Apr 27, 2007
Is Multiple Sclerosis Increasing among Women Compared to Men?
Press reports are focusing on a study suggesting that over the last few decades a higher proportion of women compared to men have been diagnosed with MS in the U.S. The study, based on an evaluation of participants enrolled in the voluntary patient registry called NARCOMS, is being presented at the American Academy of Neurology’s annual meeting in Boston next week by Dr. Gary Cutter (University of Alabama, Birmingham) and colleagues.
Multiple sclerosis is thought to be autoimmune in nature, and like many other such diseases, develops in women more often than in men; current estimates of the sex ratio suggest that women are two to three times more likely to develop MS than men. Whether women have always been more likely to develop MS, or whether this is a relatively recent phenomenon, has been an open question.
In this study, investigators assessed the sex ratio according to age at onset and year of diagnosis, in 30,336 registered participants of NARCOMS (North American Research Committee on Multiple Sclerosis). They found that among patients diagnosed prior to 1940 who had voluntarily registered with NARCOMS, the ratio of women to men in the U.S. was approximately 2 to 1, and by 2000, the ratio had grown to approximately 4 to 1.
Researchers using a Canada-wide database recently reported that the number of women diagnosed with MS had approximately tripled over the past 60 years (Lancet Neurology 2006 Nov;5(11):932-6). According to the long-term Danish Multiple Sclerosis Registry, which is estimated to capture data on about 90% of the MS population in Denmark, the sex ratio was approximately 1 to 1 in the 1950s, but that there was an increase in incidence among women compared to men starting in the 1970s.
Determining the precise sex ratio and whether it is changing over time is difficult for several reasons. One reason is that in the 1940s and 1950s, medical literature suggests that women were less likely to be properly diagnosed with MS than men. Moreover, since women have a longer life expectancy than men, retrospective studies such as the one using NARCOMS may include an excess of women in the older age groups (e.g., those diagnosed many years ago) due to men having died off in greater numbers. In addition, improvements in diagnostic methods make it difficult to compare the numbers diagnosed today with those diagnosed decades ago, especially if diagnostic methods were differentially applied to women vs. men.
Further studies using true population-based rather than voluntary samples of patients and thorough case-finding methods would help to clarify whether MS is on the rise among women or if the changes reported in this most recent study primarily reflect the evolution and more appropriate use of diagnostic tools.