By Sophia Cariati, Society for Women Health Research InFocus, Vol. 10, No. 1, March 2002
The proportion of women living with multiple sclerosis jumped by 50 percent between the 1980s and the 1990s, while the number of men living with the disease remained constant, according to new findings from the U.S. Department of Health and Human Services. This information, combined with the fact that autoimmune diseases such as multiple sclerosis are the fourth leading cause of disability among American women, underscores the need for further research into one of the most poorly understood categories of illness.
Multiple sclerosis (MS) is a chronic disease in which immune cells attack the insulating covering, or myelin sheath, surrounding nerve fibers in the brain and spinal cord. The hallmark symptoms include muscle weakness and stiffness, impaired balance and coordination, numbness and blurred vision. MS and other autoimmune diseases are characterized by the body misdirected attack on its own healthy tissue.
Virtually all autoimmune diseases, MS included, are more common in women than in men. In fact, for unknown reasons, women make up about 75 percent of all autoimmune disease sufferers. A slew of other sex differences exist in autoimmunity, including the fact that multiple sclerosis typically progresses more quickly in men than in women.
Upward Trend in Women Revealed
Epidemiologist Curtis Noonan, Ph.D., and colleagues at the Agency for Toxic Substances and Disease Registry (ATSDR) in Atlanta, Georgia, examined national survey data to determine the prevalence of MS in the U.S. Until their report, the only national data on the disease was based on an outdated 1976 survey. Several federal and local public health offices have received inquiries from citizens concerned that they might have an exceptionally high number of MS cases in their communities, according to Noonan.
"Public health organizations didnt have the basic information needed to answer the question of how many cases [of MS] is normal and how many cases is high," said Noonan. "The data that existed were outdated."
Noonan found that the number of MS cases increased by 50 percent from the early 1980s to the mid-1990s from 75 per 100,000 women to 113 per 100,000. In the same time period, the number of cases of MS among men remained relatively constant. This growing prevalence of MS among women backs up results of other recent studies.
In agreement with prior statistics, Noonan found that, on average, female MS sufferers outnumbered males by 2.6 to 1. For both men and women, MS prevalence was highest among people in their 40s and 50s. In addition, white women were more likely to have MS compared with women of other races. What?s more, the number of women living with MS was significantly lower in southern states compared with northern areas of the country.
What accounts for the observed trend? There is no hard fast answer, says Noonan. But there are a few possible explanations. The study may have revealed a true increase in the number of new cases of MS in women. Conversely, better disease detection and improved treatments may account for the growing number of women living with MS. If this were the case, however, Noonan would have expected to see a similar increase in prevalence among men.
Why Women?
Exactly why women are more prone to multiple sclerosis and other autoimmune diseases remains a mystery. Finding the answer to this question may yield improved treatments, prevention strategies, and maybe even a cure for both sexes.
Accumulating evidence suggests that understanding how a woman immune system reacts to pregnancy may help unlock the mysteries of autoimmune disease. Symptoms of MS often subside during pregnancy but worsen or occur for the first time soon after giving birth. A number of studies suggest that the cells that travel from mother to the fetus and vice versa during pregnancy may trigger the diseases.
Until recently, many researchers blamed fluctuating hormones for the pregnancy-induced changes in MS. And while they are undoubtedly involved, they may be just a piece of the puzzle. Michael D. Lockshin, MD, director of the Barbara Volcker Center for Women and Rheumatic Diseases, Cornell University, believes that the interaction between a woman immune system and her environment is an important area that has been largely understudied.
"Hormones are unequivocally involved [in the sex differences], said Dr. Lockshin. "They are, however, in my belief, part of the process, not the cause."
Research also suggests that a person genes play a role in determining her susceptibility to MS. Some families are particularly prone to autoimmune disease. Interestingly, in such families, different family members often develop different diseases. For example, a woman may have MS; her sister might have lupus; and her aunt, rheumatoid arthritis.
For more information, visit the Society for Women Health Research Web site at www.womens-health.org.
References: Noonan CW, Kathman SJ, White MC. Prevalence estimates for MS in the United States and evidence of an increasing trend for women. Neurology 2002 Jan 8;58(1):136-8; Nelson JL. HLA relationships of pregnancy, microchimerism and autoimmune disease. J Reprod Immunol 2001 Oct;52(1-2):77-84; Johnson KL, Nelson JL, Furst DE, et al. Fetal cell microchimerism in tissue from multiple sites in women with systemic sclerosis. Arthritis Rheum 2001 Aug;44(8):1848-54.
Reprinted with permission of the Society for Women?s Health Research-January 25, 2002
