Most forms of multiple sclerosis strike women twice as often as men. Primary progressive MS, though, affects men and women in nearly equal numbers, baffling researchers. Here's what's understood at this point:
The 'Equal Opportunity' MS
Primary progressive MS is marked by a steady march of symptoms from the time of diagnosis. There are no attacks followed by later improvement, as in the more common forms of MS.
Recent studies show that gender differences in primary progressive MS vary according to age. In the largest studies done so far, hundreds of men and women with primary progressive MS were followed for decades:
- Under age 30, equal numbers of men and women were affected.
- Among people developing MS at ages older than 45 there were more women than men.
- Almost two women for each man were diagnosed with primary progressive MS after age 50 -- still short of the rates in other forms of MS.
When it comes to disease severity, primary progressive MS is also unique. MS in men is usually more severe than in women. But large studies of primary progressive MS show:
- Early on, men and women had equal disease severity and rates of progression.
- After about 20 years of living with primary progressive MS, men's disease finally began to "outrun" the women's in severity.
Why the differences? At this point, there are more questions than answers. As in other forms of MS, sex hormones may well be involved. There are clues in the chemistry and the MRI scans of the brains of people with primary progressive MS. But research into this form of multiple sclerosis is only beginning.
Men vs. Women in All Types of Multiple Sclerosis
Among people who develop all types of MS before the age of 20, women outnumber men by 3 to 1.
Looking at people of all ages, at least twice as many women as men are living with MS. But the ratio of women to men with MS may be rising even higher. Some recent estimates place the number at 4 to 1 -- and suggest it is still going up.
Sex Hormones and Multiple Sclerosis
Multiple sclerosis doesn't target all women equally. Nearly always, MS attacks during the childbearing years. Symptoms often increase after childbirth or at the end of a menstrual cycle.
When men develop multiple sclerosis, it's more often in their 30s or 40s -- just about the time their testosterone levels start to decline.
Taken together, these clues suggest that sex hormones, like estrogen and testosterone, may be involved. It may be the balance of hormones, rather than their actual levels, that's most important.