Recent studies have found that sexual dimorphism plays a role in ankylosing spondylitis. Sexual dimorphism refers to physical differences between females and males of a species that go beyond sexual organs.
Although there are many similar gene expression patterns in men and women with ankylosing spondylitis, male patients have more genetic alterations than women.
Research from 2016 showed that men with ankylosing spondylitis have a high level of Th17 and IL-17A cells. These are inflammatory cells in the body, and women with ankylosing spondylitis did not have elevated levels of these cells.
Previously, it was established that ankylosing spondylitis impacts more men than women. However, recent studies have debunked this claim, showing that the likelihood of the disease is relatively the same in both sexes.
Part of the reason many older studies had skewed results was the smaller number of women in the analyses. Since the studies were not stratified for gender distribution, the results often showed a higher likelihood of men getting the disease.
Recent studies show a decline in the male to female ratio in patients with ankylosing spondylitis in Switzerland from 1980 to 2016.
Moreover, the age at which AS shows its symptoms in males and females also does not differ. However, females have a longer delay in diagnosis.
A 2017 study showed that women tend to wait an average of 8.8 years before being diagnosed. Men get a diagnosis in 6.5 years on average. Since there is no single test to diagnose ankylosing spondylitis, a rheumatologist must check medical history, evaluate symptoms, and do a physical exam.
Different Clinical Expression in Men and Women
After declaring itself, ankylosing spondylitis has a different clinical expression in men and women. Pelvic and spinal X-rays have shown that ankylosing spondylitis causes more radiographic changes in men as compared to women.
Men also have more advanced joint fusion and erosive damage than women.
While it's true that ankylosing spondylitis impacts men more than women, the difference is not as large as it was previously thought to be. A Canadian study looked at the number of men and women diagnosed with ankylosing spondylitis from 1995 to 2010. The results showed that, even though men were more commonly diagnosed than women, the male to female ratio had decreased over time. It was 1.70 in 1995 and 1.21 in 2010.
Possible Causes
A 2011 study investigated the number of cumulative outpatient visits for ankylosing spondylitis by men and women. The study involved 636 men and 228 women. The researchers found that men had a higher number of hospitalizations due to ankylosing spondylitis.
This could be due to two reasons. First, men have a worse severity of ankylosing spondylitis as compared to women. Because of this, they are more likely to go for outpatient visits or be hospitalized.
Second, there is often a delay in the female diagnosis of ankylosing spondylitis because the condition is predominantly known as a male disease. Since women find out about their diagnosis later, their utilization of healthcare resources is also underestimated in many studies.
