Who Does Axial Spondyloarthritis Affect?
In order to learn more about a disease, the epidemiology of the disease is studied. Epidemiology involves the study of the way a disease affects populations. This includes the frequency and prevalence of a disease, causes and risk factors, and various geographic areas and population characteristics of a disease.1 Epidemiology can also be used in evaluating the treatment or control of health problems.1
Epidemiology looks at the macro or bigger picture, to help scientists and health professionals treat the more micro, or more individual, aspects of a disease. Each person is part of a larger group, whether it’s broken down into family, gender, racial/ethnic groups, or geographic location. Having broad-scale information can be valuable in treating individuals, and that’s what epidemiology provides.
Getting accurate data for AxSpA can be challenging due to significant differences in reporting rates and under-diagnosis. AxSpA has also not been researched extensively.2
How prevalent is AxSpA?
AxSpA is an umbrella term. A diagnosis of AxSpA can include non-radiographic AxSpA, radiographic AxSpA, ankylosing spondylitis (AS), as well as various other kinds of spondyloarthritis conditions.2 In the US, the population prevalence of AxSpA is about 0.9 to 1.4 percent, or 1.7-2.7 million people.3
AxSpA is still a fairly new diagnostic classification. Because there is so much overlap with AS, the statistics and research may be scarce or focus more on AS than other conditions on the AxSpA spectrum. As more professionals study the condition and treat more people with AxSpA, more data and information will become available.
The approximate delay in diagnosis of AxSpA is 14 years in the US.3 Many doctors or health care providers may not be aware of the symptoms. Furthermore, symptoms usually develop gradually and do not cause changes that can easily be seen in blood work or imaging, making diagnosis challenging. The delayed diagnosis results in inaccurate prevalence rates.
It usually becomes symptomatic in late adolescence and early 20s. Many times, someone may have lower back pain but because of their young age, they and their health care providers may not be looking for a chronic health condition, and instead attribute the pain or discomfort to something else.
Gender differences in AxSpA
On average, women have been found to have a lower age of onset of AS disease onset (21.5 years vs 23.6).3 Women with AxSpA are also more likely to have a family history of AS and have less progression seen on X-rays.3
AS has been found to affect men two to three times more often than women.4
Racial/ethnic differences in AxSpA
AxSpA was found to be more common in non-Hispanic whites and Mexican Americans (1.5 percent each) than Blacks/African Americans (0.9 percent).3 It is hypothesized that this may be related to the lower frequency of HLA-B27 in Blacks/African Americans than in non-Hispanic whites and Mexican Americans.3
Risk factors for AxSpA
Genetics plays a large role in developing AxSpA and AS. Family members of an affected individual are more at risk of developing the condition, but it also partly depends on whether they inherited the HLA-B27 gene.4
There may also be environmental factors involved. Having been breastfed has been found to be associated with a lower risk of AS.5 It is hypothesized that having been breastfed may influence the microbes in the gut.6 Having more childhood infections like respiratory tract infections was also found to be associated with AS.6
More research will need to be done to examine possible risk factors for AxSpA and the spectrum of conditions it covers.