Ankylosing Spondylitis vs. Rheumatoid Arthritis: And The Diagnosis Is...?

Last updated: February 2022

When diagnosed with ankylosing spondylitis (AS), I had never heard of it until a chiropractor asked, “Has anyone ever told you that you have AS?” “No; what the heck is AS?” I wondered. Then the chiropractor explained and it started to make sense, mostly.

I received my diagnosis of rheumatoid arthritis (RA) in 2000, things were going well, and I had no reason to question the diagnosis or method of treatment. But my back and hips still hurt every day.

Learning about ankylosing spondylitis at a critical moment

I was seeing the chiropractor at the suggestion of a neurologist to work on balance issues and provide some relief for chronic back pain. Each time I would go in, the chiropractor would jerk me, my back would pop, and I would feel great.

Then I would walk out of the office and get maybe 20 steps away from the door, and my back would shift, pop, and everything would go back to where I was before the visit. In one of these therapeutic sessions, he raised the issue of AS. That was in 2015, and his comment, though not a diagnosis, was a milestone in my path forward.

Ankylosing spondylitis and rheumatoid arthritis

When I saw my rheumatologist next, I asked him about the comment. He mostly passed it off with a smile and nod. There was a good reason for not taking AS seriously. According to Barczyńska, Węgierska, Żuchowski et al., the coexistence of RA and AS in the same person is rare.1 But at the same time, it is not unheard of. The same authors who found the coexistence of the two conditions is unlikely wrote, “It is possible that the rarely described phenomenon of RA and AS coexistence may be more widespread than previously thought.”1

Uncertain criteria

Since the conditions can have similar manifestations, the clinician faces uncertain criteria in how to make a judgment about which patients have which one. The common opinion is that AS has a higher tendency in males, while RA has a higher tendency in women.2 Yet, we know that many women have AS. A large fifteen-year population study in Ontario, Canada, between the years of 1995 to 2010 came to this conclusion:

Men had higher prevalence than women, but the male/female prevalence ratio decreased from 1.70 in 1995 to 1.21 by 2010. A higher proportion of male compared with female patients with AS were diagnosed in the 15–45 age group. Annual incidence rates revealed increasing diagnosis of AS among women after 2003.3

Ankylosing spondylitis diagnosis in women

This study found that women were being diagnosed with AS at an increasingly higher rate after 2003 in Ontario, Canada.3 The study authors did not make a judgment as to why there was an increasing number of women diagnosed with AS. As a casual observer of the results, I suggest that greater acceptance that women can have AS by clinicians likely led to a greater percentage of diagnoses.

As a patient, I tend to see many women in AS forums and as writers of blogs. This anecdotal evidence demonstrates to me that yes, women do have AS and that the possibility of having the condition should inform the clinician that a woman may have AS.

My AS diagnosis and treatment journey

In my diagnosis journey, I came to appreciate the difficulty faced by women on their journey to diagnosis. Each time I raised the issue with my rheumatologist, he reminded me that the treatment was working well.

Treating inflammation

It appears that using my current biologic medication had stopped the many problems that RA or AS had caused in my life from getting worse. In the opinion of my rheumatologist, it does not matter if I have AS or RA or both. He treats inflammation, and using my biologic medication made my inflammation low.

Testing for HLA-B27

Still, at my insistence, my doctor decided to seek verification as to whether I had AS or not. So he did what most doctors do, he ordered blood work to determine if I was HLA-B27 positive. According to Sheehan:

In the UK, HLA-B27 is present in 90–95 percent of patients with ankylosing spondylitis, 60–90 percent of patients with reactive arthritis, 50–60 percent of patients with psoriatic arthritis or inflammatory bowel disease and spondylitis, and 80–90 percent of children with juvenile ankylosing spondylitis.4

Limitations of HLA-B27 testing

Given that the HLA-B27 is associated with so many conditions, ordering that test makes sense. But, this test has one major limitation: it cannot be used as the sole determinant for the presence of AS. In 1982 Khan and Khan reported that the “data also show that the B27 test is not clinically useful as a screening test for ankylosing spondylitis, that is, for identifying patients in an unselected population.”5

The term unselected population might be confusing. What it means is that this test alone, absent clinical evaluation, patient history, physical examination, and imaging cannot be used to determine if a patient has AS.

Confirming my AS diagnosis with surgery and imaging

In 2012 when my doctor had the results of the HLA-B27, he added the diagnosis of ankylosing spondylitis to my list of maladies. Over time, that diagnosis has been confirmed with surgery and imaging. Each time I ask the surgeon, “Do you think I have AS?”, the answer has always been, “Yes, your spine is proof of the diagnosis.”

Incidentally, if you are interested, I suggest you check out This is one of the best communities on the internet, focusing on RA. You might even recognize one of the writers there.

By providing your email address, you are agreeing to our privacy policy.

This article represents the opinions, thoughts, and experiences of the author; none of this content has been paid for by any advertiser. The team does not recommend or endorse any products or treatments discussed herein. Learn more about how we maintain editorial integrity here.

Join the conversation

Please read our rules before commenting.

Community Poll

Have you taken our In America Survey yet?