Ankylosing Spondylitis with Psoriasis vs. Psoriatic Arthritis with Back Pain

About 25% of people who have an autoimmune condition develop at least one more; some people live with three, four, or more. In fact, certain pairs of inflammatory diseases commonly occur together.

For one, people with ankylosing spondylitis (AS) (also known as axial spondyloarthritis) — which is best-known for causing chronic lower back pain — are also more likely to have psoriasis — an autoimmune disease that manifests in the form of scaly red and silvery skin patches. That combination might sound pretty similar to the autoimmune condition psoriatic arthritis (PsA), which, by definition, is a form of inflammatory arthritis that typically causes joint pain as well as skin plaques.

To further add to the confusion, PsA is considered part of the same family of rheumatic diseases as ankylosing spondylitis — they’re both considered types of spondyloarthritis, which is an umbrella term for a group of types of arthritis that have similar traits in common.

And while most psoriatic arthritis patients develop arthritis in the small joints of the fingers and toes, the joints in the back can sometimes be impacted. PsA patients who have arthritis in the back or sacroiliac joints in the pelvis may be told that they have “axial PsA.”

If the sometimes overlapping details of these conditions are making you wonder if people with AS and psoriasis really have axial PsA, you’re in good company. Researchers at the University of Toronto weren’t sure, either. To find out, they compared data on more than 2,000 patients. One group had been diagnosed with AS and psoriasis; another had been diagnosed with axial PsA; and a third had only been diagnosed with AS (without psoriasis).

According to their findings, which appear in the journal Rheumatology, axial PsA is not, in fact, the same thing as AS plus psoriasis.

The researchers found that AS patients (with or without psoriasis) were more apt to be male, more likely to be positive for HLA-B27 (a genetic marker), and much more likely than those with PsA to report back pain as a chief complaint.

“AS patients, with or without psoriasis, seem to be different demographically, genetically, clinically, and radiographically from [axial PsA] patients. [Axial PsA] seems to be a distinct entity,” they concluded.

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