Historically, it was widely understood that in some people with psoriasis, psoriatic arthritis would develop later on — typically years after skin symptoms appeared. But research has shown that the relationship between skin and joint symptoms may be more complicated in some people.
“There are people who get both at the same time,” says Eric Ruderman, MD, a rheumatologist at Northwestern Medicine in Chicago. “And there are people who get joint symptoms first, that look like psoriatic arthritis, but they don’t have psoriasis. Yet a few years later they develop a patch of psoriasis, or they have a strong family history of psoriasis.”
About 30 percent of people with psoriasis will develop psoriatic arthritis, usually within 10 years. Both conditions involve inflammation, in which the immune system overacts in destructive ways — leading to out-of-control skin cell growth in psoriasis, and joint swelling and pain in psoriatic arthritis.
“Psoriasis and psoriatic arthritis are increasingly understood as manifestations of a single overarching ‘psoriatic disease’ continuum,” says Rebecca Gordon, MD, a rheumatologist at UCHealth Cherry Creek Medical Center in Denver. Dr. Gordon notes that both conditions share the same set of immune system pathways, with an established biological “bridge” between skin and joint disease activity.
This “bridge” involves what are known as cytokines, immune system proteins that play a role in inflammation. In what’s known as the IL-23/IL-17 axis, a cytokine called IL-23 supports immune cells that release another cytokine called IL-17 — which promotes inflammation that plays a role in both skin and joint disease.
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