There are more than 100 autoimmune diseases in all, and the list is growing, notes Amber L. Champion, MD, an endocrinologist at the Kirk Kerkorian School of Medicine at the University of Las Vegas in Nevada. “They are a diverse group of diseases and affect nearly every organ system of the body,” she says. Autoimmune diseases share certain traits. With all autoimmune diseases, the body’s immune system goes into overdrive, and essentially begins attacking the body itself, as happens with psoriatic arthritis (PsA). There is a strong link between psoriasis and psoriatic arthritis: According to the National Psoriasis Foundation, an estimated 30 percent of people with psoriasis also develop psoriatic arthritis. If you have both psoriasis and psoriatic arthritis, your risk of an additional autoimmune disease may be even higher, according to a review in the International Journal of Molecular Sciences published in October 2020. Genetic, environmental, and immune factors may all be to blame, according to the authors. Chronic inflammation may also be involved. RELATED: Your Head-to-Toe Guide to Easing Psoriatic Arthritis Symptoms
Psoriatic Arthritis vs. Rheumatoid Arthritis
If you have psoriasis and consistently experience joint pains and aches, you should see your healthcare provider. That’s because joint pain can be a symptom of psoriatic arthritis and rheumatoid arthritis — both very real possibilities for people with psoriasis. Indeed, a study published in the Journal of the American Academy of Dermatology in June 2021 found that adults with psoriasis experience an increased likelihood of having rheumatoid arthritis compared to adults without psoriasis. Determining whether you have psoriatic or rheumatoid arthritis can be challenging, but making the distinction is important, says Natalie E. Azar, MD, a clinical assistant professor of medicine and rheumatology at New York University Langone Medical Center in New York City. Although rheumatoid arthritis and psoriatic arthritis share many traits — joint pain, stiffness, swelling — they also have unique symptoms. For instance, psoriatic arthritis symptoms can include a skin rash as well as nail damage. It’s important to distinguish which type of arthritis you have to manage it well and know what to expect, Dr. Azar says. “Although treatment options can be strikingly similar,” Azar says, “significant advances have been made in the development and discovery of new biologic therapies very specifically for psoriatic arthritis.” RELATED: The Consumer’s Guide to Biologics for Psoriatic Arthritis
How to Get the Right Arthritis Diagnosis
There is no single test for psoriatic arthritis, says Azar. Along with a physical exam, you’ll likely need a series of both imaging procedures and blood tests for a diagnosis, and to rule out other forms of arthritis, such as rheumatoid arthritis or gout. There’s no one test to diagnose rheumatoid arthritis either, but, as with PsA, blood tests are part of the workup. The presence of autoantibodies in the bloodstream, either rheumatoid factor (RF) or cyclic citrullinated peptide (CCP) antibodies, will suggest an RA diagnosis. These antibodies tend to be less typical in people with psoriatic arthritis, according to an article published in Rheumatic and Musculoskeletal Diseases in August 2018. As part of the physical exam, the doctor will closely evaluate the affected joints. “RA involves the joints in a symmetrical fashion, and often, when rheumatoid factor is very high, there may be nodules under the skin,” Azar says. According to the National Rheumatoid Arthritis Society, 20 percent of patients with RA develop these firm lumps. Psoriatic arthritis, on the other hand, can reveal itself in a variety of ways, affecting a large joint or a single small finger joint of the hand, says Azar. Another notable difference between the two diseases is bone involvement. “RA is characterized by bone loss or erosion near the joint, while PsA is marked by both bone erosion and new bone formation,” Azar says. An X-ray or other imaging method can help reveal what’s going on. Rheumatoid arthritis affects mainly the joints, while psoriatic arthritis may also involve inflammation of the entheses — the areas where ligaments or tendons attach to bones. Common locations for enthesitis include the bottom of the foot, the Achilles tendon, and locations where ligaments connect to ribs, spine, and pelvis, according to the National Psoriasis Foundation. People with psoriatic arthritis often experience recurrent bouts of tendinitis, plantar fasciitis, and other painful foot conditions. This is not commonly the case for rheumatoid arthritis. PsA can involve the spine, too; 20 percent of people with psoriatic arthritis develop the spine condition spondylitis or sacroiliitis, both painful and both usually absent in people with RA. A scan called an MRI can be a good way to spot sacroiliitis, according to a study published in July 2020 in Scientific Reports. RELATED: What Psoriatic Arthritis Really Feels Like Additional reporting by Paula Derrow.
