Some patients with psoriasis go on to develop psoriatic arthritis (PsA), which is often unrecognized for years. Early screening, diagnosis, and treatment are key to help prevent structural damage and improve long-term clinical outcomes. Additionally, due to the current lack of PsA-specific biomarkers, early rheumatology referrals are imperative for prompt diagnosis and treatment initiation.

Approximately 30% of patients with psoriasis are eventually diagnosed with PsA, and, while the majority of patients with PsA have been previously diagnosed with psoriasis, most go approximately 10 years before they notice any signs of musculoskeletal disease. Patients with PsA present with swollen joints, localized pain in areas where tendons/ligaments insert into bone (eg, the spine and Achilles tendons), dactylitis, and/or enthesitis. Additionally, a large number of patients with PsA also experience spondylitis, which is marked by an immunologic inflammation of the spine.

Ultimately, PsA can be quite variable in its presentation and is distinct from other forms of arthritis, including osteoarthritis and rheumatoid arthritis. For instance, the swelling of joints is very distinctive. In osteoarthritis, patients have hard bony enlargements in the joints, whereas the swelling in patients with PsA has a “squishy” feel due to the proliferative synovitis. In rheumatoid arthritis, the number of affected joints is typically greater, and the symptoms are quite symmetrical.

When it comes to diagnosing PsA, unfortunately, there is currently no single biomarker that we can use; however, various research groups are working hard on identifying such a biomarker. If the disease has been present for a while, plain x-rays can show characteristic joint damage, while an ultrasound or a magnetic resonance imaging scan can detect evidence of inflammation in peripheral joints, entheses, and the spine. There are also some questionnaires that can be used by dermatologists to screen for PsA in their patients with psoriasis. My favorite is the Psoriasis Epidemiology Screening Tool (PEST) questionnaire, which includes 5 really simple questions. The key is getting a referral to a rheumatologist as soon as the first signs of PsA arise.

One key study that helped us understand the importance of the early diagnosis of PsA found that if the diagnosis was within 6 months of symptom onset, patients had better outcomes compared with those who were diagnosed much later. Some of the findings included less structural damage, better function, very few joints involved, and overall better outcomes with less destructive changes and better physical performance. Similarly, using the CorEvitas Psoriatic Arthritis/Spondyloarthritis Registry, our group found that diagnosing and initiating treatment for PsA less than 1 year from symptom onset resulted in more patients achieving minimal disease activity, while another study found that making the diagnosis within 2 years of symptom onset was accompanied by much better outcomes, better function, and less likelihood of having joint damage.

We still treat PsA with conventional synthetic DMARDs such as methotrexate, but we are increasingly moving toward the early initiation of biologic therapy or targeted synthetic DMARD therapy. Many of the patients we see are referred from dermatology practices and are already receiving a biologic (eg, IL-17, IL-23, or TNF inhibitor therapy) for the skin and nail manifestations of psoriasis. However, despite improvement in cutaneous psoriasis, they now have musculoskeletal symptoms, and even though these medicines are typically effective for treating arthritis, sometimes they are not. So, if a patient has evidence of inflammation in the joints or at entheseal insertion sites, particularly if there is any evidence of joint damage, loss of function, or impaired quality of life, we focus on either switching from their current biologic medication or initiating, for the first time, this advanced class of immune-modulating medications that are so effective for our patients with PsA.