Psoriatic arthritis is an inflammatory arthritis that ultimately occurs in approximately one-third of patients with psoriasis at some point in their disease course. There are several different presentations, including enthesitis, which is inflammation at the sites where tendons and ligaments insert into bones; dactylitis, which is inflammation of the small joints of the hands and feet that is associated with periarticular swelling; inflammatory arthritis in the spine; and inflammatory arthritis of the small joints, similar to rheumatoid arthritis. When psoriatic arthritis develops in someone with psoriasis, it often occurs approximately 10 to 11 years after the cutaneous manifestations. If psoriatic arthritis is not diagnosed and adequately treated, it can cause significant morbidity. Considering the prevalence and severity of psoriatic arthritis, I think that it is important for dermatologists to evaluate their patients with psoriasis for joint symptoms on a regular basis.

We are not necessarily able to predict which individuals with psoriasis will ultimately develop psoriatic arthritis. Some clinicians believe that, if you begin treatment with a highly effective systemic therapy that also targets the joints at the beginning of psoriasis treatment (ie, before the development of psoriatic arthritis), you might prevent the further deterioration of the joints. Nonetheless, when patients with psoriasis develop psoriatic arthritis, they need to be treated aggressively, because the joints can progressively worsen and become deformed.

In my assessments of patients with psoriasis, I ask questions related to their joints. For example, do they hurt and/or feel stiff? Do they swell? Which joints? If the answer is yes, then I determine the timing of the stiffness/pain. For example, does it occur when they wake up? Do they have to work the stiffness out a bit to get going, or does the stiffness increase as the day goes on? Patients with psoriatic arthritis tend to be stiff in the morning when they wake up and then for 30 minutes or so afterward. However, when these symptoms get worse as the day progresses, noninflammatory arthritis or osteoarthritis may be the explanation. I also examine the joints for swelling and tenderness, especially the distal and proximal interphalangeal (ie, DIP and PIP, respectively) joints.

Patients with psoriatic arthritis frequently have nail disease, so examining the fingernails can reveal important clues. The nails are often associated with psoriatic arthritis because the extensor tendon for the DIP joint goes right under the nailbed. Therefore, if the DIP joint is inflamed, the nail will be as well, and you will likely note nail changes. Interestingly, approximately 5% of patients with psoriasis present with psoriasis in their nails only, and many of these individuals also have psoriatic arthritis. Therefore, when a patient presents with abnormal fingernails typical of psoriasis, psoriatic arthritis should be ruled out.

There is no specific blood test to diagnose patients with psoriatic arthritis; interestingly, the high-sensitivity C-reactive protein level is frequently elevated in psoriatic arthritis, but not in psoriasis. Screening questionnaires have been developed to help dermatologists and primary care physicians identify those who should be seen by a rheumatologist. After a patient is diagnosed with psoriatic arthritis, they may need a systemic treatment (ie, either an oral small-molecule inhibitor such as apremilast or a biologic) to treat the psoriatic arthritis.