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ESSENTIALS OF DIAGNOSIS

  • Psoriatic arthritis (PsA) is a chronic, immune-mediated disease that affects both the skin and joints.

  • Clinical manifestations are diverse; however, hallmark features include asymmetric inflammatory arthritis, skin and nail psoriasis, enthesitis, and dactylitis.

  • About one-third of patients with psoriasis will develop PsA.

  • Patients with PsA are seronegative, lacking both rheumatoid factor and anti-CCP antibody.

  • Radiographic findings of erosions, periosteal reaction, ankyloses, and juxta-articular new bone formation can occur.

GENERAL CONSIDERATIONS

Psoriatic arthritis (PsA) is a chronic, immune-mediated disease associated with both inflammatory arthritis and skin psoriasis. The prevalence of PsA varies in the United States from 6 to 25 cases per 10,000 people (Ogdie and Weiss, 2015). This wide range in prevalence is attributed to the lack of consensus on the case definition of PsA. The mean age of disease onset ranges from 30 to 55 years, with men and women equally affected. Up to 30% of patients with psoriasis can develop PsA. Patients with PsA often suffer from impaired function and reduced quality of life. PsA is also associated with a higher risk of certain comorbidities, including the increased risk of cardiovascular disease associated with hypertension, hyperlipidemia, diabetes, obesity, and metabolic syndrome, as well as ophthalmologic disease, osteoporosis, and inflammatory bowel disease.

PsA patients present in a heterogeneous manner, the diverse clinical features of which often lead to a delay in diagnosis. Patients can present with either an asymmetric oligoarthritis, an symmetric polyarthritis, or an arthritis of the axial skeleton (ie, the sacroiliac joints and spine). Any of these presentations may be accompanied by periarticular involvement with dactylitis (a “sausage digit”) or enthesitis, defined as inflammation at a point at which a tendon inserts into a bone. Skin psoriasis can accompany the joint symptoms, including manifestations such as plaque psoriasis over extensor surfaces, psoriasis predominantly affecting the scalp or nails, or pustular psoriasis on the palms and soles. Despite tremendous growth in the number of approved therapies for patients with PsA, the effects of approved medications are variable with regard to their joint and skin outcomes. The disease heterogeneity of PsA heightens the challenges of selecting the best therapeutic options and improving overall health outcomes.

Pathogenesis

The etiology of PsA is not completely understood, but our understanding of its pathogenesis is evolving. It is hypothesized that both genetic and environmental factors can trigger an aberrant inflammatory response in various organ systems beyond the skin and joint manifestations of PsA. In contrast to rheumatoid arthritis, a disorder in which the synovial is recognized as the primary articular site of inflammation, in PsA the primary site of inflammation is the enthesis. Enthesitis is a distinguishing feature in the pathogenesis of PsA but can also occur more broadly in patients with any of the seronegative spondyloarthropathies (Ferguson et al, 2019).

T cells are important in the pathophysiologies of both ...

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