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Psoriatic Arthritis at a Glance
  • Psoriatic arthritis (PsA) is an inflammatory arthritis associated with psoriasis and seronegative for rheumatoid factor.
  • Genetic and environmental factors underlie susceptibility to PsA and immune-mediated inflammation leads to inflammation in musculoskeletal structures.
  • Clinical features of PsA include peripheral and axial arthritis, enthesitis, dactylitis, and tenosynovitis.
  • Extra-articular involvement in addition to skin and nail involvement may include conjunctivitis, uveitis, and inflammatory bowel disease.
  • Investigations may reveal elevated acute phase reactants, although conventional tests such as erythrocyte sedimentation rate and C-reactive protein are normal in up to 50% of patients.
  • Radiographs may reveal soft-tissue swelling, periostitis, erosions, pencil-in-cup change, ankylosis, sacroiliitis, or syndesmophytes.
  • Pharmacotherapy is the mainstay of treatment, and antitumor necrosis factor agents are safe, efficacious, and effective.

Psoriatic arthritis (PsA) is an inflammatory musculoskeletal disease that affects people with psoriasis or their near relatives. It affects musculoskeletal structures such as the peripheral and axial joints, entheses, and tendon sheaths. The eye and mucous membranes are also often involved. Thus, the disease has varied manifestations that make diagnosis and assessment sometimes difficult.

The original case definition for PsA was provided by Moll and Wright in 1973.1 They defined PsA as an inflammatory arthritis associated with cutaneous psoriasis, seronegative for rheumatoid factor. Rheumatoid factor is a marker for rheumatoid arthritis (RA); thus, the definition was meant to help distinguish PsA from RA, which at that time was a more recognized form of inflammatory arthritis. The CASPAR study group recently developed a new set of criteria for classification of PsA using data collected prospectively in patients with long-standing disease (Box 19-1).2 The CASPAR criteria had specificity of 98.7% and sensitivity of 91.4% in the original study, with excellent sensitivity in both early and late disease. The criteria allow classifying patients even when they do not have current, past, or family history of psoriasis and are now used in epidemiologic and genetic studies in PsA.

Box 19-1 the Caspar Criteria

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