Definition

PsA is a chronic inflammatory arthritis that affects up to 30% of persons with psoriasis. HLA-B27 is found in 50-70% with axial disease but <20% of pts with only peripheral involvement. Onset of psoriasis usually precedes development of joint disease; approximately 15-20% of pts develop arthritis prior to onset of skin disease. Nail changes occur in most pts with PsA, dactylitis and enthesitis are common in PsA and help to distinguish it from other joint disorders.

Patterns of Joint Involvement

There are five patterns of joint involvement in PsA, which can overlap:

• Asymmetric oligoarthritis: often involves distal interphalangeal/proximal interphalangeal (DIP/PIP) joints of hands and feet, knees, wrists, ankles.
• Symmetric polyarthritis (40%): resembles rheumatoid arthritis except rheumatoid factor is negative, absence of rheumatoid nodules.
• Predominantly DIP joint involvement (15%): high frequency of association with psoriatic nail changes.
• “Arthritis mutilans” (3-5%): aggressive, destructive form of arthritis with severe joint deformities and bony dissolution.
• Spondylitis and/or sacroiliitis: axial involvement is present in 20-40% of pts with psoriatic arthritis; may occur in absence of peripheral arthritis.

Evaluation

• Negative tests for rheumatoid factor.
• Anemia, elevated ESR.
• HIV infection should be suspected in fulminant disease.
• Inflammatory synovial fluid and biopsy without specific findings.
• Radiographic features include erosion at joint margin, bony ankylosis, tuft resorption of terminal phalanges, “pencil-in-cup” deformity (bone proliferation at base of distal phalanx with tapering of proximal phalanx), axial skeleton with asymmetric sacroiliitis, asymmetric nonmarginal syndesmophytes.

Diagnosis

(Table 163-3 The CASPAR (Classification Criteria for Psoriatic Arthritis) Criteriaa )