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INTRODUCTION

DEFINITION

Psoriatic arthritis is a chronic inflammatory arthritis that affects 5–30% of persons with psoriasis. Some pts, especially those with spondylitis, will carry the HLA-B27 histocompatibility antigen. Onset of psoriasis usually precedes development of joint disease; approximately 15–20% of pts develop arthritis prior to onset of skin disease. Nail changes are seen in 90% of pts with psoriatic arthritis.

PATTERNS OF JOINT INVOLVEMENT

There are 5 patterns of joint involvement in psoriatic arthritis.

  • Asymmetric oligoarthritis: often involves distal interphalangeal/proximal interphalangeal (DIP/PIP) joints of hands and feet, knees, wrists, ankles; "sausage digits" may be present, reflecting tendon sheath inflammation.

  • 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.

  • Hypoproliferative anemia, elevated erythrocyte sedimentation rate (ESR).

  • Hyperuricemia may be present.

  • 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 172-1THE CASPAR (CLASSIFICATION CRITERIA FOR PSORIATIC ARTHRITIS) CRITERIAa

TREATMENT ...

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