Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (12 page)

   The Classification Criteria for Psoriatic Arthritis (CASPAR) require the presence of joint, spine, or entheseal inflammatory disease plus a minimum score of 3 points from the following five categories (98.7% specificity and 91.4% sensitivity):

   Current psoriasis (2 points); personal or family history of psoriasis (1 point)

   Typical psoriatic nail dystrophy (1 point)

   Negative rheumatoid factor (1 point)

   Current dactylitis or history of dactylitis (1 point)

   Hand or foot plain radiography demonstrating juxta-articular new bone formation (1 point)

   Who Should Be Suspected?

   Most patients who develop PsA have skin symptoms of psoriasis first (erythematous papule and plaques with a silver scale), followed later by arthritis symptoms characterized by pain, tenderness, and stiffness in the joints and back.

   Several HLA types have been identified to be associated with PsA, suggesting a genetic predisposition. This is also indicated by the presence of a family history of psoriasis and psoriatic arthritis in up to 40% of patients.

   Laboratory Findings

Laboratory finding are not specific.

   ESR and CRP are elevated in approximately 50% of cases; levels correlate with the number of involved joints.

   RF is negative.

   Anemia of inflammation, hypergammaglobulinemia with increased IgA levels, and hypoalbuminemia have been reported in some cases.