Psoriatic arthritis.

Despite having several modes of presentation, psoriatic arthritis usually can be readily distinguished from other forms of polyarthritis. Prominent features in all forms are a predilection for digital joints and occurrence of osteolysis and ankylosis. Rheumatoid factor is usually absent, and the prognosis appears to be better than that for rheumatoid arthritis. The relationship of HLA-B27 histocompatibility antigen to psoriatic arthritis is indefinite; presence of the antigen predisposes to spondylitis. For most patients, treatment directed at the psoriasis is adequate, especially if it is combined with the administration of nonsteroidal anti-inflammatory drugs.