There are three main varieties of psoriatic arthritis (an inflammatory arthritis affecting 5 to 42% of patients with psoriasis): asymmetric inflammatory arthritis, symmetric arthritis , and psoriatic spondylitis. The pathology is similar to that seen in RA (early neutrophil and later monocytic synovial infiltration). There are no characteristic laboratory abnormalities in patients with psoriatic arthritis, but radiographs, if they reveal features unique to this disease relative to RA, may be diagnostically helpful. Such special features include the pencil-in-cup appearance of the distal terminal phalanx due to cuplike erosions. and bony proliferation with tapering of the proximal phalanx; proliferation of the bone near osseous erosions, terminal phalyngeal osteolyis, bone proliferation and perios­titis, and telescoping of one bone into another (opera-glass deformity). Inflammation of the tendons and ligaments (ethesopathy) is also characteristic. Nonsteroidal anti-inflam­matory agents are the therapeutic mainstays; sulfasalazine or methotrexate is often required in difficult cases.