A. Rheumatoid factor is seen in fewer than 10% of PA patients.
B. Polyclonal hypergammaglobulinemia is occasionally present.
C. Serum complement in patients with PA tends to be higher than normal; however, this finding is of no diagnostic significance. Theoretically, elevated synovial fluid complement levels might distinguish PA from RA. Such measurements are frequently subnormal in RA.
E. The erythrocyte sedimentation rate and other acute-phase reactants are elevated and parallel the activity of the arthritis.
F. Test results for antinuclear factors are usually negative.
G. Radiographic features considered classic for PA are destructive lesions involving predominantly the DIP joints of fingers and the IP joints of the toes. Bony ankylosis of the DIP joints of the hand and toes, along with bony proliferation of the base of the distal phalanx, and resorption of the tufts of the distal phalanges of hands and feet are also commonly seen. Other classic features are fluffy periostitis of large joints, "pencil-in-cup" appearance of DIP joints, an asymmetric joint pattern, and gross destruction of isolated small joints. Changes in the spine and sacroiliac (SI) joints may be similar to those seen in ankylosing spondylitis, but SI joint changes in PA are often unilateral, and syndesmophytes can sometimes be distinguished from those of ankylosing spondylitis.
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