Musculoskeletal Imaging

Psoriatic arthritis

a seronegative spondyloarthropathy occurring in some patients with psoriasis. Five broad clinical varieties of psoriatic arthritis have been recognized:

  • polyarthritis characterized by distal interphalangeal joint involvement;

  • a deforming type of arthritis characterized by widespread ankylosis and occasionally arthritis mutilans;

  • a symmetric seronegative polyarthritis simulating rheumatoid arthritis but without rheumatoid factor;

  • monoarthritis or asymmetric oligoarthritis; and

  • sacroiliitis and spondylitis resembling ankylosing spondylitis.

    The articular disease may be monoarticular, pauciarticular or polyarticular in its distribution, and virtually any joint can be affected. In some patients, low back complaints predominate because of involvement of the spine and the sacroiliac joints. Prominent soft tissue swelling about involved joints, which may affect an entire digit (sausage digit), sometimes occurs. The histocompatibility antigen HLA-B27 is frequently present in patients with psoriasis and sacroiliitis. Classic radiographic features of psoriatic arthritis are listed in Table 1 (Fig.1) (Fig.2).

    Psoriatic arthritis, Table 1. Characteristics of psoriatic arthritis.

    Involvement of synovial and cartilaginous joints and entheses
    Asymmetric distribution more common than symmetric distribution
    Involvement of interphalangeal joints of the hands and feet
    Sacroiliitis and spondylitis with paravertebral ossification
    Bone erosion witih adjacent proliferation
    Intraarticular bone ankylosis
    Destruction of phalangeal tufts

    Among the abnormalities seen in psoriatic arthritis are soft tissue swelling, joint space narrowing or widening, prominent bone erosion, striking bone proliferation, and periostitis in the metaphyses and diaphyses (leading to ivory phalanx, intraarticular bone fusion in large joints, resorption of the tufts of the distal phalanges and malalignment and subluxation of joints (opera glass hand).

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    Fig.1

    PA radiograph of the hand demonstrates soft tissue swelling of the third finger, periostitis (arrows) and erosions at the margin of the distal interphalangeal joint.
    Psoriatic arthritis, Fig.1
    Psoriatic arthritis, Fig.2