IS Case 366: Psoriatic arthritis
2009 URMC Imaging Sciences
Publication Date: 2010-03-02
Radiographs of the hands demonstrate marginal erosions and joint space narrowing involving the PIP and DIP joints of the left ring finger. In addition, there is fusiform soft tissue swelling of the affected digit. Mineralization is normal. There is a marginal erosion at the base of proximal phalanx of the right index finger as well. The remainder of the fingers as well as both wrists appear unremarkable.
Psoriatic arthritis (PsA) is seen in ~15% of patients with psoriasis. In ~85% of patients with psoriasis, skin lesions manifest first. In 10%, arthritis is the presenting symptom/finding. Age at onset is usually 30-45 years and there is no sex predilection. Psoriatic is one of the seronegative (i.e., rheumatoid factor negative) spondyloarthropathies, along with reactive arthritis (previously Reiter's disease), ankylosing spondylitis, and enteropathic arthropathy. Patients are typically HLA-B27 positive and will have elevated CRP and ESR levels.
The hands, feet, SI joints, and spine are the most commonly involved joints. In the hands, the DIP joints are most commonly affected. PsA is typically an asymmetric oligoarthritis, as in our case. Other patterns include symmetric polyarthritis, mimicking rheumatoid arthritis (RA), arthritis of the SI joints and spine, and rapidly progressive and deforming "arthritis mutilans". These various forms can coexist in a single patient. The underlying process is comprised of synovitis, osteitis and enthesitis. Radiographic features of involved digits include smooth, fusiform soft tissue swelling and marginal joint erosions. The wrists are typically spared. Bone demineralization is not a major feature, in contradistinction to RA. Perostitis and periarticular new bone formation are nonspecific but characteristic features. Erosions in PsA are aggressive, lacking the sclerotic rim characteristic of gout. Tuft resorption (acroosteolysis) may be seen. Buzz words include the "pencil-in-cup" deformity "arthritis mutilans" and "sausage digit". Findings in the axial skeleton are not discussed here.
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