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Key Features

Essentials of Diagnosis

  • Psoriasis precedes arthritis in 80% of cases

  • Arthritis usually asymmetric, with "sausage" appearance of fingers and toes; polyarthritis that resembles rheumatoid arthritis also occurs

  • Sacroiliac joint involvement common

  • Radiographic findings

    • Osteolysis

    • Pencil-in-cup deformity

    • Relative lack of osteoporosis

    • Bony ankylosis

    • Asymmetric sacroiliitis

    • Atypical syndesmophytes

General Considerations

  • Although psoriasis usually precedes the onset of arthritis, arthritis precedes (by up to 2 years) or occurs simultaneously with the skin disease in approximately 20% of cases

  • The patterns or subsets of psoriatic arthritis include the following:

    • A symmetric polyarthritis that resembles rheumatoid arthritis; usually, fewer joints are involved than in rheumatoid arthritis

    • An oligoarticular form that may lead to considerable destruction of the affected joints

    • A pattern of disease in which the distal interphalangeal (DIP) joints are primarily affected

      • Early, this may be monarticular

      • Joint involvement is often asymmetric

      • Pitting of the nails and onycholysis frequently accompany DIP involvement

    • A severe deforming arthritis (arthritis mutilans) in which osteolysis is marked

    • A spondylitic form in which sacroiliitis and spinal involvement predominate; 50% of these patients are HLA-B27-positive

Clinical Findings

  • Arthritis is at least five times more common in patients with severe skin disease than in those with only mild skin findings

  • Occasionally, however, patients may have a single patch of psoriasis (typically hidden in the scalp, gluteal cleft, or umbilicus) and are unaware of its presence

  • Psoriatic lesions may have cleared when arthritis appears; in such cases, the history is most useful in diagnosing previously unexplained cases of mono- or oligoarthritis

  • Nail pitting is sometimes a clue

  • "Sausage" swelling of one or more digits is a common manifestation of enthesopathy in psoriatic arthritis

Diagnosis

Laboratory Findings

  • Elevated erythrocyte sedimentation rate

  • Rheumatoid factor and anti-CCP antibodies are not present

  • Uric acid levels

    • May be high, reflecting the active turnover of skin affected by psoriasis

    • There is a correlation between the extent of psoriatic involvement and the level of uric acid, but gout is no more common than in patients without psoriasis

  • Desquamation of the skin may also reduce iron stores

Imaging

  • Radiographic findings are most helpful in distinguishing the disease from other forms of arthritis

  • MRI is more sensitive than plain radiographs in detecting axial abnormalities, especially in the first few years of disease onset

  • Ultrasonography and MRI are more sensitive than conventional radiographs in detecting peripheral arthritis, enthesitis, and dactylitis

Treatment

  • Nonsteroidal anti-inflammatory drugs (NSAIDs) are usually sufficient for mild cases

  • Methotrexate (7.5–20 mg orally once a week)

    • Considered the drug of choice for patients with peripheral arthritis who have not responded to NSAIDs

    • Can improve both the cutaneous and arthritic manifestations

    • Not effective for axial arthritis

  • TNF inhibitor (at doses similar to the treatment of ankylosing spondylitis)

    • Usually effective ...

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