Arthritis, Psoriatic

Essentials of Diagnosis

• Psoriasis precedes arthritis in 80% of cases

• Arthritis usually asymmetric, with "sausage" appearance of fingers and toes (dactylitis); polyarthritis that may resemble rheumatoid arthritis

• 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 oligoarthritis 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) with osteolysis

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

• Arthritis is at least five times more common in patients with severe psoriatic 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, or dactylitis, of one or more digits is a common manifestation of enthesopathy in psoriatic arthritis

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

• A TNF inhibitor biologic agent is recommended as first-line agent

• If TNF inhibitor is contraindicated or not tolerated, methotrexate (or other oral small molecule agent, such as leflunomide, sulfasalazine, cyclosporine, or apremilast) may be effective

• Patients who do not respond to TNF inhibitors or oral small molecule agents can be treated with

  • Ustekinumab, a monoclonal antibody that inhibits IL-12 and IL-23 or

  • Secukinumab or ixekizumab, which inhibit IL-17

• Tofacitanib (Jak-stat inhibitor) and abatacept (CTLA4 inhibitor) may be options when other therapies fail

• Corticosteroids are less effective in psoriatic arthritis than in other forms of inflammatory arthritis and may precipitate pustular psoriasis during tapers