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For further information, see CMDT Part 20-32: Psoriatic Arthritis
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Essentials of Diagnosis
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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
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General Considerations
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Although psoriasis usually precedes the onset of arthritis, arthritis may precede skin disease by up to 2 years or occur simultaneously 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
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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 of one or more digits is a common manifestation of enthesopathy in psoriatic arthritis
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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
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Radiographic findings are most helpful in distinguishing the disease from other forms of arthritis
MRI is more sensitive than conventional 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
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A TNF inhibitor is recommended as first-line agent
If a TNF inhibitor is contraindicated or not tolerated
Methotrexate (7.5–20 mg orally once a week)
Other non-biologic agents, such as leflunomide, sulfasalazine, cyclosporine, or apremilast
Monoclonal antibodies may be used ...