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Psoriatic arthritis is a spondyloarthropathy and chronic inflammatory arthritis that occurs in people with psoriasis of the skin or nails. The arthritis is often asymmetric, and some forms involve the distal interphalangeal joints. Diagnosis is clinical. Treatment is usually similar to that of RA but can also involve phototherapy.
Psoriatic arthritis develops in about 30% of patients with psoriasis. Prevalence is increased in patients with AIDS. Risk of some involvement is increased in patients with HLA-B27 or some other specific alleles and in family members. Etiology and pathophysiology are unknown.
Psoriasis of the skin or nails may precede or follow joint involvement. Severity of the joint and skin disease is often discordant. Also, skin lesions may be hidden in the scalp, gluteal folds, or umbilicus and go unrecognized by the patient.
The distal interphalangeal (DIP) joints of fingers and toes are especially affected. Asymmetric involvement of large and small joints, including the sacroiliacs and spine, is common. Joint and skin symptoms may lessen or worsen simultaneously. Inflammation of the fingers, toes, or both may lead to sausage-shaped deformities, which are not present in patients with RA. Rheumatoid nodules are absent. Arthritic remissions tend to be more frequent, rapid, and complete than in RA, but progression to chronic arthritis and crippling may occur. There may be arthritis mutilans (destruction of multiple hand joints with telescoping of the digits).
Back pain may be present. It is often accompanied by asymmetric syndesmophytes of the spine.
Psoriatic arthritis should be suspected in patients with both psoriasis and arthritis. Because psoriasis may be overlooked or hidden or develop only after arthritis occurs, psoriatic arthritis should be considered in any patient with seronegative inflammatory arthritis; these patients should be examined for psoriasis and nail pitting and should be questioned about a family history of psoriasis. Patients suspected of having psoriatic arthritis should be tested for RF. Occasionally, RF test results can be positive as may anticyclic citrullinated peptide antibody (anti-CCP) results.
Psoriatic arthritis is diagnosed clinically and by excluding other disorders that can cause such similar manifestations. X-ray findings common in psoriatic arthritis include distal interphalangeal joint involvement; resorption of terminal phalanges; arthritis mutilans; and extensive destruction, proliferative bone reaction, a sausage-like appearance to digits, and dislocation of large and small joints.
Treatment is directed at controlling skin lesions (see Treatment) and at reducing joint inflammation. Drug therapy is similar to that for RA, particularly methotrexate. Hydroxychloroquine is inconsistently of benefit and may cause exfoliative dermatitis or aggravate underlying psoriasis. Benefit may be gained from NSAIDs, cyclosporine, and TNF-α antagonists (see Other agents); TNF-α antagonists have been particularly effective.
Phototherapy using long-wave psoralen plus ultraviolet A (PUVA) combined with oral methoxsalen 600 mcg/kg po 2 h before PUVA twice/wk seems to be highly effective for psoriatic lesions and somewhat effective for peripheral arthritis, but not for spine involvement.
Ustekinumab is an IL-12 and IL-23 antagonist. The dose is 45 mg IM at wk 0 and 4 (loading doses) followed by 45 mg every 12 wk thereafter. The dose is 90 mg IM if the patient weighs > 100 kg. Adverse effects are similar to those of the other biologic agents.
Apremilast is a phosphodiesterase-4 inhibitor. The initial dose is 10 mg po once/day, titrated to the maintenance dose of 30 mg bid as tolerated. Adverse effects include diarrhea, nausea, headache, depression, and weight loss.
Psoriatic arthritis is chronic inflammatory arthritis that occurs in patients with psoriasis; however, psoriasis may be mild or overlooked or may have not yet developed.
Arthritis is commonly asymmetric, involves large and small joints (including axial joints), and typically affects the finger and toe DIP joints more than others.
Diagnose based on clinical findings.
Treat with drug therapy that is similar to that of RA and sometimes with phototherapy.
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