Psoriatic arthritis develops in about 30% of patients with psoriasis. Prevalence is increased in patients with AIDS. Risk is increased in patients with human leukocyte antigen B27 (HLA-B27) or some other specific alleles and in family members. Etiology and pathophysiology of psoriatic arthritis 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 rheumatoid arthritis. Rheumatoid nodules are absent. Arthritic remissions tend to be more frequent, rapid, and complete than in rheumatoid arthritis, but progression to chronic arthritis and crippling may occur. There may be arthritis mutilans (destruction of multiple hand joints with telescoping of the digits).
Enthesopathy (inflammation at tendinous insertion into bone—eg, Achilles tendinitis, patellar tendinitis, elbow epicondyles, spinous processes of the vertebrae) can develop and cause pain.
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, particularly when asymmetric or involving the lower spine; 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. However, anticyclic citrullinated peptide antibodies (anti-CCP) are highly specific for rheumatoid arthritis and are not present in psoriatic arthritis.
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 of psoriatic arthritis is directed at controlling skin lesions and at reducing joint inflammation. Drug therapy is similar to that for rheumatoid arthritis, particularly the DMARD methotrexate. Hydroxychloroquine is inconsistently of benefit and may cause exfoliative dermatitis or aggravate underlying psoriasis. Benefit may be gained from nonsteroidal anti-inflammatory drugs, cyclosporine, TNF-alpha antagonists, ustekinumab, secukinumab, ixekizumab, tofacitinib, abatacept, and apremilast (see Biologic agents). TNF-alpha antagonists have been particularly effective. (See also an international task force's 2017 update of recommendations for treating axial spondyloarthritis and peripheral spondyloarthritis, especially psoriatic arthritis.)
Ustekinumab is an interleukin (IL)-12 and IL-23 antagonist. The dosage is 45 mg subcutaneously at weeks 0 and 4 (loading dosages) followed by 45 mg every 12 weeks thereafter. The dosage is 90 mg subcutaneously if the patient weighs > 100 kg. Adverse effects are similar to those of the other biologic agents.
Secukinumab is an IL-17 inhibitor. Secukinumab can be given at a dosage of 150 mg subcutaneously at weeks 0, 1, 2, 3, and 4 and every 4 weeks thereafter. Without the loading (weekly) dosage, secukinumab is given at 150 mg subcutaneously every 4 weeks. If patients continue to have active psoriatic arthritis, a dose of 300 mg should be considered. Secukinumab may be given with or without methotrexate. Adverse effects include urticaria, upper respiratory infections, fungal infections due to Candida, diarrhea, herpes zoster, and inflammatory bowel disease.
Ixekizumab is an IL-17A inhibitor. It is indicated for adults with moderate-to-severe plaque psoriasis who are candidates for systemic therapy or phototherapy as well as for adults with active psoriatic arthritis. It may be given alone or in combination with a conventional DMARD (eg, methotrexate). The dosage is 160 mg subcutaneously (two 80-mg injections) at week 0, followed by 80 mg subcutaneously every 4 weeks. Ixekizumab increases the risk of upper respiratory infections and fungal infections and has also been associated with worsening symptoms of inflammatory bowel disease.
Tofacitinib is an oral Janus kinase (JAK) inhibitor. It is available for adults with active psoriatic arthritis who have had an inadequate response to or who are intolerant of methotrexate or other DMARDs. The dosage is 5 mg orally 2 times a day. The extended-release dosage is 11 mg orally once/day. Potential adverse effects include risk of infection, particularly varicella-zoster virus reactivation, increased creatinine levels, neutropenia, and hyperlipidemia.
Abatacept is a soluble fusion cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) Ig. It is available for adults with active psoriatic arthritis and can be used with or without a nonbiologic DMARD (eg, methotrexate, sulfasalazine, hydroxychloroquine, leflunomide). It may be given as an IV infusion or as a subcutaneous injection. For the IV infusion, the dose is weight adjusted as follows: 500 mg for patients weighing < 60 kg, 750 mg for patients weighing 60 to100 kg, and 1 g for patients weighing > 100 kg. After the initial dosage, abatacept should be given at weeks 2 and 4 and every 4 weeks thereafter. The subcutaneous injection dosage is 125 mg once/week. Adverse effects include pulmonary toxicity, susceptibility to infection, headache, upper respiratory infection, sore throat, and nausea.
Apremilast is a phosphodiesterase-4 inhibitor. The initial dosage is 10 mg orally once/day, titrated to the maintenance dosage of 30 mg orally 2 times a day as tolerated. Adverse effects include diarrhea, nausea, headache, depression, and weight loss.
Psoriatic arthritis is chronic inflammatory spondyloarthropathy 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 distal interphalangeal (DIP) joints more than others.
Diagnose based on clinical findings.
Treat with disease-modifying antirheumatic drugs (DMARDs) and biologic agents.