Psoriatic arthritis is a form of progressive inflammatory arthritis affecting people who have the skin disease psoriasis. An estimated one million people in the United States are thought to have psoriatic arthritis, which affects around one in ten patients with psoriasis. 

There are five varieties of psoriatic arthritis: symmetric (which accounts for approximately half of all psoriatic arthritis cases), asymmetric, distal interphalangeal predominant, spondylitis, and arthritis mutilans. It occurs when the immune system attacks the skins and joints, although the reasons for this happening are not yet clear. However, risk factors include having psoriasis, having HIV, being between 30 and 50 years of age, or a history of strep throat. Family history also seems to play a part, with four out ten patients with psoriatic arthritis having a family history of skin or joint disease.

Symptoms of psoriatic arthritis include nail lesions, inflammation of the fingers and toes, inflammation of the joints, stiffness, painful muscles and tendons, fatigue, conjunctivitis, and eye pain. 

Treatment of psoriatic arthritis focuses on preventing damage to the joints and slowing the progression of the disease. Drug classes commonly prescribed to treat psoriatic arthritis are systemic corticosteroids, plain, nonsteroidal antiinflammatory drugs/NSAIDs, antipsoriatic monoclonal antibodies and others, and anti-rheumatic monoclonal antibody preparations.