Psoriatic arthritis is a chronic inflammatory disease that affects both the skin and joints. It is a form of arthritis that occurs in people who have psoriasis, which is a common skin condition characterized by red patches covered with silvery scales. Psoriatic arthritis causes swelling and pain in the joints, as well as inflammation in tendons and ligaments. It can also cause changes to the spine that resemble those seen in people with rheumatoid arthritis or other forms of psoriasis. The exact cause of psoriatic arthritis is unknown, but it is believed to involve a combination of genetic and environmental factors. Treatment typically involves medications such as nonsteroidal anti-inflammatory drugs (NSAIDs), corticosteroids, or biologics that target specific immune system components involved in the disease process.