Psoriatic Arthritis is an autoimmune disease, meaning it occurs when the body’s immune system mistakenly attacks healthy tissue, in this case the joints and skin. The faulty immune response causes inflammation that triggers joint pain, stiffness and swelling. The inflammation can affect the entire body and may lead to permanent joint and tissue damage if it is not treated early and aggressively.

Most people with psoriatic arthritis have skin symptoms before joint symptoms. However, sometimes the joint pain and stiffness strikes first. In some cases, people get psoriatic arthritis without any skin changes.

There are five types of psoriatic arthritis:

• Symmetric psoriatic arthritis. This makes up about 50 percent of psoriatic arthritis cases. Symmetric means it affects joints on both sides of the body at the same time. This type of arthritis is similar to rheumatoid arthritis.
• Asymmetric psoriatic arthritis: This type of PsA appears in 35 percent of people with the condition. It’s called asymmetric because it doesn’t appear in the same joints on both sides of the body.
• Distal psoriatic arthritis: This type causes inflammation and stiffness near the ends of the fingers and toes, along with changes in toenails and fingernails such as pitting, white spots and lifting from the nail bed.
• Spondylitis: Pain and stiffness in the spine and neck are hallmarks of this form of PsA.
• Arthritis mutilans: Although considered the most severe form of PsA, arthritis mutilans affects only 5 percent of people who have the condition. It causes deformities in the small joints at the ends of the fingers and toes, and can destroy them almost completely.

Source: The Arthritis Foundation