Psoriatic arthritis (PsA) is a joint condition or arthritis that affects people with the skin condition known as psoriasis. PsA occurs when the body’s immune system attacks healthy tissue.
Research has not determined the exact cause, but approximately 40 percent of people who have the disease also have a close family member with either psoriasis or arthritis. This suggests that the condition may be hereditary. Scientists have also discovered genetic markers that are related to PsA.
There are five basic types of PsA:
Asymmetric psoriatic arthritis
Between 30 and 50 percent of people with PsA develop this condition first. It is characterized by random joint involvement of the extremities on either side of the body, such as right toes or left fingers.
Symmetric psoriatic arthritis
This is the most common type of PsA. It is characterized by pain and swelling in the joints of the extremities on both sides of the body. Asymmetric PsA often develops into this form over time.
Distal interphalangeal predominant psoriatic arthritis
People with this type of PsA have pain and swelling, primarily in the joints closest to the fingernails and toenails. The nails may also show pitting, splitting or other types of degeneration.
This is a more destructive and painful type of the disease which accounts for approximately 5 percent of all PsA cases. It can cause inflammation where tendons and ligaments attach to the bones, which is known as enthesitis. This can cause pain at the back of the heel, on the sole of the foot or around the elbows. Arthritis mutilans may also result in the resorption of the small bones in the fingers and toes.
This type of PsA can result in inflammation between the joints of the vertebrae in the spine and between the spine and the pelvis. It causes pain in the back or neck and may lead to difficulty bending.
There is no cure for PsA. Treatment typically focuses on controlling inflammation in the joints to reduce pain and limit disability.