A quarter of people with skin psoriasis (inflammation and thickening of parts of the skin) can get a form of arthritis called psoriatic arthritis. Occasionally the arthritis can start before the skin condition.
The main pathology in psoriatic arthritis is inflammation at the interface where ligaments or tendons insert into bone. Inflammation of this area is called enthesitis. This often results in pain and swelling of the nearby joint. When the tendons in the fingers that insert near the nailbed are involved it can cause abnormality in the nail.
Psoriatic arthritis can affect just one area, a few joint and tendon areas or it can involve many parts of the body all at once. An inflammatory condition of the eye called iritis and inflammatory bowel disease often co-exist and are thought to be part of the same disease process.
The main recognised risk factors are a personal or family history of skin psoriasis. About 40% of people with psoriatic arthritis will have a family member with skin psoriasis or psoriatic arthritis. Other risk factors include obesity and smoking. Anxiety and depression are also very common co-morbid conditions.
Treatment depends on the severity of the disease and can range from joint injection, anti-inflammatories and disease modifying medication such as methotrexate, salazopyrin or leflunomide. In the worst cases - anti-TNF biological disease modifying drugs such as adalimumab and etanercept can be used. There are some other treatment options such as apremilast, ustekinumumab and secukinumab available overseas but not yet available in New Zealand. In those who are overweight, weight-loss may improve the effectiveness of medical therapy.