In severe forms, psoriatic arthritis may progress to arthritis mutilans which on X-ray gives a "pencil-in-cup" appearance.Because prolonged inflammation can lead to joint damage, early diagnosis and treatment to slow or prevent joint damage is recommended. Causes
The exact causes are not yet known, however silica dust exposure has been identified in Australia and a number of genetic associations have been identified in a genome-wide association study of psoriasis and psoriatic arthritis including HLA-B27. Diagnosis
There is no definitive test to diagnose psoriatic arthritis. Symptoms of psoriatic arthritis may closely resemble other diseases, including rheumatoid arthritis. A rheumatologist (a physician specializing in autoimmune diseases) may use physical examinations, health history, blood tests and x-rays to accurately diagnose psoriatic arthritis. Factors that contribute to a diagnosis of psoriatic arthritis include the following:

Psoriasis in the patient, or a family history of psoriasis or psoriatic arthritis. A negative test result for rheumatoid factor, a blood factor associated with rheumatoid arthritis. Arthritis symptoms in the distal Interphalangeal articulations of hand (the joints closest to the tips of the fingers). This is not typical of rheumatoid arthritis. Ridging or pitting of fingernails or toenails (onycholysis), which is associated with psoriasis and psoriatic arthritis. Radiologic images demonstrating degenerative joint changes.Other symptoms that are more typical of psoriatic arthritis than other forms of arthritis include enthesitis (inflammation in the Achilles tendon (at the back of the heel) or the plantar fascia (bottom of the feet)), and dactylitis (sausage-like swelling of the fingers or toes).
Rather than just reducing pain and inflammation, this class of drugs helps limit the amount of joint damage that occurs in psoriatic arthritis. Most DMARDs act slowly and may take weeks or even months to take full effect. Drugs such as methotrexate or leflunomide are commonly prescribed; other DMARDS used to treat psoriatic arthritis include cyclosporin, azathioprine, and sulfasalazine. According to a recent Cochrane review, low dose oral methotrexate was slightly more effective than placebos. Immunosuppressant drugs can also reduce psoriasis skin symptoms but can lead to liver and kidney problems and an increased risk of serious infection. Biological response modifiers
A new class of therapeutics called biological response modifiers or biologics has been developed using recombinant DNA technology. Biologic medications are derived from living cells cultured in a laboratory. Unlike traditional DMARDS that affect the entire immune system, biologics target specific parts of the immune system. They are given by injection or intravenous (IV) infusion. Biologics prescribed for psoriatic arthritis are TNF-α inhibitors, including infliximab, etanercept, golimumab, certolizumab pegol and adalimumab, as well as the IL-12/IL-23 inhibitor ustekinumab, and the IL-17a inhibitor secukinumab. Recently, the Jak inhibitor, tofacitinib (Xeljanz), was approved for the use in active psoriatic arthritis.Biologics may increase the risk of minor and serious infections. More rarely, they may be associated with nervous system disorders, blood disorders or certain types of cancer. Phosphodiesterase-4 inhibitors
A first-in-class treatment option for the management of psoriatic arthritis is apremilast; a small molecule phosphodiesterase-4 inhibitor approved for use by the FDA in 2014.