Diagnosing psoriatic arthritis can be complex. However everyone affected one or more of joint, tendon or spine inflammation. Most of the time patients have, or have had, psoriasis of the skin or nail. It can look different in each person: psoriasis may look different, some may get arthritis, and/or tendon involvement, and/or spine disease as well as possible eye disease or inflammatory bowel disease. As with any rheumatologic disease, we have a set of rules that we follow when we diagnose psoriatic arthritis; these are called criteria.
The criteria includes:
- An examination by the physician determining if the joints are swollen or tender. The most commonly affected joints are the joints of the fingers and/or toes. The doctor will also look for inflammation in the tendons, spine, and swelling of fingers or toes known as “sausage digit”.
- Blood tests to rule out rheumatoid arthritis called a rheumatoid factor and an Anti-cyclic citrullinated peptide antibody test. We would expect these to be negative in psoriatic arthritis. If either or both are positive we would consider the patient to have rheumatoid arthritis.
- Sometimes an X-ray or radiograph of the hands or feet to look for any damage done. Psoriatic arthritis often has a type of damage not seen in other types of rheumatic disease. X-rays will also be useful in checking that there is no additional damage as you progress through treatment.
- A skin examination to look for psoriasis. Some people may just have a patch of scalp psoriasis that never really bothers them that much. The arthritis is the biggest issue.
- A nail examination. The nails will often have ridges and may be growing away from the nail bed.
Your rheumatologist will also take a full history of your symptoms and may perform additional examinations and bloodwork.