Psoriatic Arthritis Diagnosis
Diagnosing psoriatic arthritis can be a tricky process because its symptoms frequently mimic those of other forms of inflammatory arthritis, such as rheumatoid arthritis (RA) and gout. It can also be confused with osteoarthritis (OA), the most common form of arthritis.
For a proper diagnosis, the primary care doctor will likely provide a referral to a rheumatologist, a type of doctor who specializes in arthritis and musculoskeletal diseases. A diagnosis is based on many things, including a thorough medical history and the results of a physical examination and medical tests.
Because certain conditions can be inherited, the doctor will ask questions about the health history of the patient and his or her relatives.
Additional information needed to help diagnose PsA includes:
- A description of the symptoms
- Details about when and how the pain or other symptoms began
- Location of the pain, stiffness or other symptoms
- How the symptoms affect the patient's daily life
- Details about medical problems that could be causing these symptoms and a list of currently used medications
The rheumatologist will perform a physical exam, looking for swelling and inflammation of the joints. He’ll also check for signs of psoriasis on the skin or abnormalities on fingernails and toenails. Keep in mind that psoriasis isn’t always readily visible. It can hide on the scalp, behind the ears, in the belly button and in the groove between the buttocks.
The doctor may order X-rays to detect changes to the bones or joints. Blood tests will be done to check for signs of inflammation. They include C-reactive protein and rheumatoid factor (RF). People with PsA are almost always RF-negative. If blood tests are positive for rheumatoid factor, the doctor should suspect RA first.
A blood test to measure the sedimentation or "sed" rate is often done. The higher the “sed rate,” the greater the level of inflammation in the body. The doctor may also test joint fluid to exclude gout or infectious arthritis.
Because psoriatic arthritis can be tricky to diagnose, people sometimes are initially told they have another form of arthritis only to find out later they have psoriatic arthritis.
Ruling Out Other Conditions
The symptoms of psoriatic arthritis can mimic other conditions. Common misdiagnoses include osteoarthritis, rheumatoid arthritis and gout. Below are some tips to help avoid a psoriatic arthritis misdiagnosis.
- If a single joint becomes swollen and extremely painful almost overnight, it’s probably gout. Gout pain comes on rapidly and is intense.
- If there is little or no joint swelling, osteoarthritis is the most likely diagnosis. Osteoarthritis pain tends to be felt after activity.
- If joint pain affects the same joint on both sides of the body (is symmetrical), it could be RA. Joint pain in PsA is usually asymmetrical, meaning it's felt on one side of the body. For example, if one knee is affected, the other likely is not.
If joint pain is worse for more than a few minutes in the morning, or after inactivity, consider PsA or RA.
If swelling involves the full length of the fingers or toes, think PsA. This condition is called dactylitis, or “sausage fingers.”
If there are psoriasis symptoms and nail pitting first, followed by joint pain, PsA is likely the culprit, particularly if there is joint swelling. A person can have psoriasis and a form of arthritis that isn’t PsA.