There’s no one definitive test.
Psoriatic arthritis—an inflammatory and chronic type of arthritis—affects up to 30 percent of people with psoriasis, according to the National Psoriasis Foundation (NPF). If you have psoriasis, it’s a good idea to be aware of the symptoms of psoriatic arthritis (PsA), because catching it early, if it does develop, may improve treatment outcome.
If you do notice the telltale signs of PsA, such as pain and stiffness in the joints, what’s the next step? Unfortunately, there’s no single test that can diagnose PsA with a yes-or-no answer. Instead, a combination of different exams can help doctors form a PsA diagnosis, according to Leah Anon, MD, rheumatologist at Harlem Health Center and Queens Health Center in New York City.
Here are the factors doctors consider before diagnosing with PsA:
The patient’s symptoms, including when they started, where the stiffness is occurring, and how much it impacts daily life
Personal history of psoriasis
Family history of psoriasis
A physical exam
An X-ray or MRI to check for inflammation or damage to the joints
And blood tests to rule out other conditions.
Other Conditions to Rule Out
Many health conditions can cause joint pain, and psoriatic arthritis can mimic some of them. In particular, doctors need to rule out other types of arthritis like rheumatoid arthritis and gout, according to NPF. Many blood tests used to diagnose PsA are actually meant to rule out these similar conditions.
A blood test that evaluates the “rheumatoid factor” checks for a certain antibody that is typically present in someone with rheumatoid arthritis, but not PsA. (It’s possible, but rare, to have both rheumatoid arthritis and PsA.)
Since PsA usually affects the distal joints close to the nails in the fingers and toes, pain in the toe could be mistaken for gout. To rule out gout, doctors test joint fluid for elevated levels of serum uric acid—a possible sign of gout.
Although symptoms of the different conditions are similar, they have some key differences:
Joint pain caused by gout will usually strike a single joint—often the big toe—very suddenly. Gout causes intense pain.
If there is no swelling in the joints, it is likely osteoarthritis instead of PsA. Another sign of osteoarthritis is pain after activities, whereas PsA causes stiffness and pain in the mornings.
If joint pain is symmetrical and affects the same joints on both sides of the body, it is likely rheumatoid arthritis. PsA joint pain is usually asymmetrical.
PsA also has unique symptoms, such as skin lesions, nail changes, and dactylitis, which is when fingers and toes become swollen and take on a sausage-like appearance.
If you think you have PsA—or any of the related conditions—it’s best to visit your doctor for a professional diagnosis. The sooner you begin treatment for psoriatic arthritis, the more likely you are to avoid permanent joint damage and improve your quality of life.
About psoriatic arthritis. Portland, OR: National Psoriasis Foundation. (Accessed on August 27, 2018 at https://www.psoriasis.org/about-psoriatic-arthritis#symptoms.)
Gout. Portland, OR: National Psoriasis Foundation. (Accessed on August 27, 2018 at https://www.arthritis.org/about-arthritis/types/gout/.)
Psoriatic arthritis. Atlanta, GA: American College of Rheumatology. (Accessed on August 27, 2018 at https://www.rheumatology.org/I-Am-A/Patient-Caregiver/Diseases-Conditions/Psoriatic-Arthritis.)
Psoriatic arthritis. Portland, OR: National Psoriasis Foundation. (Accessed on August 27, 2018 at https://www.psoriasis.org/psoriatic-arthritis.)