CASPAR isn’t the name of a friendly cartoon ghost. It’s a set of rules that can help your doctor figure out if you have psoriatic arthritis.
PsA can be tricky to diagnose. That’s partly because it can have symptoms in common with certain other conditions or types of arthritis, like rheumatoid arthritis or osteoarthritis. So it often takes several tests to spot signs of PsA and rule other health problems out.
But the CASPAR criteria might help your doctor make the final call. Here’s what you need to know.
Why Is It Called CASPAR?
The term CASPAR comes from the phrase “classification criteria for psoriatic arthritis.” In 2006, experts proposed this set of diagnostic rules based on an international study, which looked at over 580 people with psoriatic arthritis and more than 530 people with other types of inflammatory arthritis.
The CASPAR criteria became the first set of rules to classify psoriatic arthritis that experts generally agreed on.
How Do Doctors Use the CASPAR Criteria?
CASPAR can help doctors diagnose psoriatic arthritis. But they can only use this set of guiding rules if you show signs of an inflammation-causing disease related to the muscles and skeleton, like:
Peripheral arthritis. This usually affects the large joints in your arms and legs, like your elbows, wrists, knees, and ankles.
Axial arthritis. This mainly affects your spine and the joints that connect the bottom of your backbone to your pelvis.
Enthesitis. This condition happens when an enthesis – the site where a tendon or ligament connects to a bone – becomes inflamed. Your body has over 100 of these sites.
Your doctor then uses the CASPAR criteria like this: They go through a list of signs, which each have different point values. If you end up with a total of three or more points, it means you could have psoriatic arthritis.
Here are the symptoms and their point values.
Skin psoriasis that:
- Is currently on your body (2 points), or
- Used to be on your body (1 point), or
- Affects a close relative -- like a parent -- but not you (1 point)
Nail symptoms like these (1 point):
- Small dents in the plates
- Thickening nails
- Nails separate from the skin underneath
Dactylitis (1 point). This means inflammation or swelling of a whole finger or toe. You could have it now or in the past, as long as an arthritis doctor (a rheumatologist) diagnosed you with it.
Negative test result for rheumatoid factor (1 point). This means a blood test showed you had a low level of an antibody called rheumatoid factor (RF). Doctors expect this test result to be “negative” – meaning a low level of RF – in people with psoriatic arthritis. On the other hand, a “positive result” – meaning a high level of RF – could be a sign of rheumatoid arthritis.
Imaging tests show signs of new bone forming due to joint inflammation (1 point). X-rays and CT scans are examples of imaging tests that can spot signs like this.
What Else Helps Doctors Diagnose Psoriatic Arthritis?
If your doctor uses the CASPAR criteria, they’ll also ask you about your symptoms and give you a physical exam. They’ll check your joints for pain, stiffness, and swelling. They might have you do simple activities to watch how well you move.
They may test your blood for signs of inflammation, too.
If the doctor diagnoses you with psoriatic arthritis, treatment can ease your symptoms and help keep the disease in check.