CASPAR stands for classification criteria for psoriatic arthritis.

The CASPAR criteria were developed by an international group of rheumatologists in 2006 to help standardize the diagnosis of psoriatic arthritis (PsA). The CASPAR group used results of a large PsA study in 30 clinics in 13 countries to come up with its new criteria.

CASPAR criteria are intended to guide family physicians and specialists in what to look for in making a PsA diagnosis. The aim is to identify people with PsA early so they can be treated before the disease progresses.

PsA causes stiffness, pain, and swelling of joints, tendons, and ligaments. It can also involve other body systems. Symptoms range from relatively mild to fairly severe.

PsA has been underdiagnosed in the past. This is because it has such a wide range of symptoms and its diagnostic criteria weren’t universally agreed upon. It’s estimated that more than half the people with PsA are undiagnosed.

The lack of criteria also made it difficult to select appropriate participants for clinical research in evaluating potential new treatments for PsA.

An earlier classification system proposed in 1973 suggested that PsA and rheumatoid arthritis (RA) were two separate diseases. This criteria described PsA as psoriasis combined with inflammatory arthritis symptoms and usually no blood indicators of RA.

The CASPAR criteria refine this older system to include people with PsA and no psoriasis rash or other arthritis symptoms.

The CASPAR criteria establish a simple point-scoring system for PsA based on symptoms.

First, according to a specialist (rheumatologist or dermatologist), you must have inflammatory arthritis in at least one of the following places:

  • a joint
  • your spine
  • the connective tissue between your tendons or ligament and bone (enthesis)

In addition, you must have at least three points from the following categories, as determined by a specialist:

  • current skin or scalp symptoms of psoriasis (2 points)
  • a history of psoriasis symptoms, but no current symptoms (1 point)
  • a family history of psoriasis and no current or past symptoms (1 point)
  • nail symptoms, such as pitting, detached nails, (onycholysis), or thickening of the skin under your nails (hyperkeratosis) (1 point)
  • a negative blood test for rheumatoid factor (1 point)
  • a swelling of a finger (dactylitis) (1 point)
  • X-ray evidence of new bone growth near a joint (juxtaarticular) (1 point)

The CASPAR system has come into wider use because of its advantages. Some of these are:

  • It’s simple to use.
  • It has high specificity. This means that healthy people who are known not to have PsA will not meet the criteria. The CASPAR criteria have specificity of 98.7 percent.
  • It has good sensitivity. This means the criteria will correctly identify people with PsA. The CASPAR criteria have a sensitivity of 91.4 percent.
  • It includes people who don’t have psoriasis skin symptoms. About 14 to 21 percent of people with PsA develop arthritis symptoms before they have skin symptoms. With prior criteria, these people with PsA might be missed.
  • It includes people who show a low measure of rheumatoid factor. These people with PsA were previously missed under other guidelines.
  • It includes people with dactylitis who don’t have other kinds of arthritis symptoms.

The CASPAR criteria were developed in a large study working from the clinical records of people known to have PsA. There were 588 people with PsA and a control group of 536 people who had RA or other forms of arthritis.

Subsequent studies have shown the usefulness of CASPAR as a diagnostic tool.

  • A 2009 study of 108 Chinese people with PsA found that the CASPAR criteria had a sensitivity of 98.2 percent and a specificity of 99.5 percent. This was much better than previous criteria, according to the study.
  • A 2008 study of 175 people with PsA in a Toronto family medicine clinic showed that the CASPAR criteria had a sensitivity of 100 percent and a specificity of 98.9 percent.
  • A 2012 UK study of 111 people with early PsA and 111 with other types of inflammatory arthritis found that the CASPAR criteria had a sensitivity of 87.4 percent. This compares with 80.2 percent for the previous criteria. Both had a specificity of 99.1 percent.

Like most guidelines, the CASPAR criteria aren’t perfect.

One of the specialists involved in the CASPAR group that produced the criteria, W.J. Taylor, cautioned that there may be other types of data necessary for a diagnosis. Specifically, he said that MRI findings, not mentioned in CASPAR, may be important.

Taylor also noted that CASPAR criteria were derived from studies of people who were already known to have PsA. It may be more limited when evaluating new cases, he said. Further, Taylor said that although the CASPAR criteria were very useful, they didn’t have 100 percent certainty.

It’s very important to diagnose PsA as early as possible. The earlier the diagnosis and treatment, the better the outcome.

PsA is a progressive disease. It’s also variable in onset: It may develop slowly with mild symptoms, or it may suddenly occur in a severe form.

Treating it early and aggressively can slow joint damage and improve quality and length of life. D.D. Gladman, a prominent PsA researcher, noted in her 2016 review of treatment advances that aggressive treatment early enough may be able to prevent joint damage altogether.

Gladman cited two studies that back up this claim. People with PsA in a Toronto clinic who were seen within two years of PsA diagnosis did better than those who came to the clinic having had PsA longer. An Irish study showed that even a 6-month delay in diagnosis and treatment led to a worse outcome.

If you have psoriasis and develop arthritis symptoms, it’s important to see a specialist to check it out. You should also see a doctor if you’re worried about new arthritis symptoms.

The CASPAR criteria were developed to help identify PsA early. You may already be aware of your skin symptoms and your family history. But you’ll want to see a rheumatologist to look for and confirm the signs of inflammatory musculoskeletal disease.

The CASPAR criteria are useful for physicians and specialists. The criteria remove some ambiguities in how PsA is classified and diagnosed.

An international group called GRAPPA, the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis, is working on a version of PsA criteria that can be used by non-experts. The aim is to help more non-specialists diagnose PsA early.

It’s likely that ongoing research will come up with even more specific diagnostic and classification criteria in the future. New, more effective treatments are also available and being improved on.

There are resources available for you now if you have PsA. The National Psoriasis Foundation has information on psoriasis, plus an online support group. The group also provides free assistance for you or a loved one with PsA.