Three Screening Tools Help Identify Psoriatic Arthritis

By Lorraine L. Janeczko

July 29, 2014

NEW YORK (Reuters Health) - Three screening tools can help identify psoriatic arthritis (PsA) so patients can receive timely treatment, new research suggests.

As psoriasis typically precedes the onset of PsA, doctors need to be alert for possible arthritis in their psoriasis patients, lead author Dr. Philip J. Mease of the University of Washington and Swedish Medical Center in Seattle wrote in an email to Reuters Health.

All three of the tools his group tested can be used in the office - the Psoriasis and Arthritis Screening Questionnaire (PASQ), the Psoriasis Epidemiology Screening Tool (PEST) and the Toronto PsA Screen ToPAS).

"The longer PsA goes on without adequate treatment, the greater the likelihood that irreversible joint damage and other changes will have occurred by the time appropriate treatment is introduced," Dr. Mease said.

"All three screening tests displayed good sensitivity and specificity in identifying PsA amongst those subsequently confirmed by rheumatologists to have this condition, and in not identifying PsA amongst patients who were subsequently identified as not having it," he said.

Doctors, he continued, need "a questionnaire that has good sensitivity because it is important at the screening stage to get the patient referred for evaluation for possible PsA, and it is better to rule out PsA being present than to miss being able to diagnose the patient who actually has the condition."

In a substudy of the PREPARE trial that estimated the prevalence of PsA in patients in 34 dermatology centers in seven countries, Dr. Mease and colleagues focused on the performance of that study's three screening questionnaires.

As reported online June 25 in Journal of the American Academy of Dermatology, they looked at consecutive patients from the PREPARE study who had been evaluated by dermatologists for plaque psoriasis and randomly assigned to receive one of three questionnaires. The mean age in all three groups was similar, between 49 and 51 years.

The patients were also evaluated by rheumatologists to establish or exclude PsA diagnosis. The researchers assessed questionnaire accuracy by comparing it with that diagnosis. They calculated the sensitivity/specificity and positive/negative predictive values.

Of the 949 patients with psoriasis evaluated by rheumatologists, 285 (30%) were diagnosed with clinical PsA.

The researchers found probable PsA in 45.1%, 43.0%, and 42.9% of patients using PASQ, PEST, and ToPAS, respectively. They also found sensitivities of 0.67, 0.84 and 0.77, respectively; specificities of 0.64, 0.75 and 0.72; positive predictive values of 0.43, 0.60 and 0.54; and negative predictive values of 0.83, 0.91 and 0.88.

While all three tools had acceptable sensitivity and specificity and good negative predictive value, the authors admit to some limitations to their study. These include possible bias, lack of standardized diagnostic criteria, and that not all patients completed all questionnaires.

Dr. Eric M. Ruderman of the Northwestern University Feinberg School of Medicine in Chicago told Reuters Health by email that patients with PsA might not be identified because doctors aren't asking the right questions.

But the diagnosis "is important because the management of a patient with psoriasis and PsA may be different from the management of a patient with psoriasis without arthritis," he wrote.

"All three patient screening tools in this study performed equally well. They identified patients with a high likelihood of having PsA, suggesting that further evaluation by a rheumatologist would be helpful," he wrote. "Equally important, all three screening tools had a high negative predictive value: they identified patients not likely to have PsA, for whom further evaluation was not necessary."

As to which tool to choose, Dr. Ruderman wrote, "Using one of them is more important than worrying about which one is best. Take a look at the screening tools evaluated in this study, decide which one fits most efficiently into your practice flow, and start to use it."

Dr. Lesley Kay, of the Newcastle upon Tyne Hospitals National Health Service Foundation Trust in the U.K., was less enthusiastic about the questionnaires.

"Unfortunately none of the tools is perfect. In particular, many patients with psoriasis have joint pains or back pain for other reasons (most commonly osteoarthritis or mechanical back pain), and the screening tools are not always specific enough to distinguish between these and true inflammatory psoriatic arthritis," she wrote.

Still, Dr. Kay noted, "Raised awareness of the condition amongst dermatologists, which routine intelligent use of these tools may achieve, can lead to earlier diagnosis and better outcomes for patients," she wrote.

Dr. Kay recommends dermatologists who see patients with psoriasis develop good working relationships with their colleagues in rheumatology. "I'd suggest that they discuss with them whether use of these tools locally would improve their referral pathway and patient care," she added.

Pfizer Inc. sponsored the study and was closely involved in conducting it, analyzing the results, and preparing the manuscript. Many of the authors have or had financial relationships with Pfizer.


J Am Acad Dermatol 2014.


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