RALEIGH, N.C. – Current screening instruments that are designed to identify the 20%-30% of psoriasis patients who have psoriatic arthritis leave much to be desired, Dr. Jessica A. Walsh asserted at the annual meeting of the Society for Investigative Dermatology.
She asked 189 psoriasis patients who are enrolled in the Utah Psoriasis Initiative to take three of the most popular psoriatic arthritis self-administered screening questionnaires. The tests’ sensitivities and specificities proved markedly lower than previously reported in the instruments’ validation studies.
Moreover, all three tests – the Psoriatic Arthritis Screening and Evaluation (PASE), the Psoriasis Epidemiology Screening Project (PEST), and the Toronto Psoriatic Arthritis Screen (ToPAS) – differentiated only poorly among psoriatic arthritis, other types of arthritis, and fibromyalgia.
And the tests had other weak points: "The instruments were less sensitive in patients with lower psoriatic arthritis disease activity, fewer disease features, and shorter disease duration. This is suboptimal because these instruments were designed to help capture early disease," said Dr. Walsh, a rheumatologist at the University of Utah, Salt Lake City.
She is involved in a project aimed at reducing delays in diagnosis of psoriatic arthritis, an underdiagnosed condition in psoriasis patients. According to a 2011 National Psoriasis Foundation survey, 29% of psoriatic arthritis patients don’t receive their diagnosis until 2 years or more after onset of symptoms. That’s bad news, because early diagnosis and treatment help minimize symptoms, enhance quality of life, and prevent joint damage. Studies show that nearly one-half of psoriatic arthritis patients develop radiographic evidence of erosive damage within 2 years of symptom onset. Treatment can slow that progressive erosion.
All 189 psoriasis patients in Dr. Walsh’s study had musculoskeletal complaints of sufficient magnitude that they were willing to take the three screening tests in order to receive a free rheumatologic evaluation. A total of 137 patients had psoriatic arthritis, and two-thirds of them had already been diagnosed with the disease prior to participation in her study.
The gold standard to which the screening tests were compared was Dr. Walsh’s diagnostic evaluation, which included laboratory testing and imaging as warranted. When there was a discrepancy between any of the screening tests and her diagnosis, as occurred in 138 cases, a second rheumatologist with expertise in psoriatic arthritis was called in as a tiebreaker.
The sensitivities of PACE, PEST, and ToPAS were 68%, 85%, and 75%, respectively. The specificities were worse, at 50%, 45%, and 55%. These are in sharp contrast to previous studies, in which the test sensitivities were 88%-97%, with reported specificities of 79%-95%, she noted.
The frequency of discrepancies between patient responses to specific screening questions and the rheumatologic exam findings varied among the test instruments in a way that caused Dr. Walsh to believe that combining selected questions from each test and, in some cases, modifying the wording might result in a hybrid-screening instrument with improved performance. She plans to test that hypothesis.
Dr. Abrar A. Qureshi, one of the developers of PASE, said he and his coworkers have been thinking along the same lines.
"We’re working on a shorter version of PASE that might work better. Nine of the 15 questions on PASE seem to track well with inflammatory arthritis," commented Dr. Qureshi, vice chairman of the department of dermatology at Brigham and Women’s Hospital, Boston.
The Utah Psoriasis Initiative is funded by the University of Utah department of dermatology. Dr. Walsh reported having no financial conflicts.