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Up to 30% of psoriasis patients will develop psoriatic arthritis. Studies show that a proportion of patients in clinical care have undiagnosed PsA.
Many screening questionnaires for psoriatic arthritis are available, but there is little evidence comparing them, even though guidelines recommend that psoriasis patients should receive annual screening to identify psoriatic arthritis. Often, signs of psoriatic arthritis go undetected for years, and psoriasis patients may miss out on the opportunity to begin early treatment for psoriatic arthritis.
Up to 30% of psoriasis patients go on to develop psoriatic arthritis. Many studies have identified that a proportion of patients under active follow-up in primary care or secondary dermatology clinics for psoriasis have undiagnosed psoriatic arthritis.
Studies show that screening tests can accurately identify people with psoriasis who also show symptoms of psoriatic arthritis. Three such diagnostic questionnaires - the Psoriasis and Arthritis Screening Questionnaire (PASQ), Psoriasis Epidemiology Screening Tool (PEST) and Toronto Psoriatic Arthritis Screen (ToPAS) - have been compared with rheumatologist assessment of patients with psoriasis.
In a study of 949 consecutive, unselected patients with psoriasis who were initially evaluated by dermatologists for plaque psoriasis, the patients were randomized to receive one of these three questionnaires.1 The patients from dermatology clinics in the United States, Canada and Europe, were also evaluated by a rheumatologist, who used a physical examination and blood tests to determine whether a patient had psoriatic arthritis.
After rheumatologist evaluation, 285 patients (30%) received a clinical diagnosis of psoriatic arthritis. All three screening tests were “acceptable and generally similar,” the researchers stated. The success rates for predicting who had psoriatic arthritis ranged from 43-60% among the three tests. The tests were better at determining which patients did not have psoriatic arthritis -- PEST correctly predicted psoriatic arthritis 91% of the time, PASQ 83%, and ToPas 88%.
A new study compared PEST to the proposed CONTEST questionnaire, which was developed to identify patients with psoriasis who have undiagnosed psoriatic arthritis.2 CONTEST was developed using the most discriminative items from existing questionnaires to identify increasing positive predictive value with positivity on multiple questionnaires in secondary care.
The study included a random sample of adult patients with psoriasis and no diagnosis of arthritis who were identified from five general practice clinics in Yorkshire, United Kingdom. Patients completed both questionnaires and assessments by a dermatologist and rheumatologist. The rheumatologist made the diagnosis of psoriatic arthritis.
The study recruited 191 patients, and 169 patients were confirmed to have current or previous psoriasis. Using physician diagnosis, 17 patients (10.1%) were found to have previously undiagnosed psoriatic arthritis, 90 patients (53.3%) had another musculoskeletal complaint, and 62 patients (36.7%) had no musculoskeletal problems.
The questionnaires showed a significant ability to identify psoriatic arthritis, with the CONTEST questionnaire at a slightly higher rate than PEST. There was no significant difference between the questionnaires in their ability to identify psoriatic arthritis, “but a much larger study would be needed to identify a significant difference in the questionnaires' sensitivities and specificities,” the researchers stated.
They noted that the population in this study was drawn from primary care practices, in comparison with their previous study of CONTEST, in which patients were recruited from dermatology outpatient clinics.
A high proportion of false positives were reported in patients who had osteoarthritis or other musculoskeletal complaints and typical symptoms of psoriatic arthritis on these screening questionnaires, including answering positive to a question about dactylitis. In addition, a significant number of patients without psoriatic arthritis identified poor function or quality of life. Poor quality of life would be expected in patients with significant limitations due to the other musculoskeletal complaints, the researchers noted. PsAQoL, which was developed specifically for psoriatic arthritis patients, may be more relevant to patients with chronic psoriasis or other musculoskeletal disorders. The most pertinent questions in the PsAQOL relate to tiredness, depression or lifestyle limitation, they stated.
About 10% of the patients with psoriasis had previously been diagnosed with psoriatic arthritis, and an additional 10% were found to have psoriatic arthritis on examination. The overall 18.1% prevalence of psoriatic arthritis is slightly lower than the 30% reported in large secondary care cohorts, but is similar to a recent meta-analysis that found an overall prevalence of 15.5%.3 “Our estimate of 18.1% is also likely to be an overestimate, as people with musculoskeletal symptoms are presumably more likely to respond and attend for examination, creating a selection bias,” the researchers stated.
The misdiagnosis rate for psoriasis in the study was about 10%. Alternative diagnoses included seborrhoeic dermatitis, eczema, actinic keratosis and ichthyosis vulgaris. There are also likely to be some patients who have psoriasis, but have not been identified yet, perhaps because they have never consulted a physician or because they have not had the correct diagnosis made by their primary care physician, they stated.
In conclusion, the researchers stated that “this study demonstrates the significant ability of the PEST and CONTEST screening questionnaires to identify psoriatic arthritis in a primary care population, but no significant improvement in performance has been shown by the new instruments. Low specificity remains a problem for these tools in clinical practice, but the use of these questionnaires to screen for musculoskeletal disorders in patients with psoriasis should continue. Inappropriate referrals to rheumatology can be minimized by a brief clinical assessment prior to referral, and the use of these screening questionnaires will help identify cases of psoriatic arthritis that currently remain undiagnosed.”
The problem of low specificity still remains with these screening tools, and the new CONTEST tool does not really improve on this. Psoriatic arthritis is a heterogeneous disease, and “developing a questionnaire to identify cases precisely, while excluding other causes of musculoskeletal pain, seems problematic,” the researchers stated. “Perhaps the existing tools cannot be improved upon and the deficiencies should be accepted and acknowledged. The other cases of musculoskeletal pain clearly have an impact on the patient, and perhaps need review by a rheumatologist just as much as those with psoriatic arthritis.”
They suggest that although many patient-reported screening questionnaires for psoriatic arthritis have been developed, they have not been widely adopted in clinical practice and the optimal screening tool has yet to be established.