Asking the ‘right’ questions may improve diagnosis for PsA

Psoriatic arthritis has an estimated incidence of six per 100,000 and a prevalence of around one to two per 1,000 in the general population.

Saakshi Khattri, MBBS, MD

PsA is often underdiagnosed in both dermatology and rheumatology and leads to poorer patient outcome such as chronic joint damage, increased disability, increased mortality and decreased quality of life as a result of delayed diagnosis. Studies have indicated that 6% to 42% of patients who have psoriasis may develop psoriatic arthritis, according to a study published in BMC Rheumatology.

Of the 7 million adults with psoriasis in United States only 7.4% of these psoriasis patients have been given a diagnosis of PsA, so clearly PsA is being underdiagnosed. In a study conducted in dermatology clinics across USA, of 949 patients with psoriasis, 30% were given the diagnosis of PsA when evaluated by a rheumatologist.

“The biggest thing with psoriasis is the association with psoriatic arthritis,” Saakshi Khattri MBBS, MD, assistant professor of Dermatology, Rheumatology, Internal Medicine at Icahn School of Medicine at Mount Sinai, told Healio. “That can be seen in up to 40% of patients with psoriasis. Psoriatic arthritis is harder to diagnose as, unlike the skin where an erythematous scaly well-defined plaque can be easily seen and a diagnosis of psoriasis easily made, PsA is harder as the symptoms can be insidious. If a joint is swollen and/or tender or X-Rays show erosions, a diagnosis of PsA can be easily made but that is not always the case.”

In a recently published review, authors noted study results indicate certain HLA alleles, such as HLA B*08, B*27 and B*38, were risk factors for the development of PsA. C-reactive protein (hs-CRP), osteoprotegerin, MMP-3, and the C-propeptide of type II collagen to Col2-3/4_{long mono} (CPII to C2C) ratio may be risk factors for PsA. But so far there is no biomarker or test that definitively diagnoses PsA.

To spur research to fill this void, The National Psoriasis Foundation has launched the PsA Diagnosis Project to fund research that results in the development of a diagnostic test for PsA, Khattri said. “Research into biomarkers and the development of a diagnostic test for early detection of PsA has become the area of research focus for the NPF.”

Referring from dermatologist to rheumatologist

To fill an unmet need in screening for PsA, dermatologists need to ask patients whether they have joint pain, ask about morning stiffness, ask about history of dactylitis, look for obvious joint swelling on exam, determine if they have enthesitis according to Khattri. Certain clinical clues point toward an increased risk for PsA and they are, scalp, genital and nail psoriasis.

She also noted that dermatologists should ask patients about arthritic symptoms because if PsA is diagnosed early, patients can be treated sooner to prevent the morbidity associated with delayed diagnosis. Research has shown that a delay of 6 months or more in diagnosis can result in a 4.2 times likelihood of developing erosions and a two times likelihood of developing functional disability.

In a study published in BMC Rheumatology, researchers noted PsA may be more challenging to diagnose than rheumatoid arthritis because general practitioners, primary care physicians and dermatologists are unaware of the indicators of PsA. This results in a delay in referral of patients to a rheumatologist. At times, even with a referral, it can take up to 6 months to see a rheumatologist.

“Given this, dermatologists need to become more comfortable prescribing biologics, Khattri said. If a patient has swollen and tender joints on exam or has said ‘yes’ to a question about PsA, dermatologists should feel comfortable prescribing a biologic that treats both psoriasis and PsA.”

“As dermatologists, we are the first and sometimes the only point of contact that a patient with psoriasis has, so we should be actively asking questions to screen for PsA,” Khattri said.

Advantages and disadvantages of PsA screening tools

Skin lesions often precede symptoms of PsA, thus early diagnosis is essential. Validated screening tools can be useful to increase early diagnosis of PsA in patients with Ps. Several screening tools have been developed for early detection of PsA:

• Psoriasis Epidemiology Screening Tool (PEST), a 5-item questionnaire and a total score of 3 or more is indicative of PsA;
• Toronto Psoriatic Arthritis Screen (ToPAS), a 12 -item questionnaire considered to be highly sensitive and specific;
• Psoriatic Arthritis Screening Evaluation (PASE), designed to help dermatologists identify Ps patients who should be referred to rheumatologist for PsA diagnosis; and
• Psoriasis and Arthritis Screening Questionnaire (PASQ), another screening tool for PsA with 10-item questionnaire.

The disadvantage is that no one screening questionnaire can definitely diagnose PsA and they can be time consuming to administer in a clinic setting. There are many questionnaires available; however, there is no questionnaire that can say a patient definitely has PsA, according to Khattri.

“Questionnaires are also cumbersome,” Khattri said. “There are too many questionnaires; which one do you choose from? What’s the unmet need? The need for a questionnaire that is simple to administer in a dermatologist’s office, which has high sensitivity and specificity.”

CASPAR criteria are currently used to identify patients with PsA and it has shown high sensitivity and specificity for the diagnosis of PsA and is used in PsA clinical trials.

Research needed on cost-savings for PsA screening

In a recent study published in Arthritis Care and Research, researchers looked at the cost-effectiveness of screening psoriatic arthritis in patients with psoriasis in Canada. They found the implementation of screening in patients with psoriasis was expected to represent a savings of $220 million per year and improved quality of life. Compared with no screening, screening tools were more effective.

“Implementing a PsA screening program in Canada would be cost-savings over a 40-year time horizon relative to ‘no screening’,” the authors wrote. “Since the average time in biologic therapy per patient is expected to be reduced, the Canadian Health Care System would save around $220 million per year ($2,000 per patient) while improving quality of life.”

“Studies have shown that a 6-month delay in the diagnosis of PsA has been shown to have an adverse impact on radiographic and functional outcomes, higher symptom burden and poorer quality of life of patients with PsA compared with those with psoriasis alone,” she said. “So, I do think earlier screening can improve quality of life by earlier detection and treatment. As far as saving money goes — one would say yes as earlier detection, lesser disability, deformity and morbidity but I don’t know of any published study that talks about money saved by earlier detection.”

References

• Al Hammadi, A. What is the Classification Criteria for Psoriatic Arthritis (CASPAR)? Available at: https://www.medscape.com/answers/2196539-155439/what-is-the-classification-criteria-for-psoriatic-arthritis-caspar. Accessed: February 25, 2020.
• Haroon M, et al. Ann Rheum Dis. 2015;doi:10.1136/annrheumdis-2013-204858.
• Iragorri N, et al. Arthritis Care Res. 2019;doi:10.1002/acr.24110.
• Mease PJ, et al. J Am Acad Dermatol. 2013;doi:10.1016/j.jaad.2013.07.023.
• National Psoriasis Foundation. The PsA Diagnosis Project. Available at: https://www.psoriasis.org/psa-diagnosis-project. Accessed: March 11, 2020.
• Ocampo V, et al. Version 1. F1000Res. 2019; doi:10.12688/f1000research.19144.1.
• Ogdie A, et al. BMC Rheumatol. 2020; doi:10.1186/s41927-019-0102-7.