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Psoriatic arthritis (PsA) is a highly heterogeneous disease that can be difficult to diagnose, which is important because a of just 6 months has been shown to increase risks of joint erosions, damage, and disability. Yet in , 41% of patients in a dermatology clinic who had never been diagnosed with PsA were found to have the disease when screened with medical history, physical examination, and laboratory testing.

"Currently, we are missing a lot of patients," said Joseph Merola, MD, of Brigham and Women's Hospital in Boston in a webcast sponsored by the Autoimmune Learning Network.

Screening and Referral

Multiple challenges exist in the diagnosis of PsA, according to Merola. Along with the heterogeneity, these include the fact that it's a clinical diagnosis -- there is no diagnostic test -- and there is relatively limited awareness of PsA among non-rheumatologists, he said.

Therefore, a variety of validated screening tools have been developed that typically are used in the primary care or dermatology settings. One of these is the five-question . If responses to three or more of the questions are positive, the patient should be referred to a rheumatologist:

1. Have you ever had a swollen joint or joints?
2. Has a doctor ever told you that you have arthritis?
3. Do you fingernails or toenails have holes or pits?
4. Have you ever had pain in your heel?
5. Have you had a finger or toe that was completely swollen and painful for no apparent reason?

Another tool that can be used to evaluate whether the patient should be referred, or if a patient on treatment considers the current state of disease as acceptable or not, is the , which rates multiple aspects of disease with 12 questions, including pain, fatigue, work and/or leisure activities, sleep disturbances, coping, anxiety, social participation, and depression. Ratings range from "none" to "extreme," with final scores being zero to 10. A score below four generally is considered a patient-acceptable state, with higher scores suggesting that referral or a change in treatment should be considered.

The rheumatology evaluation then focuses on the history, physical examination, laboratory testing, and imaging directed by the clinical findings. "We don't want to expose the patient to excessive radiation," said M. Elaine Husni, MD, of the Cleveland Clinic. "If the knee is swollen and has limited range of motion, we'll focus on the knee. If the wrist is swollen and doesn't move well we'll start with imaging of the wrist and hands," she said in an interview.

"We also initially determine whether the disease is mild, moderate, or severe, which helps us with initial treatment decisions," she said. "We're lucky that we have so many treatments now. When I graduated from medical school we only had methotrexate, but now we have many choices," she said.

For the patient whose disease is mild, the treatment is likely to involve oral and topical medications, but for patients with more severe disease, options include biologics and targeted synthetic agents. The decision as to which specific medication to use depends on severity and various other factors, including symptom pattern, comorbidities, and what the patient considers the most troublesome disease manifestation, Husni noted.

Who Will Progress?

"In general, about three or four out of every 10 patients with psoriasis will develop PsA over their lifetime," said Husni. But determining which patients are most likely to progress to PsA remains uncertain. "Right now we just have clues, not a definitive paradigm," she said.

For example, patients whose skin disease affects their nails, scalp, or intertriginous areas appear to have greater risk, according to Merola. Having a first-degree relative with PsA is another strong risk factor, he explained.

In a presented at the 2021 American College of Rheumatology virtual meeting, Husni and colleagues analyzed outcomes among the Cleveland Clinic's psoriatic disease cohort, looking for clinical and demographic features that were associated with progression from psoriasis to psoriatic arthritis. Among potential predictors were age at psoriasis diagnosis, sex, family history, BMI, cardiovascular disease, nail involvement, elevated inflammatory markers, and use of tobacco and alcohol.

They found that the age at diagnosis of psoriasis was a significant predictor, with patients whose psoriasis was diagnosed at 42.6 years of age having approximately 12 fewer years before the diagnosis of PsA than those whose psoriasis was diagnosed at age 18.9 years, with a coefficient estimate of -11.88 (95% CI -13.64 to -10.12, P<0.001). "These results suggest that older patients diagnosed with psoriasis may benefit from earlier screening for PsA," said presenter, Shashank Cheemalavagu, MD, also of the Cleveland Clinic.

of patients who had moderate to severe plaque psoriasis found that patients who were treated with biologic agents were less likely to develop PsA. The authors suggested that the typical 5-to-10-year delay between the diagnosis of psoriasis and PsA could be considered a "therapeutic window of clinical opportunity for preventing the progression from psoriasis to PsA." In a multivariate analysis, the hazard ratio for the progression to PsA among patients given biologic therapy was 0.27 (95% CI 0.11-0.66, P=0.004) compared with those treated with phototherapy.

"Future large prospective and intervention studies are needed to further validate these findings in independent samples," the authors concluded.

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