The prevalence of psoriatic arthritis (PsA) among psoriasis patients is higher than previously thought, according to a study published recently online in the Journal of the American Academy of Dermatology. The study also found a surprisingly large number of the patients with PsA were not aware they had this autoimmune form of arthritis prior to entering this study.

To better pinpoint the prevalence of PsA among psoriasis patients – estimated to be anywhere between 7 and 48 percent – an international team of researchers evaluated 949 patients at dermatology centers in seven European and North American countries who had psoriasis, an inflammatory skin disease marked by red, scaly, painful rashes. After being seen by a dermatologist, participants were sent to a rheumatologist who physically examined them, performed lab work and (where available) took X-rays.

The researchers found 285 of the 949 study participants – around 30 percent – had PsA, a disease characterized by swollen and painful joints, in addition to the scaly rashes that characterize psoriasis. When broken down by country, the lowest prevalence rate, 18 percent, was found in both Canada and Belgium, while the highest rate, 42 percent, was reported by Denmark. The prevalence rate in the United States was 36 percent. And of the 285 participants diagnosed with PsA, 117 (41 percent) didn’t know they had the disease and had never received that diagnosis before.

Lead study author Philip J. Mease, MD, director of rheumatology research at Swedish Medical Center in Seattle says in recent years there has been a growing recognition of the higher prevalence of PsA in people with psoriasis. But he says this data clearly shows more education is still needed.

“People don’t have as much awareness of the disease as they optimally should,” explains Dr. Mease, who is also a clinical professor of medicine at the University of Washington School of Medicine in Seattle. “The diagnosis is out there but often misdiagnosed or under-diagnosed.”

A delay in diagnosis of PsA can be harmful because, like other inflammatory types of arthritis, the disease is progressive and can cause irreversible joint damage. So the earlier the condition is identified, the more likely doctors will be able to slow or stop joint damage with medication, including biologics, like etanercept (Enbrel) and adalimumab (Humira), and disease-modifying antirheumatic drugs (DMARDs), like methotrexate. Several new treatments are also in the pipeline.

M. Elaine Husni, MD, vice chair of rheumatology at the Cleveland Clinic in Ohio says she welcomes the specificity of the new data and hopes it leads to better and faster diagnoses for patients. “We see a lot of patients coming in with a delayed diagnosis. And now that we have such great treatment to manage the signs and symptoms and also slow down progression, we really want to find these patients,” she says.

(A recent study found many PsA and psoriasis patients are undertreated.)

Dr. Husni agrees there are several challenges in diagnosing PsA including lack of standardized criteria and the wide range of doctors that patients with this condition might go to. “If something is wrong with your heart you go to one doctor. But with psoriatic arthritis, they could present to their primary care doctor or dermatologist or rheumatologist. Because there are so many disciplines that could be involved, it makes it more difficult as well,” she explains.

Dr. Mease notes there are currently a number of educational initiatives aimed at bringing together rheumatologists and dermatologists to learn from each other about psoriasis and PsA. And he says the silver lining out of this study is that the majority of patients who were ultimately given a PsA diagnosis got it based on history and a physical exam alone, prior to the results of the lab work and X-rays. He says that means dermatologists, who may not order lab work or X-rays as often, can still feel confident about identifying patients who need to be referred to rheumatologists – if they ask appropriate questions and correctly perform a physical (musculoskeletal) exam.

“It behooves [dermatologists] to be more cognizant of asking questions – even just a few: ‘Do you have persistent joint pain or morning stiffness or tendon pain?’ There are a few key clues that we need to embed within dermatology and other specialties,” Dr. Mease says.

Dr. Husni says patients can also be proactive by being aware of and telling their doctor about any joint symptoms they may be feeling. That includes joint pain of a noticeable duration – greater than six to eight weeks – as well as morning stiffness and joints that feel swollen or warm for days at a time.