The prevalence of psoriatic arthritis (PsA) among psoriasis patients is higher than previously thought, according to several international studies published between 2013 and 2015. In North America and Europe, between 18 and 42 percent of people with psoriasis, an inflammatory skin disease, also have psoriatic arthritis. In the United States, psoriasis affects about 2.2 percent of the population (7.5 million people), making it the most prevalent autoimmune disease in the US. In addition to skin problems associated with psoriasis, psoriatic arthritis affects the joints and other parts of the body.
Psoriatic Arthritis Prevalence Around the World
In a study published in 2013 in the Journal of the American Academy of Dermatology, researchers found 285 of the 949 study participants with psoriasis—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, whereas the highest rate—42 percent—was reported by Denmark. The prevalence rate in the United States was 36 percent. Of the 285 participants diagnosed with PsA, 117 (41 percent) didn’t know they had the disease and had never been diagnosed with it before.
“There has been a growing recognition of the higher prevalence of psoriatic arthritis in people with psoriasis,” says the lead study author Philip J. Mease, MD, director of rheumatology research at Swedish Medical Center and clinical professor of medicine at the University of Washington School of Medicine in Seattle. “People don’t have as much awareness of the disease as they optimally should. The diagnosis is out there but often misdiagnosed or under-diagnosed,” explains Dr. Mease.
A 2015 study in Brazil found a prevalence of 33% of psoriatic arthritis among people with psoriasis. A surprisingly large number of patients with PsA were not aware they had this autoimmune form of arthritis prior to entering these studies. In the study published in the Journal of Rheumatology, Brazilian researchers found 175 of the 524 psoriasis patients were diagnosed with PsA, 86 of whom were newly diagnosed. Older patients (over 50 years old) were more likely to have PsA, as well as those with nail involvement. The distribution was similar between genders, and independent of the extent of skin involvement.
In Argentina, a study published in 2014 in Clinical Rheumatology found 17 of 100 patients with psoriasis had psoriatic arthritis. In China, the prevalence of PsA in patients with psoriasis was 5.8 percent, according to a 2011 study published in the Journal of European Academy of Dermatology and Venereology. In India, 8.7 percent of 1,149 psoriasis patients were diagnosed with PsA, as reported in the Indian Journal of Dermatology, Venereology and Leprology in 2014.
The differences in the prevalence across the world illustrate that genetic and environmental effects are critical in the development of autoimmune inflammatory diseases. Another factor that contributes to disparities found between the studies is the lack of uniform disease classification criteria.
The Importance of Early Diagnosis in Psoriatic Arthritis
Because PsA is progressive and can cause irreversible joint damage, early diagnosis and treatment are critical. The earlier your condition is identified, the more likely doctors can slow or stop joint damage with medication. Treatment options may include biologics such as etanercept (Enbrel) and adalimumab (Humira), and disease-modifying antirheumatic drugs (DMARDs) such as methotrexate and the newer apremilast (Otezla).
There are several challenges in diagnosing PsA, including lack of standardized criteria and the wide range of doctors people with this condition might see. If you have symptoms of psoriatic arthritis, you may go to your primary care doctor, dermatologist or rheumatologist. “We see a lot of patients coming in with a delayed diagnosis. And now that we have such great treatments to manage the symptoms and slow down progression, we really want to find these patients,” says M. Elaine Husni, MD, vice chair of rheumatology at the Cleveland Clinic in Ohio.
How Can Psoriatic Arthritis Be Identified Earlier?
A number of educational initiatives aimed at bringing together rheumatologists and dermatologists to learn from each other about psoriasis and psoriatic arthritis have been initiated. The good news is it’s possible to diagnose the majority of PsA patients based on history and a physical exam alone, prior to the results of the lab work and X-rays. Thus dermatologists who may not order lab work or X-rays can still feel confident about identifying patients who need to be referred to rheumatologists.
As a patient, you should be proactive and tell your doctor about any joint symptoms you may be experiencing. These may include joint pain of a noticeable duration (greater than six to eight weeks), morning stiffness and joints that feel swollen or warm for days at a time.