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Rheumatoid arthritis (RA) and psoriasis have much in common. They are both with cutaneous and joint manifestations, similar comorbidity profiles, and overlapping therapeutic options.

Mounting evidence suggesting an association between psoriasis and an increased risk of RA has underscored the need for prospective studies to enhance our understanding of the disease course and optimal treatments in patients who have both diseases, according to experts. The risks for negative consequences may be greater in patients with concomitant psoriasis and RA than with either disease alone, they cautioned.

A recent study in a nationally representation sample of the U.S. population provides new evidence highlighting the significant association between RA and psoriasis. Two times as many patients with psoriasis reported a history of RA compared with those without psoriasis (8.1% versus 4.0%), according to Amylee Martin, BS, of the University of California School of Medicine, Riverside, and colleagues in the .

"The detrimental consequences of both diseases, including physical disability, psychological distress, and risk of major adverse cardiovascular events may be higher for individuals with both diseases compared to either disease alone," the investigators wrote. "Consequently, prompt and effective treatment of both diseases is critical for patients with concomitant psoriasis and RA."

Using data from 16,066 participants in the 2009-2014 National Health and Nutrition Examination Survey (NHANES), the researchers constructed a model with RA as a dependent variable and psoriasis as an independent variable. The model was then adjusted based on gender, age, ethnicity/race, body mass index, tobacco use, and income.

Multivariate analyses revealed that the adjusted odds ratio for the association between RA and psoriasis was 1.94 (95% confidence interval [CI] 1.27-2.97, P=0.003). In subgroup analyses by age, the point estimate was higher in study participants 20 to 49 years of age compared with patients 50 years of age and older (2.82, 95% CI 1.23-6.44 versus 1.64, 95% CI 0.99-2.74). But the 95% CIs did overlap, the investigators noted.

Although the findings of the current study are limited by the self-reported nature of the data, survey items were carefully worded to minimize bias, Martin and colleagues said. The current results also support findings from their in 25,341 psoriasis patients, as well as of the Korean National Health Insurance claims database, demonstrating a 1.95 increased odds of RA in individuals with psoriasis.

"This association may be attributed to similar pathophysiology, with tumor necrosis factor-alpha (TNF-α) and interleukin-17 implicated in both disorders," Martin and colleagues wrote. "Interestingly, have been reported to paradoxically induce and/or worsen psoriasis, most commonly in individuals with RA or Crohn's disease."

In the following interview, Martin and coauthor Jashin J. Wu, MD, founder and CEO of the Dermatology Research and Education Foundation in Irvine, California, discussed the results in greater detail.

How did the strength of the association between psoriasis and RA in your current study compare with what was reported in your earlier study?

Martin: In our more recent study exploring the association between psoriasis and RA, the odds ratio was 1.9 lower compared with 3.6 in the 2012 study of the Kaiser Permanente population. However, the association was statistically significant and clinically meaningful in both studies.

Any unexpected findings?

Martin: We expected the strength of the association between psoriasis and RA to be similar in younger and older adults so we were surprised to find a stronger association in younger adults 20 to 49 years of age than in adults aged 50 and older. The impact of age on this disease association deserves further attention.

In your expert opinion, should the index of suspicion for RA be higher in patients with psoriasis?

Martin: Considering that multiple studies have demonstrated an association between the two diseases, the index of suspicion for RA should be higher in patients with psoriasis. RA should be included in the differential diagnosis when a patient with psoriasis presents with signs and symptoms of arthritis.

What is your take-home message to physicians about the clinical implications of your findings?

Wu: When a patient with psoriasis presents with joint pain, stiffness, and/or swelling, psoriatic arthritis is usually at the top of our differential diagnosis. However, RA should also be considered and psoriasis patients with suspected arthritis should be referred to a rheumatologist for further evaluation. Moreover, psoriasis and RA are both associated with an increased risk of cardiovascular disease. As such, early diagnosis and treatment of both diseases is very important for patients with concomitant disease, as it may reduce this risk.

What's next for your research?

Wu: In future studies, we plan to explore optimal treatment options for patients with concomitant psoriasis and RA. TNF-alpha inhibitors are commonly used in the treatment of RA but are associated with a small risk of worsening psoriasis symptoms. Therefore, evidence-based recommendations are needed to guide treatment selection in this specific clinical scenario.

Martin: Data are also needed to determine if the severity of each disease is intensified for patients with both psoriasis and RA.