People with psoriasis or psoriatic arthritis are far more likely to develop gout – a painful form of inflammatory arthritis – than people without these conditions, according to a large, prospective study published online recently in Annals of the Rheumatic Diseases.
Psoriasis is an inflammatory condition in which skin cells build up rapidly, causing thick, red skin overlaid with silvery patches called scales. An estimated 25 percent of people with psoriasis develop psoriatic arthritis, an inflammatory arthritis that causes painful, swollen joints in various parts of the body – especially the lower spine, fingers, toes and knees – and nail damage.
Lead study author Joseph Merola, MD, co-director of the Center for Skin and Related Musculoskeletal Diseases at Brigham and Women’s Hospital in Boston, says his group, which runs a combined dermatology and rheumatology clinic, was in a unique position to observe patients with both disorders. “We looked at our referral base, and it became apparent that many patients referred to our clinic for inflammatory arthritis actually had gout,” he explains.
Dr. Merola and his co-authors noted that psoriasis, psoriatic arthritis and gout are all linked to unusually high blood levels of uric acid, a substance that forms when the body breaks down purines, which are found in human cells and in many foods. Uric acid is thought to be a byproduct of the rapid skin cell turnover and systemic inflammation that occur in psoriasis. At least one study has shown a relationship between the severity of psoriasis and uric acid levels.
Gout occurs when excess uric acid builds up in joints and the tissue around joints – often in the big toe, but also elsewhere – and forms needle-like crystals, which can lead to sudden episodes of intense pain and swelling. If left untreated, gout can become chronic and lead to joint damage.
Because there is little research on the association between psoriasis (with and without arthritis) and the risk of gout, Dr. Merola and colleagues undertook a large-scale study of the subject. They drew participants from two large databases: the Health Professionals Follow-up Study, which collected health information on more than 51,000 male health professionals between 1986 and 2010, and the Nurses’ Health Study, which amassed similar information on nearly 122,000 female registered nurses between 1998 and 2010. All participants completed questionnaires about their medical history and lifestyle risk factors at the start of the study and at regular intervals throughout.
Participants who, in 2008, answered a question about physician-diagnosed psoriasis were included in this analysis. Of the nearly 28,000 men and 71,000 women who responded, 1,621 participants reported having psoriasis at the start of the studies, and an additional 1,334 reported developing psoriasis during the follow-up periods. Separately, 2,217 patients – 4.9 percent of men and 1.2 percent of women – developed gout during the follow-up periods.
After controlling for variables that can contribute to the development of gout – including a higher body mass index (often referred to as BMI), smoking, high blood pressure, type 2 diabetes, use of diuretics and eating certain foods – researchers found that the risk of developing gout was roughly twice as high in men and one-and-a-half times as high in women who had psoriasis than in those who did not.
Additionally, they found that for men and women with both psoriasis and psoriatic arthritis, the risk of developing gout was nearly five times greater, compared to participants with no psoriasis or psoriatic arthritis.