As many as 14 percent of people with psoriasis may also have psoriatic arthritis, research shows.

Psoriatic arthritis is an autoimmune disorder that combines symptoms of psoriasis, such as dry, scaly skin, with arthritis symptoms such as joint pain and inflammation.

“People with psoriasis who complain of pain in their joints or back may have an important and treatable arthritis,” Dr. Philip S. Helliwell from University of Leeds, UK told Reuters Health.

“Most of the people we diagnosed had symptoms for many years which had been overlooked or misdiagnosed by their physicians,” he added.

The researchers estimated the prevalence of psoriatic arthritis in a sample of people coded electronically as having psoriasis by their doctor.

Overall, 633 of 22,500 patients in two general practices had a diagnostic label of psoriasis; 168 of these patients returned questionnaires and 93 were examined.

Twelve of the 93 patients (about 13 percent) were diagnosed with psoriatic arthritis, the researchers report in the journal Arthritis & Rheumatism.

On average, these 12 individuals were about 54 years old, had psoriasis for about 32 years and arthritis symptoms for about 20 years, including swollen and tender joints.

These estimates, the researchers note, are less than hospital-based estimates (which have been reported as high as 39 percent) and those based on self-report (26 percent), as well as estimates based on both community and referral populations (21 percent).

“Likely reasons for this discrepancy are the criteria for case identification and the population on whom the survey was based,” they note.

“It seems that the prevalence we found may be more if (silent) disease is taken into account,” Helliwell said, “and a number of centers are looking at asymptomatic people with psoriasis using imaging techniques such as ultrasound.”

“We are in the process of extending this study to compare three different screening tools for diagnosing psoriatic arthritis in people with psoriasis,” Helliwell added.

SOURCE: Arthritis Rheum October 15, 2009.