People with psoriasis appear to have an increased risk for lymphoma, according to an article in the November issue of the Archives of Dermatology. The skin disease, which can be painful and disfiguring in severe cases, affects roughly 1 to 2 percent of the population.

Previous research had suggested that people with psoriasis may be at an increased risk for developing lymphoma. In the current study, an international team investigated whether the rate of lymphoma in patients with a history of psoriasis is different from the rate of lymphoma in matched patients without psoriasis.

The researchers studied a random sample of 10 percent of patients 65 years or older (2,718 patients with psoriasis; 105,203 without it) who were registered with a general practitioner who contributed to the British General Practice Research Database between 1988 and 1996. Median follow-up for all patients was 46 months.

During the study period, the authors identified 276 diagnosed cases of lymphoma (type unspecified). "Patients with psoriasis had an almost 3-fold increased rate of lymphoma compared with patients without psoriasis," the authors wrote. "Patients 65 years or older who had psoriasis developed an additional 122 lymphomas per 100,000 patients annually."

After reviewing the medical records of patients with psoriasis who had lymphoma, the researchers found that "all patients with psoriasis who developed systemic lymphoma were treated with medications consistent with psoriasis and had outcomes consistent with the diagnosis of lymphoma (namely, referral to an oncology service)."

"Additional studies are necessary to determine if the increased rate of lymphoma is related to psoriasis severity, psoriasis treatment, or an interaction between these risk factors," the authors concluded.