People who undergo treatment for severe psoriasis are five times more likely to develop brain tumors than the general population, researchers reported last week.
Psoriasis, a chronic skin disorder characterized by red, scaly patches, affects as many as 4 million Americans. The cause of the disease is unknown.
An 11-year study, sponsored by the National Institute of Arthritis and Musculoskeletal and Skin Diseases, tracked about 1,300 people who have been treated for severe psoriasis, defined as psoriasis affecting more than 30% of the body.
All the subjects had undergone at least one session of a combination of drug and ultraviolet light therapy, called PUVA, and most had also used topical tar shampoos and lotions to treat their discomfort, said Dr. Robert Stern, the dermatologist who headed the study.
The study found the incidence of brain tumor five times greater among people with severe psoriasis than among people their age without severe psoriasis.
Researchers do not know what causes the higher rate of brain tumors among people with severe psoriasis. No higher risk was found among people with mild or moderate psoriasis, who usually do not undergo PUVA therapy.
"This has been puzzling us for some time. We don't believe it is related to PUVA therapy," said Stern, of Beth Israel Hospital in Boston.