The electronic database of a large health-maintenance organization was used to identify patients who had a positive temporal artery biopsy indicating a diagnosis of giant cell arteritis (GCA). The calculated incidence of GCA was significantly less than previously reported and is thought to reflect, in part, differences in population demographics between studies.
Researchers from Northern California reported findings from a regionally based study and compared the data with results of previous domestic and international studies. Walvick conducted the study in collaboration with Michael P. Walvick, DO, Kaiser Fremont Eye Clinic, Fremont, CA.
They searched the electronic medical records of Northern California enrollees in a large health-maintenence organization (Kaiser Permanente) over a contemporary 10-year period and determined that about 3,000 temporal artery biopsies had been performed, of which about 15% were positive for GCA. The annual incidence of GCA was calculated to be about five cases per 100,000 population aged 50 or more years. This rate is significantly lower than the incidence reported previously in a Mayo Clinic study, which has been considered the benchmark epidemiologic study of GCA in the United States, according to Walvick.
"There are data to suggest the incidence of GCA is lower among minorities living in North America compared with whites," Walvick said. "Based on our population size and heterogeneity, we believe our results may be better generalized to the overall U.S. population than previous studies."
Data from other studies
The higher incidence of GCA reported in the Mayo Clinic study is consistent with data from studies conducted in Scandinavian countries, according to Walwick, in a review of the literature on this topic. This agreement is not surprising considering that residents of Olmsted County, which was the focus of the Mayo Clinic study, are predominantly of Scandinavian descent, he said.
"Studies from other countries also have included predominantly white populations and were based on samples drawn from a small geographic region that was not necessarily representative of the country's population as a whole," he said.
The Kaiser Permanente study and other studies all found a predominance of women among the patients with GCA, with a female:male gender ratio in the range of about 2.5:1 to 3:1. In addition, all of the studies are in general agreement in showing diagnosis at a mean age of about 75 years.
The positive biopsy rate in the Northern California study also lies within the spectrum that has been reported by other investigators, though the reported range is fairly wide, from about 11% to 27%. Although some previous studies have found that the incidence of GCA increases with age but falls off in the oldest age group, the Northern California study showed a steady age-related rise in incidence.
Editor's Note: See "The Neuro-Connection" See more "Giant cell arteritis: An updated review."