Epidemiology
Giant cell arteritis (GCA) typically occurs in people ages 50 years or older.[1] The incidence of GCA rises steadily after age 50 and is highest between 70 and 80 years.[9] Women are affected 2 to 4 times as often as men.[10] Early studies suggested GCA was rare among black people but a recent retrospective cohort study found that GCA occurred at a similar rate in white and black patients, although the overall reported incidence was lower compared to other studies from the US.[11][12]
The incidence of GCA varies by geographic location. In Olmsted County, Minnesota, the average annual incidence is about 19 cases per 100,000 people ages 50 years or older.[13] This is similar to that reported in northern European populations. In contrast, the incidence of GCA in southern Europe is lower.[14] An incidence rate of 10.2 per 100,000 has been reported in Spain, 8.7 per 100,000 in Slovenia, and 6.9 per 100,000 in northern Italy.[15][16][17] An annual incidence of 12.7 per 100,000 patients ages 50 years or older was reported in Otago, New Zealand and 5.4 per 100,000 people over 50 years in South Australia.[18][19] The number of incident cases of GCA will increase secondary to an aging population; it has been estimated that between 2014 and 2050, >3 million people will have been diagnosed with GCA in Europe, North America, and Oceania.[20]
Risk factors
Epidemiologic studies have shown that there is a strong association between occurrence of GCA and advancing age. GCA almost never develops before age 50, and its incidence rises steadily thereafter.[1] The peak incidence is between 70 and 80 years; the mean age at diagnosis is 74.8 years.[9][28] It is unknown whether age-related changes in the immune system or immunosenescence is linked to this phenomenon.
Several population-based studies have shown that the incidence is 2- to 4-fold higher among women than among men.[28] The mechanism responsible for this difference is unknown, but it may relate to hormonal factors. One case-control study suggested that early menopause was associated with an increased risk (odds ratio of 3.5).[29]
Population-based studies have shown that the risk is higher among people living in northern Europe or of northern European ancestry, suggesting a genetic predisposition.[9] GCA is associated with polymorphisms of the human leukocyte antigen (HLA) class II region. The majority of patients with GCA (60%) express the B1*0401 or B1*0404/8 variant of the HLA-DR4 genotype. This genetic phenotype influences the antigen-binding site of HLA class II molecules and may therefore affect antigen selection and presentation.[21] Genetic testing is not indicated as part of the diagnostic evaluation.
Previous atheromatous disease has been associated with a 4.5-fold increase in risk in women but not in men. Evidence is based on a case-control study.[30]
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