Epidemiology

GCA typically occurs in people aged 50 years or older.[1] Its incidence rises steadily after age 50 with a mean age of onset in the eighth decade.[9][10][11] Women are affected 2 to 4 times as often as men.[9][10][12][13] The incidence of GCA in Europe in people older than age 50 is 7-29 per 100,000.[10] The incidence of GCA in southern Europe is lower than that reported from northern European populations.[14][15] An incidence rate of 32.8 per 100,000 inhabitants over the age of 50 years has been reported in Scandinavian countries, 10.2 per 100,000 in Spain, 9.2 per 100,000 in the UK, 8.7 per 100,000 in Slovenia, and 6.9 per 100,000 in northern Italy.[11][14][16][17][18] The number of incident cases of GCA will increase secondary to an ageing 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.[19] The American College of Rheumatology (ACR) classification criteria were updated in 2022 by the ACR/European Alliance of Associations for Rheumatology (EULAR).[1] These new criteria have resulted in a rise in the classification of patients diagnosed with GCA.[11]

Risk factors

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age ≥50 years

Epidemiological 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][10][12][13] It is unknown whether age-related changes in the immune system or immunosenescence is linked to this phenomenon.

female sex

Population-based studies have shown that the incidence is 2- to 4-fold higher among women than among men.[12][13] The mechanism responsible for this difference is unknown.

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genetic factors

Population-based studies have shown that the risk is higher among people of northern European ancestry, suggesting a genetic predisposition.[21] Familial aggregation has also been observed.[28] 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.[20] This genetic phenotype influences the antigen-binding site of HLA class II molecules and may therefore affect antigen selection and presentation.[20] Non-HLA genetic association has been seen with rs755374 near the IL12B region - an association that GCA shares with Takayasu's arteritis.[29] Genetic testing is not indicated as part of the diagnostic evaluation.

smoking

Case-control and cohort studies have suggested that smoking is associated with an increased risk of developing GCA.[30][31] In a meta-analysis of published observational studies, a significantly increased risk of GCA was detected among both current and ever smokers compared with non-smokers.[32]

atherosclerosis

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.[31]

environmental factors

There is circumstantial, but no conclusive, evidence that GCA may be triggered by infectious agents. Population-based studies have identified seasonal variations and cyclic fluctuations in incidence rates, suggesting the involvement of one or more environmental aetiological factors.[12][33][34]

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