Giant cell arteritis (GCA) is a granulomatous vasculitis of large and medium-sized arteries that occurs in individuals aged ≥50 years.1 A recent study suggested that the age at incidence of GCA may be increasing.2 To address this issue, we studied the trends in mean age at onset of GCA over a 55-year period.

A population-based incident cohort of 173 patients with GCA diagnosed between 1 January 1950 and 31 December 1999 has been established using the resources of the Rochester Epidemiology Project.^{3 4} We extended the cohort to include 34 new cases of GCA diagnosed between 1 January 2000 and 31 December 2004. Patients were included in the study if they fulfilled the 1990 American College of Rheumatology criteria.⁵ Age- and sex-specific incidence rates were calculated based on these 207 patients and adjusted to the 1980 US white population. Poisson regression models were used to estimate trends in incidence of GCA according to age, sex and calendar year of GCA diagnosis.

Table 1 shows the age- and sex-specific incidence rates for the updated cohort. There was no increase in the overall age- and sex-adjusted incidence when compared with 1995–9 (p=0.66). The mean age at incidence of GCA increased from 73.2 years for cases diagnosed between 1950 and 1979, to 76.7 years for incident cases diagnosed between 1980 and 2004 (p=0.0041; figure 1). The average age at diagnosis of GCA rose from 74.7 years in the first decade of our study (1950–9) to 79.2 years for those diagnosed in recent years (2000–4), an average increase of 4.5 years. In contrast, the average age of the Olmsted County population aged 50+ years rose from 63.1 years to 65.0 years in the same time periods, an increase of 1.9 years. There was no evidence that the increase in age over time was different in men than in women (p=0.66). Poisson regression models of trends in the age-specific incidence of GCA showed a significant interaction between age at incidence and calendar year (p=0.02). This analysis of the incidence rates showed that the increase in age at diagnosis is related to an increase in the incidence of GCA in patients >70 years, while there is no increase in the incidence of GCA in younger individuals (data not shown).

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Figure 1

Increase in the average age at incidence of giant cell arteritis between 1950 and 2004 in the population of Olmsted County, Minnesota, USA.

Over the 55-year study period, the mean age at incidence of GCA has increased by an average of 4.5 years. This observation is not entirely explained by demographic changes. A gradual but statistically non-significant increase in age at time of GCA diagnosis has been reported in a population-based study from Lugo, Spain.2 A similar increase in average age at diagnosis has been reported in rheumatoid arthritis.⁶

The increase in age at GCA diagnosis in this study appears to be related to a significant increase in the incidence of GCA in individuals aged 70+ years, while the incidence in people aged <70 years has remained relatively stable. The reasons for the observed increase in the age of onset of diagnosed GCA remain unclear. A complex interaction of environmental factors with the ageing immune system of genetically susceptible individuals may contribute to the increased incidence of GCA in those aged >70 years of age. As the longevity of the general population increases, clinicians should be vigilant for corresponding changes in the epidemiology of GCA.