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The incidence of the vasculitis known as giant cell arteritis varied considerably according to geography, a meta-analysis found.

The overall global incidence of giant cell arteritis, calculated as 50-year incidence rates, was 10 per 100,000 (95% CI 9.22-10.78), reported Janet Pope, MD, of the University of Western Ontario in Canada, and colleagues.

The highest incidence was reported in Scandinavia, with 21.57 per 100,000 (95% CI 18.90-24.23), while the lowest was in East Asia, where the incidence was 0.34 per 100,000 (95% CI 0.12-0.56), as described online in.

Giant cell arteritis is a common systemic vasculitis that affects individuals older than 50, and is associated with headache, jaw claudication, tenderness of the scalp, and loss of vision. "It is thought to be caused by exaggerated immune responses to vascular endothelial injury with lymphocyte proliferation and giant cell formation," they explained. It often occurs in association with polymyalgia rheumatica. The condition can be diagnosed clinically, with imaging such as temporal artery ultrasound, or with temporal artery biopsy.

Certain autoimmune diseases such as multiple sclerosis have shown incidence-related differences according to latitude, and previous studies have suggested that giant cell arteritis is more common in northern locales such as Scandinavia and lower in Asia. There have also been reports of temporal clusters of giant cell arteritis, although this has not been confirmed.

The last comprehensive epidemiologic analysis of giant cell arteritis was published more than a decade ago. "As the population continues to age, the incidence, prevalence, and mortality of giant cell arteritis are expected to increase. Given the significant morbidity associated with giant cell arteritis from blindness, aortic defects, and treatment, a better understanding of the changing epidemiology is needed," Pope and colleagues wrote.

Therefore, they conducted a systematic review of the literature through 2019, identifying 107 studies that included at least 50 patients from multiple countries.

A total of 61 of the included studies reported on the incidence of giant cell arteritis. Areas falling between Scandinavia and East Asia in 50-year incidence rates were North and South America, at 10.89 per 100,000 (95% CI 8.78-13); Oceania, at 7.85 per 100,000 (95% CI 1.48-17.19); Europe, at 7.26 (95% CI 6.05-8.47); the Middle East, at 5.73 (95% CI 4.20-7.26); and Africa, at 4.62 (95% CI 0.05-9.20).

The relatively high rate observed in North America may be explained by the high numbers of individuals of Scandinavian ancestry residing in certain areas such as Olmsted County in Minnesota, the researchers suggested.

Denmark had the highest incidence, at 76.6 per 100,000 (95% CI 54.65-98.55), while the lowest incidence was observed in Hong Kong, at 0.34 (95% CI 0.12-0.56).

Changes in incidence also were observed over time. In Scandinavia, there was a two-thirds reduction in incidence from 1981, when the rate was 42.3 per 100,000, to 2017, when it had fallen to 13.4 per 100,000 (R²=0.58, P=0.029). This may reflect changes in immigration in Sweden, with almost one-quarter of the country's residents being foreign born in 2017.

The global pooled incidence declined yearly at a rate of 0.41 per 100,000 (R²=0.27, P=0.034).

The prevalence of giant cell arteritis was reported in nine studies, showing an overall prevalence of 51.74 per 100,000 (95% CI 42.04-61.43) through 50 years.

Mortality was reported in 37 of the included studies, with an overall rate over 50 years of 20.44 per 1,000 (95% CI 17.84-23.03). The highest mortality rate was seen in Hong Kong, at 52.63 per 1,000, and lowest in the U.S., at 34.09 per 1,000. The overall decrease in death rates per year was 0.14 per 1,000 (P=0.00076). Declining mortality may reflect greater surveillance and earlier diagnosis, as well as the increased reliance on steroid-sparing treatments, the authors suggested.

The researchers then calculated the influence of latitude, and found that only incidence correlated with latitude (R²=0.1657, β=0.489, P=0.0011). Correlations were not observed for prevalence (R²=0.1358, P=0.33) or mortality (R²=0.0002, P=0.92). The paradoxical finding that incidence and not prevalence was associated with latitude may reflect the lack of statistical power for prevalence, with only nine studies addressing this question, they explained.

The high incidence of giant cell arteritis in northern latitudes may be a result of genetic susceptibility. "Patients with giant cell arteritis have haplotype variation in certain MHC class II alleles, with a predominance of HLA DRB1*04 specifically," the researchers wrote. The Scandinavian countries also have quite advanced systems for healthcare tracking, which may detect more cases.

There also may be environmental influences, Pope told 乌鸦传媒. However, the potential role for factors such as infectious triggers remains uncertain.

A limitation of the study was its reliance on administrative data, which can reflect either overestimated or underestimated rates.

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