**1. Introduction**

The first account of giant cell arteritis (GCA) can be traced back to tenthcentury Baghdad by Arab ophthalmologist of medieval Islam Ali ibn Isa al-Kahhal. It was then more precisely described by Sir Jonathan Hutchinson in 1890, who noted the peculiar thrombotic appearance of the temporal artery (TA), a defining feature of the course of GCA. With the progression of the discovery of this disease and various case studies exploring its nature, ophthalmologists have additionally attempted to view how GCA could affect certain populations. During the second half of the twentieth century and the course of the twenty-first century, facilities across continents have published their findings on the tendencies of GCA to affect certain individuals more than others. In this chapter, we describe the epidemiology of GCA across continents and countries from individual reports and studies presenting the incidence rate of this vasculitis in their respective locations or populations.

### **2. Europe**

Europe remains the continent with the most abundant publications pertaining to the epidemiology of GCA. One of the longest studies on the epidemiology of GCA was conducted in Western Norway, a retrospective study encompassing cases from 1972 to 2012 [1]. This study was one among many that noted how changing the criteria for the identification of GCA could greatly alter its incidence, especially due to the rarity of this vasculitis. For instance, the incidence rate of patients potentially affected by GCA satisfying the ACR 1990 criteria was 16.7 per 100,000 persons over 50 years of age. The incidence of patients clinically diagnosed as having GCA was 18.4 per 100,000 persons aged 50 years or more. Meanwhile, the incidence of biopsy-proven GCA was 11.2 per 100,000 persons over 50 years of age. The extended period of this study additionally contributed to the lowering of the mean annual incidence. When solely evaluating cases during a certain 5-year period (from 1992 to 1996), the incidence rate was found to be 26.7 per 100,000 persons over 50 years of age. Regardless of this, the prevalence remained among the highest recorded globally. This study also describes the increasing GCA incidence with age, where an older individual has a greater susceptibility to acquiring this vasculitis, as well as a greater ratio of women having this disease. Similarly, in the southern region of Norway, comparisons with past records from the same set of population were provided [2]. In a study spanning a period of 14 years (2000–2013), the Hospital of Southern Norway presented a GCA occurrence rate of 16.8 per 100,000 persons over the age of 50 years, one of the highest recorded globally and in line with other epidemiological findings from the Scandinavian region. As previously noted, one must consider that a small study sample and a short study period both have the potential of overestimating the incidence of a disease, as demonstrated by this study. In the same vicinity, the rate of giant cell arteritis in Western Nyland, Finland was examined [3]. From 1984 and 1988, 54 patients were diagnosed with GCA, among which 16 patients had a positive biopsy. The retrospective annual incidence of GCA was 69.8 for every 100,000 individuals older than 50 years. From 1984 to 1990, 133 patients in Iceland fulfilling the ACR criteria for GCA were identified, rendering an incidence rate of 27 in 100,000 people older than 50 years [4]. This study also suggests that the clinicians' greater tendency to suspect GCA and perform TA biopsies (TABs) may have contributed to a higher statistical incidence. The results of these studies and their reported high mean annual incidence rates go on to highlight the possibility of a greater susceptibility to GCA among Scandinavian population. These are among the highest globally, supporting the claim that the Scandinavian population is most considerably afflicted by this inflammatory disease.

When gauging the incidence of GCA cases in other parts of Europe, we witness a lowering in the number of cases. For instance, in Italy, 285 cases of biopsy-proven GCA were observed in the Reggio Emilia area from 1986 to 2012 [5]. The adjusted incidence rate was 5.8 per 100,000 people older than 50 years of age and was significantly greater in women. In Lugo, Spain, a retrospective study was conducted from 1986 to 1995 to identify the occurrence rate of biopsy-proven GCA [6]. The mean annual incidence was computed for each 5-year period, rendering a rate of 8.26 and 10.49 per 100,000 people older than 50 years, respectively. Nearby countries and regions in the southern part of Europe presented similar incidence rates, demonstrating the moderate tendency of individuals from this area of the continent of being acquiring GCA. Namely, the incidence rate in France was concluded to be between 7 and 10 individuals out of 100,000 older than 50 years [7]. Likewise, in Slovenia, the estimated annual incidence rates of GCA were overall 8.7 per 100,000 aged greater than 50 years. This lowered rate suggests a different ethnical make

#### *Epidemiological Aspects of Giant Cell Arteritis DOI: http://dx.doi.org/10.5772/intechopen.105370*

up in the region that is perhaps less susceptible to acquiring this vasculitis, suggesting a genetic factor, while the geographical location in a lower latitude than the Scandinavian region may imply an environmental etiology. The exact etiology remains unknown.

Epidemiological studies from 2002 to 2008 in Southern Europe and Northwestern Turkey aimed to assess the epidemiology of GCA by following patients at Trakya University Medical Faculty [8]. During this period, the incidence of GCA was found to be 1.13 patients per 100,000 persons 50 years of age or older. The incidence of GCA for females was slightly greater than that for males. The fact that this study relied on a single center presents the possibility of missing individuals who sought care in a different location or simply neglected their condition. Regardless of this, the contribution of this report is crucial due to the paucity of epidemiological outlook on GCA in this space.

## **3. Asia**

A retrospective study of patients with giant cell arteritis in China was performed from August 1992 to May 2014 at the Peking Union Medical College Hospital [9]. A total of 70 patients were diagnosed with GCA. The demographic data of these patients differed from that in the previously discussed epidemiological studies in Europe. First, the average age of Chinese GCA patients was 65.2 years. This age at onset is lower than the mean reported age in other populations, which hovered between 70 and 80 years. In addition, male patients with GCA predominated the study, which differed from most reports globally. Chinese male may be more susceptible to GCA than female or they may present greater health-seeking behavior. It is important to note that patients in this study were identified from a single healthcare center, which may substantially underestimate the occurrence of this vasculitis despite its current rare occurrence. On a similar note, statistical records, pathology records, and case records from university hospitals were gathered to estimate an annual incidence of one out of 100,000 people aged older than 50 years in Hong Kong [10]. These findings suggest the particularly lower frequency of GCA among the Chinese population. In 1998, a nationwide survey was performed in Japan, revealing 690 patients treated for GCA in the previous year [11]. An incidence rate of the population was calculated to be 1.47 per 100,000 people older than 50 years of age. In conclusion, the epidemiological reports of GCA from East Asian countries reveal extremely low prevalence of GCA among this population.

From 2008 to 2014, a total of 17 patients fulfilling the classification criteria for GCA in India were identified [12]. Comparably to a previously discussed study in China, the mean age of GCA patients in the Indian population was 67 years, lower than the mean age from European reports. In addition, individuals with GCA in India were predominately male. The reasoning behind a lower mean age and a male predominant patient status is unknown and was hypothesized to be due to the greater likelihood of individuals with these characteristics to seek healthcare.

The rarity of GCA among the Indian population was demonstrated at Moorfields Eye Hospital, a center in London, UK [13]. From 2006 to 2014, patients of Indian descendance were significantly less likely to have a biopsy-positive GCA. Perhaps, some ethnicities are less likely to present a positive result to the TA biopsy or clinicians may simply be more likely to diagnose these individuals with GCA. A study of this nature, in which ethnicities are compared in a population, could provide important findings on the vulnerability of certain individuals to present with this vasculitis.
