**4. Middle east**

The true incidence of GCA in the Arab population is difficult to assess due to the absence of a more nationwide perspective as well as a lack of population-based study in Arab countries. In a 22-year study, the epidemiology of GCA in Saudi Arabia was investigated [14]. From 1983 to 2004, 102 patients at King Khaled Eye Specialist Hospital underwent TAB, as seen in **Figure 1**, and seven patients were identified with biopsy-proven GCA. They noted that the incidence of GCA increases with age. Regardless of this, many aspects of the healthcare system in Saudi Arabia closely resemble that of the United States, with a similar life expectancy and a ratio of ophthalmologists relative to the size of the population.

In 1980, the incidence of giant cell arteritis in Jerusalem over a 25-year period was evaluated in a study involving four general hospitals in Jerusalem [15]. Among them, 170 patients with GCA had a positive TA biopsy. Furthermore, 36 biopsynegative cases were also considered as they fulfilled the 1990 ACR criteria for GCA classification and responded adequately to steroid therapy. The age-adjusted incidence rate was computed to be 11.3 per 100,000 people ≥50 years of age for all incorporated GCA cases, but lower at 9.5 for the biopsy-proven cases. Moreover, this study observed seasonal patterns with a statistically insignificant rise in GCA diagnosis during the summer. The incidence rate of GCA in this study is comparable with those in other Mediterranean countries, with a less prominent frequency of female patients.

The results of a cohort of 114 patients who met the 2016 rACR criteria for the diagnosis of GCA and underwent TAB over a 10-year period in a tertiary center, Rassoul Akram Hospital, in Tehran, Iran were described [16]. This finding reflects the increase in GCA incidence with age. Although this study did not sufficiently provided a macroscopic account of the incidence and manifestation of GCA in a population, it was the first study performed in Iran assessing the intricacies of characterizing GCA and the discrepancies that may arise as a result of heterogeneous studies, especially due to the absence of definite criteria for the diagnosis of GCA.

#### **Figure 1.**

*A temporal artery biopsy involves acquiring a small section of the artery, which can potentially appear thrombotic. The length of the segment can vary across studies and may influence the results of the biopsy [14].* *Epidemiological Aspects of Giant Cell Arteritis DOI: http://dx.doi.org/10.5772/intechopen.105370*

## **5. Africa**

Africa stands out for its scarcity of information on GCA and its epidemiology. Perhaps, this could be due to an underdeveloped healthcare system, which hinders the proper equipment and tools for an adequate diagnosis, which could ultimately serve as data to be studied on a larger scale. It may also be that the African population has a lower susceptibility to GCA. In addition, the life expectancy in Africa is lower, which could influence statistics related to a disease with an increased likelihood of manifesting at a later stage in life. Therefore, it can be hypothesized that this region presents with lower rates of this vasculitis. The two studies discussing the epidemiology of GCA in the African population both pertain to French-colonized islands. From 1991 to 2016, data from two pathology units in Martinique, West Indies were reviewed to discuss the features of cases of biopsy-proven giant cell arteritis [17]. The findings fortified the assumption that GCA is less prevalent in an African descent population. Nevertheless, the retrospective nature of the study and the exclusion of a biopsynegative GCA may have led to an underestimation of cases of GCA.

In a retrospective study from La Reunion near the Southwest region of the Indian Ocean from 2005 to 2017, an incidence rate roughly 4–12 times lower than in most European countries was calculated [18]. An exact count was difficult to provide due to the presence of a diverse group of ethnicities in La Reunion, especially from regions of the world with a lower prevalence of GCA. A shorter life expectancy may contribute to a lower frequency of cases observed as GCA increases with age. Other characteristics were found to be analogous observations made in previous epidemiological studies.

#### **6. North America**

Studies conducted in the United States have the potential of presenting important findings due to the possibility of comparing and contrasting features of a disease between ethnicities. A retrospective study spanning 11 years was conducted in the Texas Gulf Coast. Twenty-seven out of 101,239 patients aged 40 years or older had GCA. Intriguingly, 13 of these patients were black females, rendering it a noteworthy aspect of this study in which a significantly greater proportion of patients with GCA were black individuals [19].

A report from a study spanning from 1971 to 1980 in Shelby County, Tennessee identified 26 cases of GCA [20]. The average annual incidence was computed to be 1.58 per 100,000 individuals older than 50 years of age. The predominant patient from this study was white and female. This study presents one of the lowest frequencies of GCA cases across the globe. This could partially be due to the racial makeup of this population, which has a high percentage of black residents. African descent population is assumed to present a lower incidence rate of GCA. Among other contributions to a low incidence rate such as a retrospective design as well as inconsistencies in the diagnosis criteria, this study urged the need to consider environmental factors as potential causes for the onset of the vasculitis, such as the climate, exposure to the sun, frequency of rainfall, elevation, etc.

In another region of the United States, Olmsted County, Minnesota holds a population with northern European ancestry, which appears to be the group of people most severely afflicted by GCA. Therefore, the observation of a greater incidence rate may indicate a genetic factor in the onset of GCA. Between 1950 and 1991, 125 Olmsted County inhabitants were diagnosed with giant cell arteritis. The incidence per 100,000 persons 50 years of age or older was 17.8, which was significantly higher in women than in men. The incidence of GCA had increased to 19.8 from 2000 to 2009. The annual

incidence rates substantially increased over the study period and with congregated cases of GCA, suggesting a regular cyclic pattern over time, which suggested the possibility of an infectious root for giant cell arteritis.

Previous studies suggested a low incidence of GCA in black patients, although conclusions were drawn from relatively small sample sizes. Nevertheless, the impression that GCA rarely impacts black individuals is generally assumed. Some reports have sought to compare GCA more directly between two races. A multicenter study involving 10 healthcare institutions was conducted to evaluate the presentation of GCA in African Americans [21]. An African American group of patients was compared with a cohort of Caucasian patients with a positive biopsy for ophthalmic GCA. Both the groups appeared to have a similar sex distribution, as around 70% of patients in both the cohorts were females. At Johns Hopkins Wilmer Eye Institute, findings notably challenging the commonly held belief that GCA is uncommon in African Americans were presented [22]. However, annual rates may not be directly calculated due to racial distributions in patients not reflecting that of the census population of the city of Baltimore, a detail that needs to be approached diligently prior to establishing conclusions. Furthermore, the screening and diagnosis process may differ among races and ethnicities due to physicians and clinicians holding preconceived perception of a greater prevalence in certain populations.

When comparing the rate of GCA between Caucasians and Asians, a significant lower occurrence rate of GCA in Asians was identified, which they computed to be 0.26–3.8 per 100,000 individuals older than 50 years of age, in parallel with studies from Asia [23]. The data for this study were collected from the University of California San Francisco computer database for patients from July 1989 to July 2006.

Similarly, giant cell arteritis has been reported to be very rare in Hispanics. From 1996 to 2002, patients with GCA at the Bascom Palmer Eye Institute were assessed [24]. Rates of a positive temporal artery biopsy were similar among Hispanic and non-Hispanic patients. Thirty-two patients with biopsy-proven GCA revealed similar mean age, symptoms, and final visual acuity between Hispanic and non-Hispanic cohorts. Hispanic and non-Hispanic cases are similarly impacted by the onset of giant cell arteritis.

A retrospective review was performed of all the biopsy-positive cases of giant cell arteritis presenting to a neuro-ophthalmology practice in Saskatoon, Saskatchewan [2]. Records of 141 consecutive patients who underwent temporal artery biopsy at the Saskatoon Eye Centre from July 1998 to June 2003 were reviewed. The average age of the biopsy-positive patients was 76.5 years, and the patients were 2.4 times more likely to be women. A total of 35 patients had a European ancestry, while two patients were of Aboriginal descent. The estimated incidence of GCA for Saskatoon was 9.4 per 100,000 for people over the age of 50 years. This study reveals the prospect of GCA to affect the people of Aboriginal descent despite a probable low incidence rate.

#### **7. South America**

Very few studies pertaining to the epidemiology of GCA have come from South American countries. One that most closely attempted to depict the status of GCA nationwide collected findings from three university hospitals in Brazil for patients with GCA between 2009 and 2010 [25]. This was, in fact, the first study addressing the features of GCA in Brazilian patients having the disease. Most GCA patients were Caucasians, while a few were of a combined European and Indigenous lineage. The Caucasian cohort was mostly of Portuguese, Italian, or Spanish ancestry. These suggested the possibility of asymptomatic manifestations, which may skew the epidemiological perspective of this disease.
