**9. Conclusion**

Nordic countries present the highest annual incidence rates of GCA. This vasculitis moderately affects southern European countries (Italy, Spain, France, etc.). The lowest incidence rates have been reported in East Asia. The diverse ethnical populations in countries such as United States lead to variations across regions, such as a higher incidence rate in the Northern states due to Scandinavian ancestry. Different ethnicities may present varying susceptibility because clinicians may exhibit different degree of suspicion with certain races, leading to influence on the number of biopsies performed and diagnosis made. In some regions, race and ethnicity is selfidentified, which may reveal limited information on genetic background. **Figure 2** reveals the varied incidence rate observed in different populations across the globe.

The incidence rate increases substantially with age and a greater ratio of patients are women in most regions, except for Asian countries. Whether female susceptibility is genuinely lower in that region or whether this discrepancy is due to different health-seeking behavior is unknown. Although seasonal and cyclic patterns were observed in a few studied and environmental factors were suggested, such influence remains inconclusive.

#### **Figure 2.**

*Graphical representation of incidence rates of GCA among some of the populations described in the literature. The highest incidence rates appear to be among the Scandinavian countries, regardless of the criteria utilized to diagnosis the incidence of GCA.*

The definition of giant cell arteritis is inconsistent across literature, resulting in the inclusion of heterogeneous data during extensive review. Hence, there may be an over- or underestimation of statistical values. The criteria for the diagnosis of this disease substantially varied, with incidence rates presented based on biopsyproven cases, ACR-criteria-fulfilling cases, or unspecified clinical diagnosis. Therefore, data may vary depending on which inclusion criteria were used.

Moreover, the technicality for biopsy-proven cases (length of the segment or threshold for diagnosis) may also alter the rate of incidence. In many reviews, the length of the arterial specimen remains unmentioned.

In 2016, an alteration to the list of criteria for a more comprehensive diagnosis of GCA was submitted. Furthermore, additional diagnostic tools have recently emerged, including the color Doppler ultrasound (CDUS), despite requiring extensive experience for utilization and a proper diagnosis. Other high-resolution magnetic resonance imaging technologies include magnetic resonance angiography (MRA), positron emission tomography (PET), computed tomography (CT), CT with angiography, and conventional MRA, which alternatively permit the visualization of the temporal artery. Although most reports attempted to thoroughly describe the equipment and tools for diagnosis, the heterogeneous approach across studies hinders appropriate comparisons, which may limit a precise epidemiological outlook of the disease in question.

Although this study repeatedly describes the rarity of GCA, it remains the most common vasculitis with severe consequences if remained untreated, ultimately resulting in permanent visual loss. Therefore, clinicians should remain diligent when coming across individuals presenting symptoms of the disease because an immediate course of action may greatly influence a person's course of life and impact their well-being physiologically and psychologically.
