Description

• Technically termed giant cell arteritis (GCA)
• A chronic, generalized, cellular and humoral immune-mediated vasculitis of large and medium sized vessels, predominantly affecting the cranial arteries originating from the aortic arch, although vascular involvement may be wide spread. Inflammation of the aorta is observed in 50% of cases (1).

Epidemiology

• Age of onset: >50 years
• Mean age of diagnosis: 72 years
• Most common vasculitis in individuals of Northern European descent.
• Rare in Asians and African Americans

• Prevalence in individuals >50: 1 in 500 (2)
• Highest incidence is found in Scandinavia and Northern Europe.
• Cyclic incidence: Peaking every 5–7 years
• Female predilection: 2–3:1

Risk Factors

• Increasing age >50 is the greatest risk factor
• Genetic predisposition
• Possible infective pathogens function as initial inciting agents
• Heavy smoking and atherosclerotic disease are risk factors for females, but not for males.

Genetics
The gene for HLA-DRB1–04 has been identified as a risk factor for temporal arteritis (TA), and polymorphisms of ICAM-1 have also been implicated (3).

Etiology

• The exact etiology of GCA remains unknown, although current theory suggests that advanced age, ethnicity, and specific genetic predisposition lead to a maladaptive response to endothelial injury, intimal hyperplasia, and ultimately vascular stenosis.
• TA is a chronic, systemic vasculitis primarily affecting the elastic lamina of medium- and large-sized arteries. Histopathology of affected arteries is marked by transmural inflammation of the intima, media, and adventitia, as well as patchy infiltration by lymphocytes, macrophages, and multinucleated giant cells. Mural hyperplasia can result in arterial luminal narrowing, resulting in subsequent distal ischemia.
• Current theory regarding the etiology of TA is that a maladaptive response to endothelial injury leads to an inappropriate activation of cell-mediated immunity via immature antigen-presenting cells. The subsequent release of cytokines within the arterial vessel wall can attract macrophages and multinucleated giant cells, which gives diseased vessels their characteristic histology. This also leads to an oligoclonal expansion of T-cells directed against antigens in or near the elastic lamina. Ultimately, this cascade results in vessel wall damage, intimal hyperplasia, and eventual stenotic occlusion.

Commonly Associated Conditions

Polymyalgia rheumatica (PMR) may develop either before or after the arteritis (3).