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GCA is the most common adulthood vasculitis with an annual incidence of 1/3,000-1/25,000 adults over 50 years old. It is more frequent in populations of northern European background. GCA affects people of more than 50 years old (median age at diagnosis between 70-75 years old) and occurs twice as frequently in women as in men.

GCA often starts insidiously with general symptoms, cranial manifestations (headache, jaw claudication, scalp tenderness, visual loss), and, in about 50% of patients, polymyalgia rheumatica. Visual symptoms due to an ischemic optic neuropathy occur in 20-30% of patients, and can rapidly lead to irreversible monocular blindness. Large artery disease, including carotid or subclavian arteries, may also occur. Thoracic aortitis with aneurysms occur in approximately 15% of patients but are generally a late complication of GCA.

The etiology of giant cell arteritis is unknown. Studies have linked genetic factors, infectious agents and a prior history of cardiovascular disease to the development of giant cell arteritis.

The diagnosis of GCA can be made by a temporal artery biopsy or based on the association of demographic features (age > 50 years), clinical criteria (cranial symptoms), elevated inflammatory markers, and a favorable response to glucocorticoids. In temporal artery biopsy, the most important (and mandatory) histological criterion for the diagnosis of GCA is a mononuclear cell infiltrate predominating at the media-intima junction or involving the entire vessel wall (panarteritis). The potential role of imaging studies in the assessment of giant-cell arteritis (e.g., ultrasonography or MRI of the temporal arteries, F18 PET scan) has received increasing attention but it remains uncertain how they should best be integrated into the diagnostic workup.

In elderly patients presenting with general symptoms and elevated inflammatory markers, diagnoses of cancer or infection need to be considered. Symptoms of polymyalgia rheumatica can also point towards diagnoses of isolated polymyalgia rheumatica or rheumatoid arthritis. In some instances, biopsy-proven involvement of the temporal arteries can be seen in other systemic vasculitides, e.g., polyarteritis nodosa or microscopic polyangiitis.

Glucocorticoids are highly and rapidly effective in GCA but are often associated with substantial morbidity in an elderly population. Adjunctive immunosuppressive agents, e.g. methotrexate, have been considered to allow reduction in use of glucocorticoids. Concomitant prescription of antiplatelet or anticoagulant therapy was suggested to reduce the occurrence of ischemic events in giant cell arteritis.

The disease is chronic and the clinical course is highly variable. Approximately 50% of patients experience subsequent disease flares. Visual loss is the most feared complication.