These activated DC recruit and activate cluster differentiation (CD) 4+ naïve T cells. Proceeding from an unknown trigger, there is abnormal maturation of vascular dendritic cells (DC) in the adventitia of the large-vessel walls. The pathological process occurring in GCA is summarised below. GCA mainly affects the medium and large arteries of the external cranial branches of the aorta. Thus, improved diagnostic pathways, specific tests and targeted management are imperative. Over the past decade there has been an increased awareness of GCA, leading to an increase in admissions for investigations for suspected GCA. In clinical practice GCA can be multifaceted: this is due to the seriousness of the condition, diagnostic uncertainty and morbidity associated with treatment. 22–83% of newly diagnosed GCA patients have imaging evidence of large-vessel GCA. The most commonly affected cranial arteries are the temporal, ophthalmic, posterior ciliary and vertebral arteries. It is a spectrum of phenotypically overlapping conditions including cranial GCA, extracranial GCA (otherwise termed large-vessel GCA, usually involving the aorta and its larger supra-aortic branches) and polymyalgia rheumatica (PMR). GCA remains a medical emergency because of the risk of sudden irreversible sight loss and stroke. It is rare in Asian and Black Caribbean/African populations. It mainly affects Caucasians and has a higher incidence in Scandinavian countries and in populations of northern European descent. Women account for 65–75% of patients the lifetime risk of GCA in women is 1% compared with 0.5% in men. The incidence of GCA increases with age, almost exclusively affecting people 50 years of age or older. It is the most common form of systemic vasculitis, with an incidence of between 15 and 25 cases per 100,000 persons over 50 years of age. Giant cell arteritis (GCA) is a granulomatous medium and large-vessel vasculitis.
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