Giant cell arteritis: Pathogenesis

Giant cell (temporal) arteritis (GCA) is an inflammatory vasculopathy that manifests in mediumsized and large arteries. The disease displays a stringent tropism for arteries with well-developed elastic membranes and essentially spares capillaries, arterioles, and veins. Not all territories in the arterial tree are equally susceptible to this vasculitis; at highest risk are the upper extremity branches of the aorta and cranial arteries. Histomorphologically, GCA is a panarteritis that is associated with the formation of multinucleated giant cells in about 50% of all cases (1). Typical histological features include the arrangement of highly activated macrophages in granulomas, focal disintegration of the muscularis, and fragmentation of the elastic lamina. There is a trend for tissue-infiltrating immune cells to form complex structures in the vicinity of the internal and external elastic laminae. Although giant cells have led to the common name of this vasculitis, the presence of these macrophage polykaryons is not essential for the diagnosis of GCA. This vasculitic process can present with diffuse mononuclear cell infiltrates without granulomatous reaction, and the blood vessel inflammation can be segmental, producing patchy lesions.