The pathogenesis of giant cell arteritis: Morphological aspects

The light-microscopic, electron-microscopic and immunocytochemical characte ristics of giant cell arteritis (GCA) have been investigated in a number of studies on temporal arteries. Arterial atrophy and calcification of the in ternal elastic membrane appear to be prerequisites for the evolution of the inflammatory process. Foreign body giant cells form close to calcification s, apparently without connection with other inflammatory cells and probably by the fusion of modified vascular smooth muscle cells. The foreign body g iant cells attack the calcifications. Lymphocytes accumulate around them an d may be found in pockets in their cell surface. This focal reaction is found in atrophic, calcified arterial segments in a minority of inflamed temporal artery biopsies. More commonly seen is a dise ase mononuclear attack of the vessel wall in atrophic as well as non-atroph ic segments which lends to severe arterial dilatation. Langhans giant cells form by the fusion of macrophages in the diffuse inflammatory infiltrate. The fact that the diffusely inflamed arteries are markedly widened compared to the focally inflamed vessels suggests that the inflammatory process sta rts as a focal foreign body giant cell reaction directed at calcifications which in turn initiates a more diffuse and widespread inflammation.