Histologic features of Giant Cell Arteritis
The “classic” pattern (only seen in ∼50% of cases) includes granulomatous inflammation of the inner half of the media, centered on the internal elastic lamina, with a mononuclear infiltrate, multinucleate giant cells, and fragmentation of the internal elastic lamina. Giant cells occur in only ∼50% of cases. In the other 50%, granulomas and giant cells are absent, and a nonspecific panarteritis is seen, including mixed inflammatory infiltrates composed largely of lymphocytes (CD4+ T cells predominate) and macrophages admixed with a few eosinophils. Neutrophils are rare. Fibrinoid necrosis should not be seen and, if present, should suggest an alternate diagnosis (e.g., granulomatous polyangiitis).
A few patients with GCA (<5%) have biopsies showing only periadventitial small-vessel vasculitis (SVV) and/or vasculitis of the vasa vasorum (VVV) surrounding a noninflamed temporal artery. These patients with SVV tend to have a lower ESR/CRP and less severe clinical manifestations and disease course than patients with isolated VVV or a classic biopsy for GCA. However, all these patients, regardless of biopsy findings, can develop blindness in up to 15% of untreated cases.
