The sarcoidal granuloma: A unifying hypothesis for an enigmatic response 123

Although the cause of sarcoidosis is unknown, there is growing support for the concept that sarcoidal granulomas result from a hypersensitivity reaction producing a nonspecific response to an extrinsic or intrinsic (autoimmune) antigen in genetically susceptible individuals. The immune milieu associated with these antigens, localized in a specific cutaneous area, produces a variant of Ruocco’s “immunocompromised district.” This may explain the predilection for sarcoidal granulomas in association with foreign bodies, tattoos, herpes zoster–affected dermatomes, and scars. Similar antigenic stimulation produces sarcoidal granulomas surrounding internal tumors. Finally, systemic sarcoidosis, as manifested by hilar adenopathy, may reflect the lymphatic spread of foreign antigens.