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

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.