What is sarcoidosis?

The Seventh International Conference on Sarcoidosis gave the following definition:
“Sarcoidosis is a multisystem granulomatous disorder of unknown etiology. It most commonly affects young adults and presents most frequently with bilateral hilar lymphadenopathy, pulmonary infiltration, and skin or eye lesions. The course and prognosis may correlate with the mode of onset. An acute onset with erythema nodosum heralds a self-limiting course and spontaneous resolution, whereas an insidious onset may be followed by relentless, progressive fibrosis.”