Sarcoidosis is a chronic granulomatous disease of unknown etiology, frequently involving the respiratory tract. Its incidence is approximately between 6 and 10 per 100 000, with a slight female predominance and a peak age at onset of between 20 and 40 years. Sarcoidosis has the greatest incidence in Sweden. In the United States, it more commonly affects African Americans.
Histologically, sarcoidosis is characterized by multiple epithelioid and giant cell granulomas. The granulomas are formed by tight aggregates of epithelioid histiocytes; they are characteristically noncaseating and are surrounded by a sparse mixed inflammatory infiltrate. Giant cells, typically of Langerhans type, are usually present and may contain intracytoplasmic inclusions, including star-shaped structures called asteroid bodies and calcific laminated structures called Schaumann bodies. Special stains for infectious organisms are negative in sarcoid granulomas.