Ref:Robbins Basic Pathology (9th Edition),page no.478,479 Sarcoidosis Although sarcoidosis is considered here as an example of a restrictive lung disease, it is impoant to note that sarcoidosis is a multisystem disease of unknown etiology characterized by noncaseating granulomas in many tissues and organs. MORPHOLOGY The diagnostic histopathologic feature of sarcoidosis is the noncaseating epithelioid granuloma, irrespective of the organ involved. This is a discrete, compact collection of epithelioid cells rimmed by an outer zone of largely CD4+ T cells. The epithelioid cells are derived from macrophages and are characterized by abundant eosinophilic cytoplasm and vesicular nuclei. It is not uncommon to see intermixed multinucleate giant cells formed by fusion of macrophages. A thin layer of laminated fibroblasts is present peripheral to the granuloma; over time, these proliferate and lay down collagen that replaces the entire granuloma with a hyalinized scar. Two other microscopic features are sometimes seen in the granulomas: (1) Schaumann bodies, laminated concretions composed of calcium and proteins; and (2) asteroid bodies, stellate inclusions enclosed within giant cells. Their presence is not required for diagnosis of sarcoidosis--they also may occur in granulomas of other origins. Rarely, foci of central necrosis may be present in sarcoid granulomas, suggesting an infectious process. Caseation necrosis typical of tuberculosis is absent The lungs are involved at some stage of the disease in 90% of patients. The granulomas predominantly involve the interstitium rather than air spaces, with some tendency to localize in the connective tissue around bronchioles and pulmonary venules and in the pleura ("lymphangitic" distribution). The bronchoalveolar lavage fluid contains abundant CD4+ T cells. In 5% to 15% of patients, the granulomas eventually are replaced by diffuse interstitial fibrosis, resulting in a so-called honeycomb lung. Intrathoracic hilar and paratracheal lymph nodes are enlarged and calcification in 75% to 90% of patients, while a third present with peripheral lymphadenopathy. The nodes are characteristically painless and have a firm, rubbery texture. Unlike in tuberculosis, lymph nodes in sarcoidosis are "nonmatted" (nonadherent) and do not ulcerate.