Pathology of sarcoidosis

The role of pathology in the diagnosis of sarcoidosis is identification of granulomas in tissue specimens and performance of studies to exclude known causes of granulomatous inflammation. The granulomas of sarcoidosis are nonspecific lesions that, by themselves and in the absence of an identifiable etiologic agent, are not diagnostic of sarcoidosis or any other specific disease. Among the diseases to be excluded are mycobacterial, fungal, and parasitic infections, chronic beryllium disease and other pneumoconiosis, hypersensitivity pneumonitis, and Wegener's granulomatosis. Even after extensive workup a substantial number of granulomas will remain unclassified. Not every disease that features nonnecrotizing granulomas of undetermined etiology is sarcoidosis. The granulomas of sarcoidosis may exhibit focal necrosis of minimal amount. In cases with granulomas that exhibit a greater degree of necrosis an infectious or other nonsarcoid etiology should be strongly suspected. Strict clinical, radiological, and pathological criteria must be used for diagnosis. In cases that exhibit necrotizing granulomas with more than minimal, focal necrosis, extrathoracic involvement only, and/or incompatible clinical and radiological findings, the diagnosis of sarcoidosis should be approached with great caution. The diagnosis is most secure when compatible clinical and radiological findings are supported by the demonstration of microorganism-negative, nonnecrotizing granulomas in a biopsy specimen accompanied by biopsy evidence or strong clinical evidence of multisystem involvement, and negative cultures for bacteria, mycobacteria, and fungi. A positive Kveim-Siltzbach test provides strong support for the diagnosis of sarcoidosis.