Pulmonary sarcoidosis: a mimic of respiratory infection

Sarcoidosis is an idiopathic multisystem disorder with several clinical and roentgenographic features suggestive of respiratory infection. In the absence of infection, it is characterized by the microscopic presence of noncaseating epithelioid granuloma in affected tissues. When present, constitutional symptoms, fever, coughing, and exertional dyspnea usually develop insidiously, although occasionally Lofgren's syndrome--the triad of bilateral hilar adenopathy, erythema nodosum and polyarticular arthritis--may herald the onset of acute disease. Pulmonary involvement is the roentgenographic hallmark of sarcoidosis; bilateral hilar adenopathy is the most common manifestation. However, parenchymal infiltrates and pleural effusion may occur. Although numerous bacterial and fungal organisms may mimic the clinical and roentgenographic features of sarcoidosis, tuberculosis and fungal infections associated with granulomatous inflammation are the infectious processes most apt to cause diagnostic confusion. Several diagnostic clues are available to the clinician confronted with the consideration of sarcoidosis. Roentgenographic staging of the disorder (stage 0, normal radiograph; stage I, isolated bilateral hilar adenopathy; stage II, hilar adenopathy and parenchymal involvement; stage III, isolated parenchymal involvement; and stage IV, parenchymal fibrosis) provides a framework on which a differential diagnosis of likely infectious agents may be constructed and a history of travel to regions of endemic fungal infection may further narrow the differential diagnosis. An unexplained exudative lymphocytic pleural effusion or CD-4 lymphocyte predominance in bronchoalveolar lavage (BAL) fluid may also suggest a diagnosis of sarcoidosis. However, the definitive diagnosis of sarcoidosis is dependent upon the histological demonstration of noncaseating granuloma and the exclusion of infection in the appropriate clinical and roentgenographic setting.