The diagnosis of sarcoidosis is usually made by exclusion. This disease is characterized by non-necrotizing granulomas developing most frequently in the lungs, lymph nodes, retina, hea, spleen, skin, and liver. Non-necrotizing granulomas may be seen in a number of other conditions, such as infections and ceain forms of pneumoconiosis, which must be ruled out before making a diagnosis of sarcoidosis. The etiopathogenesis of sarcoidosis is obscure. Cell-mediated mechanisms are thought to be involved in an immune response to as yet unidentified antigens. About two-thirds of patients with sarcoidosis recover without residual functional deficits, 20% have permanent pulmonary or visual damage, and 10% die of pulmonary or cardiac involvement.Also know:Asbestosis, berylliosis, and byssinosis are all lung diseases caused by inhalation of airborne dusts. Asbestosis is due to chronic inhalation of asbestos fibers, which may affect workers involved in installation and removal of insulation. Asbestosis leads to diffuse fibrosis of the lungs. In this case, granulomas are absent or scanty; the most characteristic sign of asbestos exposure is the asbestos body, which is an elongated beaded rod composed of asbestos fibers coated by proteins. Chronic exposure to beryllium in mining and fabrication leads to berylliosis , a granulomatous condition of the lungs indistinguishable morphologically from sarcoidosis. Clinical history is therefore essential in excluding this condition. Byssinosis results from occupational exposure to cotton fibers. This condition belongs to a diversified category of diseases mediated by a hypersensitivity reaction against inhaled organic dusts. Farmer's lung, pigeon breeder's lung, air-conditioner lung, and byssinosis are typical examples of these conditions, which lead to a granulomatous reaction that may progress to diffuse pulmonary fibrosis. Again, clinical history is crucial in the identification of this etiology. Ref: Wasfi Y.S., Fontenot A.P. (2003). Chapter 12. Sarcoidosis. In M.E. Hanley, C.H. Welsh (Eds), CURRENT Diagnosis & Treatment in Pulmonary Medicine.