Histological differential diagnosis of granulomatous lung diseases (Part II)

Granulomatous diseases are a heterogeneous group of the diseases of different etiology, which are manifested by a variety of clinical syndromes and variants of tissue changes, by non-uniform sensitivity to therapy and by the predominance of the common dominant histologic sign - the presence of granulomas that determine the clinical and morphological essence of each disease. Granuloma is a chronic inflammatory response, which involves macrophages and other inflammatory cells. After antigen exposure, the activation of T lymphocytes, macrophages, epithelioid cells, and multinucleated giant cells results in granuloma formation. Granuloma also contains the extracellular matrix produced by fibroblasts, which can demarcate and isolate the antigen. Granulomatous diseases are classified by their etiology as infectious and non-infectious. However, recent investigations demonstrate that pathogenic microorganisms can cause granulomas in the diseases previously considered non-infectious. In some cases, it is very difficult to classify a granulomatous process as infectious and non-infectious. The aim of this paper is to draw the attention of readers to the diversity of granulomatous diseases, to describe the key points of pathological and anatomical manifestations of various infectious diseases, and to determine an approach to the differential diagnosis of granulomatoses.