[The differential diagnosis of Erdheim-Chester disease and IgG4-related diseases].

The paper describes Russia's first diagnosed case of Erdheim--Chester disease (systemic histiocytosis) in a 65-year-old man who has been long treated for Ormond's disease (idiopathic retroperitoneal fibrosis). It also gives the data available in the literature on the pathogenetic components of these diseases and on the similarity of many clinical, laboratory, and morphological characteristics of these two immunoinflammatory diseases and covers the issues of their differential diagnosis. Invasive procedures with a careful morphological/immunomorphological examination of biopsy specimens obtained from affected tissues are shown to be necessary for accurate diagnosis.