Erdheim-Chester disease: evidence for a disease entity different from Langerhans cell histiocytosis? Three cases with detailed radiological and immunohistochemical analysis.

Erdheim-Chester (EC) disease is a rare pathological entity with a highly specific and characteristic pattern of radiographic bone changes. Histologically it resembles Langerhans cell histiocytosis (LCH), and it is still a matter of discussion whether EC disease is a distinct entity or a type of LCH. In this study, 3 cases of Erdheim-Chester disease were followed up over years and examined in detail both radiologically and immunohistochemically. All 3 cases showed the pathognomonic skeletal features for EC disease as well as an identical immunohistochemical phenotype quite different from LCH. Macrophages and Touton cells reacted strongly positive with the histiocytic marker CD 68, whereas staining with S100 and CD1a, markers for Langerhans cells, were negative. Both the immunohistochemical phenotype and the bone changes were clearly distinct from LCH.