MULTISYSTEM NON-ARTHROPATHIC RETICULOHISTIOCYTOSIS Problems and pitfalls in the differential diagnosis of multisystem non-Langerhans cell histiocytoses

Histiocytoses are rare proliferative disorders of the mononuclear-phagocyte system. Within non-Langerhans-cell histiocytoses (NLCH), multisystem (MS) cases potentially constitute a subset at high risk of complications and progression. The current 2016 revised classification subdivides histiocytoses in 5 groups, based on highly heterogeneous criteria. Within MS-NLCH, the "L-group" includes Erdheim-Chester disease (ECD) together with Langerhans-cell histiocytosis, due to their molecular similarity; disseminated juvenile xanthogranuloma, xanthoma disseminatum and multicentric reticulohistiocytosis belong to the "C-group", because of their predominant dermatological presentation; and lastly, MS-Rosai-Dorfman disease (RDD) is listed in the specific "R-group" due to clinical and pathological findings. However, from a histopathological point of view, MS-NLCH may be divided into three categories: foamy-cell NLCH (e.g. ECD), Reticulohistiocytoses and RDD. This article is protected by copyright. All rights reserved.