Presse Med
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In a compatible clinico-radiological setting, the diagnosis of Erdheim-Chester disease (ECD) involves the analysis of histiocytes in tissue biopsies: they are typically foamy and CD68+ CD1a, whereas in Langerhans cell histiocytosis (LCH) they are CD68+ CD1a+. Overlap forms of histiocytoses are frequent. Technetium bone scintigraphy showing nearly constant tracer uptake by the long bones is highly suggestive of ECD and a 'hairy kidney' appearance on abdominal CT scan is observed in more than half ECD cases. ⋯ More than 50 cases harboring BRAF mutation and with severe multisystemic and refractory ECD (sometimes associated with LCH) have been treated worldwide with vemurafenib, a BRAF inhibitor that proved to be very beneficial. Other recurrent mutations of the MAPK (NRAS, MAP2K1) and PIK3 pathways (PIK3CA) have been found among ECD patients. As recurrent mutations in the MAPK pathway are found in ECD and LCH on a background of chronic inflammation, we believe that both conditions should be redefined as an inflammatory myeloid neoplasia.