Case Report: Evolution of a Severe Vascular Refractory Form of ECD Requiring Liver Transplantation Correlated With the Change in the Monocyte Subset Analysis.

Erdheim-Chester disease is a rare histiocytosis characterized by iconic features associated with compatible histology. Most patients have somatic mutations in the MAP-kinase pathway gene, and the mutations occur in CD14 monocytes. Differentiation of the myeloid lineage plays a central role in the pathogenesis of histiocytosis. Monocytes are myeloid-derived white blood cells, divided into three subsets, but only the CD14CD16 "classical monocyte" can differentiate into dendritic cells and tissue macrophages. Since most mutations occur in CD14 cells and since ECD patients have a particular monocytic phenotype resembling CMML, we studied the correlation between disease activity and monocytic subset distribution during the course of a severe vascular form of ECD requiring liver transplantation. During early follow-up, increased CD14CD16 "classical monocyte" associated with decreased CD14CD16 "non-classical monocyte" correlated with disease activity. Further studies are needed to confirm the use of monocyte as a marker of disease activity in patients with ECD.