Erdheim-Chester Disease with Emperipolesis: A Unique Case Involving the Heart

Histiocytosis is an uncommon disease characterized by excessive accumulation of histiocytes.Here, we report a rare case of non-Langerhans-cell histiocytosis in a 51year-old woman who presented with severe symptoms of pericardial effusion.Radiologic investigation also detected multiple bone (lower limbs, vertebrae, ribs, and ilium) lesions.Resected pericardium showed abundant mono-or multi-nucleated non-foamy histiocytes (CD68 + /CD163 + /S-100 + /CD1  /langerin  ) in a fibroinflammatory background.The histiocytes demonstrated emperipolesis of lymphocytes, a hallmark feature of Rosai-Dorfman disease (RDD).However, molecular analysis revealed a BRAF V600E mutation of the proliferating histiocytes, highlighting the neoplastic features frequently observed in another non-Langerhans-cell histiocytosis known as Erdheim-Chester Disease (ECD).We consider this case to be a unique presentation of ECD harboring some RDD-like cells with emperipolesis, but not a case of RDD with a BRAF mutation concerning its clinical manifestation (involvement of the heart and bones) and neoplastic features.