Coexistence of intracranial Langerhans cell histiocytosis and Erdheim-Chester disease in a pediatric patient: a case report.

INTRODUCTION: The co-occurrence of Langerhans cell histiocytosis (LCH) and Erdheim-Chester disease (ECD) is extremely rare and almost all cases were reported in adults. CASE REPORT: We describe a case of intracranial LCH and ECD that was confirmed by histopathological and molecular studies. A three-year-old boy presented with headache and right exophthalmos and brain magnetic resonance images (MRI) revealed multiple intracranial tumors. Whole body MRI showed osteolytic lesions typical of LCH in flat bones and osteosclerotic changes typical of ECD in long bones. DISCUSSION: Histologically, the biopsy samples from the posterior fossa and occipital skull mass revealed areas of both LCH and ECD. Immunohistochemically, the LCH contained CD1a-positive Langerhans cells and the ECD had CD1a-negative, CD68-positive foamy histiocytes. BRAF (V600E) mutations were detected in both the LCH and ECD areas. The coexistence of LCH and ECD in the same biopsy and the BRAF (V600E) mutation status in both histologic types support the recent re-classification of the histiocytic disorder into LCH, ECD, and "mixed histiocytosis", which reflects tumorigenesis for all three from a common progenitor cell.