Central nervous system juvenile xanthogranuloma with malignant transformation.

Juvenile xanthogranuloma (JXG) is a rare histiocytic disorder that typically manifests in the skin. Here, we describe a patient with JXG diffusely involving the central nervous system (CNS), whose disease responded to therapy but subsequently underwent dissemination to the peritoneum and bone marrow. Repeat biopsy at dissemination revealed pleomorphic histiocytes with tetraploidy, suggesting evolution to a clonal histiocytic neoplasm. Despite further chemotherapy, the patient died of disease progression. This case highlights the clinical and pathological heterogeneity of JXG and the difficulty of treating multi-focal CNS disease.