Erdheim Chester disease (polyostotic sclerosing histiocytosis)?
Similar to MRH, Erdheim–Chester disease is classified among the non-Langerhans cell histiocytoses. Patients usually have symptoms of bilateral, symmetric long bone pain which occurs in middle age. More than 50% of cases can have extraskeletal involvement including painless exophthalmos (can precede other manifestations), brain (pituitary and cerebellum), kidney, lung, heart (recurrent pericardial effusions), or skin involvement (xanthomas). Retroperitoneal fibrosis can occur. Radiographs of involved areas show osteosclerosis. Long bone (diaphysis > metaphysis) and facial bones are commonly affected Fig. 80.1 . Bone biopsy shows xanthogranulomatous infiltration with foamy histiocytes surrounded by fibrosis. Approximately 50% of patients have a point mutation of the BRAF gene. These patients respond to vemurafenib therapy. Corticosteroids, interferon-α, cladribine, tyrosine kinase inhibitors, and anakinra are used for therapy of patients without the gene mutation with 50% 3-year survival