The clinical spectrum of Erdheim-Chester disease: an observational cohort study.

Erdheim-Chester Disease (ECD) is a rare, potentially fatal, multi-organ myeloid neoplasm occurring mainly in adults. The diagnosis is established by clinical, radiologic, and histologic findings; ECD tumors contain foamy macrophages that are CD68+, CD163+, CD1a-, and frequently S100-. The purpose of this report is to describe the clinical and molecular variability of ECD. Sixty consecutive ECD patients (45 males, 15 females) were prospectively evaluated at the NIH Clinical Center between 2011 and 2015. Comprehensive imaging and laboratory studies were performed, and tissues were examined for BRAF V600E and MAPK pathway mutations. Mean age at first manifestations of ECD was 46 years; a diagnosis was established, on average, 4.2 years after initial presentation. Bone was the most common tissue affected, with osteosclerosis in 95% of patients. Other manifestations observed in one-third to two-thirds of patients include cardiac mass and periaortic involvement, diabetes insipidus, retro-orbital infiltration, retroperitoneal, lung, CNS, skin and xanthelasma, usually in combination. Methods of detection included imaging studies of various modalities. Mutation in BRAF V600E was detected in 51% of 57 biopsies. One patient had an ARAF D228V mutation, and one had an activating ALK fusion. Treatments included interferon alpha, imatinib, anakinra, cladribine, vemurafenib and dabrafenib with trametinib; eleven patients received no therapy. The diagnosis of ECD is elusive because of the rarity and varied presentations of the disorder. Identification of BRAF and other MAPK pathway mutations in biopsies improves ECD diagnosis, allows for development of targeted treatments, and demonstrates that ECD is a neoplastic disorder.