Erdheim-Chester disease.

Erdheim-Chester disease (ECD) is a rare form of non-Langerhans' cell histiocytosis. Diagnosis of ECD is based on the identification in tissue biopsy of histiocytes, which are typically foamy and immunostain for CD68+ CD1a-. Central nervous system involvement is a major prognostic factor in ECD. Interferon alpha may be the best first-line therapy and significantly improves survival of ECD. The BRAFV600E mutation is found in more than 50% of cases. Vemurafenib has been used for a small number of patients harbouring this mutation; inhibition of BRAF activation by vemurafenib was highly beneficial in these cases of severe multisystemic and refractory ECD.