Non-langerhans Cell Histiocytosis- Including Erdheim-Chester Disease- and the Lung

Erdheim-Chester disease (ECD) is a rare form of non–Langerhans’ cell histiocytosis that may present with pulmonary involvement. The disease was first described as the “lipoid granulomatose” in 1930. Between then and 2013, more than 500 cases have been reported. Diagnosis of ECD is based on the identification in tissue biopsy of histiocytes, which are typically foamy and immunostain for CD68+ CD1a−. Two signs highly suggestive of ECD are 99Technetium bone scintigraphy showing nearly constant tracer uptake by the long bones and a “hairy kidney” appearance on abdominal CT scan (observed in about half such cases). As opposed to central nervous system infiltration, pulmonary involvement does not appear to be a major prognostic factor in ECD. Interferon α (and/or pegylated interferon α) may be the best first-line therapy for prolonged treatment of ECD and significantly improves survival. The BRAF V600E mutation is an activating mutation of the proto-oncogene BRAF, and is found in more than 50 % of ECD 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.