[A case of Erdheim-Chester disease effectively treated by cyclophosphamide and prednisolone].

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis with a characteristic long bone lesion. Although about half of the patients have extraosseous organs, pulmonary involvement is very rare. We report a 55-year-old man with ECD who complained of severe dyspnea despite home oxygen therapy with noninvasive positive pressure ventilation. Continuous PGI2 administration was not very effective, but administration of cyclophosphamide and prednisolone induced rapid improvement of respiratory failure and the effect for six months on arterial blood gas analysis and stability of the disease state persisted.