Erdheim-Chester disease: a primary macrophage cell disorder

Erdheim-Chester disease (ECD) is a rare focal or systemic infiltrative disorder resulting from xanthogranulomatous tissue deposition. Usually, bone marrow involvement affects long bone metaphyses symmetrically, but it spares the epiphyses. Retroperitoneal space, periaortic area, skin, and brain involvement have been described. Pulmonary involvement is frequent, occurring in 20% of cases. Reported histologic features in the lung include an infiltration of so-called lipid-laden macrophages and granulomatous lesions with fibrosis. Lung function outcome is unpredictable, but terminal respiratory failure is the most frequent cause of death. No effective treatment strategies have been described. We report a new case with lung and bone involvement occurring in a symptomatic woman. Histologic and electron microscopic analysis of the pulmonary infiltrate showed abnormal macrophages devoid of lipids forming nodular granulomas and rendering the previous hypothesis of this disease as a primary lipid storage disorder unlikely. These findings suggest that ECD histogenesis is instead based on a primary macrophage cell disease.