Contributor: Gordon K. Klintworth
The disorder is a rare idiopathic multisystem disease characterterized by multiple xanthogranulomas in the viscera, bone, subcutaneous, lung, cardiovascular system, and other tissues.The lesions in the bone produce a characteristic roentgenographic appearance. Retroperitoneal fibosis is associated with cardiovascular and pulmonary lesions. Gradually, numerous cases became reported and retroperitoneal xanthogranuloma was found to be a manifestation. Although uncommon in Erdheim-Chester disease orbital involvement can occur and tends to be bilateral. The lesions are characterized by foamy macrophages with small round nuclei and abundant clear cytoplasm. The foamy macrophages result from the dissolving of lipid in the alcohol used during tissue processing (xanthoma cells). Fresh frozen tissue stains with Oil red O. Xanthelasmas  have a similar histopathologic appearance. Scattered lymphocytes and plasma cells and other inflammatory cells are also evident. Marked fibrosis and multinucleated Touton giant cells are usually present. The plasma lipid levels of affected individuals are normal suggesting that lipid metabolism is normal and that the basic defect involves the handling of lipid by macrophages.