A clinical variant of Langerhans cell histiocytosis characterized by unifocal involvement of a bone (most often), skin, or lung. Patients are usually older children or adults usually presenting with a lytic bone lesion. The etiology is unknown. Morphologically, eosinophilic granuloma is characterized by the presence of Langerhans cells in a characteristic milieu which includes histiocytes, eosinophils, neutrophils, and small, mature lymphocytes.

A type of granuloma characterized morphologically by the predominance of Langerhans cells with characteristic grooved, folded, indented nuclei in the appropriate milieu that includes variable numbers of eosinophils and histiocytes including multinucleated forms, often appearing similar to osteoclasts or touton like giant cells, neutrophils and small lymphocytes. The concentration of the eosinophilic infiltrate varies from scattered mature cells to sheet-like masses of cells. Occasionally, areas of bone necrosis may interrupt the cellular infiltrate. The foamy cells may also be amassed in clumps, which are of no clinical significance because these clumps represent phagocytosis of lipid debris.

Most benign clinical form of Langerhans-cell histiocytosis, which involves localized nodular lesions of the gastric mucosa, small intestine, bones, lungs, or skin, with infiltration by eosinophils; the proliferating cell that appears to be responsible for the clinical manifestations is the Langerhans cell.

The most benign and common form of Langerhans-cell histiocytosis which involves localized nodular lesions predominantly of the bones but also of the gastric mucosa, small intestine, lungs, or skin, with infiltration by EOSINOPHILS.