Langerhans cell histiocytosis

Langerhans cell histiocytosis is a clonal proliferation of a Langerhans cell lineage. The neoplastic cells express CD1a, S100 and langerin, and
contain Birbeck granules in the cytoplasm by electron microscopy.

The condition is also known as histiocytosis X, eosinophilic granuloma, Hand-Schüller-Christian disease, and Letterer-Siwe disease. The disease can be localized (eosinophilic granuloma), involve multiple sites (Hand-Schüller-Christian disease), or be disseminated (Letterer-Siwe disease). It also includes congenital self-healing reticulohistiocytosis of Hashimoto-Pritzker.

Morphologically, the neoplastic cells are are oval, 10 to 15 µm, and have eosinophilic cytoplasm and characteristic grooved, notched or folded nuclei with inconspicuous nucleoli. The neoplastic cells grow in sheets or clusters, depending on the site of involvement, and are usually accompanied by an admixture of eosinophils, neutrophils and lymphocytes.