TABLE 2

Main characteristics of Langerhans cell histiocytosis (LCH), Erdheim–Chester disease (ECD) and Rosai–Dorfman disease (RDD)

	Smoking habit	Histology	Chest CT	Special techniques	Molecular abnormalities
LCH	Yes	Bronchiolocentric nodules with Langerhans cells, eosinophils and other inflammatory cells; multiple stellate-shaped nodules or fibrotic cysts separated by normal lung parenchyma	Bronchiolocentric nodules and/or fibrotic cysts with upper lobes involvement and sparing of costophrenic angles	S100⁺, CD1a⁺, Langerin⁺ factor XIIIa^- Birbeck granules at electron microscopy	BRAF (V600E) mutations in ∼30%
ECD	No	Expansion of pleura, interlobular septa and peribronchiolar tissue with xanthomatous/foamy histiocytes and interspersed inflammatory cells, multinucleate Touton-like giant cells in a fibrotic background	Thickening of pleura, interlobular septa and centrilobular nodules with/without pleural effusion and ground-glass opacities; mediastinal involvement	CD68⁺, CD163⁺, factor XIIIa⁺ CD1a^-, S100^-, Langerin^-	BRAF (V600E) mutations in ≤60%
RDD	No	Expansion of pleura, interlobular septa and peribronchiolar tissue by histiocytic cells with mixed inflammatory infiltrates and emperipolesis phenomenon	Diffuse lymphadenopathies; expansion of pleura, interlobular septa and bronchiolocentric tissue	CD68⁺, S100⁺, CD14⁺ and CD11c1 CD1a^-, Langerin^-, factor XIIIa^-	No BRAF V600E mutation

CT: computed tomography.