CD1A and Langerhans cell histiocytosis: Langerhans cell histiocytosis (LCH) is a rare disease of unknown origin characterised by the proliferation of CD1a- and S-100-positive histiocytes, forming granulomas involving the reticuloendothelial system, lymph nodes, axial bones, skin, lungs, central nervous system, and particularly the pituitary gland with diabetes insipidus.