Monarch Disease Ontology term MONDO_0018310 (Langerhans cell histiocytosis) (LCH) is a systemic disease associated with the proliferation and accumulation (usually in granulomas) of Langerhans cells in various tissues. Also known as: LCH, Langerhan's cell histiocytosis, Langerhans cell granulomatosis, Langerhans cell histiocytosis, NOS, Langerhans cell histiocytosis, Not otherwise specified, histiocytosis X, letterer-Siwe disease involving intra-abdominal lymph nodes, letterer-Siwe disease involving intrapelvic lymph nodes.