Langerhans cell histiocytosis. Light micrograph of a section through a lymph node showing Langerhans cell histiocytosis (LCH), also known as granulomatosis. LCH is characterised by an increase in histiocytes, a cell of the immune system. The histiocytes move into bone, forming tumours and causing pain and swelling. Treatment is with corticosteroids, and most patients recover fully, although some will relapse. The cause of the disease is not known.