x-type histiocytosis x-type histiocytosis x-type histiocytoses are a clinically well-defined group of cutaneous syndromes characterized by infiltrates of langerhans cells, as opposed to non-x histiocytosis in which the infiltrates contain monocytes/macrophages.: 720 conditions included in this group are:: 720–4 congenital self-healing reticulohistiocytosis langerhans cell histiocytosis x-type histiocytosisspecialtydermatology