Characterized by the clonal proliferation of pathogenic Langerhans cells in single or multiple organs.
Exact etiology and pathogenesis is unknown; however, it is thought to be either a malignant process or due to immune dysregulation.
Clinical presentation is heterogeneous and ranges from self-healing bone lesions to multisystem, life-threatening disease.
Tissue biopsy of lesional cells showing the presence of CD1a and langerin (CD207) is definitive for diagnosis in the correct clinical setting.
Multisystem disease is treated with systemic, multiagent chemotherapy.
Treatment of relapsed disease and central nervous system neurodegenerative disease remains a challenge.
Prognostic factors include rapid response to therapy and risk-organ involvement.
Langerhans cell histiocytosis (LCH) is a rare disease characterized by the clonal proliferation of pathogenic Langerhans cells and cytokine over-production. This leads to inflammation and tissue destruction in different organs of the body.   It may affect either a single organ system or multiple organs, and commonly involves the bone, skin, lungs, liver, spleen, bone marrow, pituitary gland, and eyes. Less common sites involved include the lymph nodes, thyroid, ears, central nervous system, gastrointestinal system, and oral mucosa.   Because pathologic Langerhans cells (dendritic cells found in the skin) are the cell type common to the various manifestations of the disease, the term "LCH" is preferred over previous names such as "histiocytosis X."   It is the most common type of histiocytosis (i.e., syndrome characterized by the abnormal proliferation of histiocytes). 
Professor of Pediatrics
University of Arkansas for Medical Sciences
Arkansas Children’s Hospital
KS declares that he serves on the Board of the Histiocytosis Association (a nonprofit organisation). He has provided advice for a legal firm reviewing a case of LCH. He receives honoraria for membership of advisory boards to Pfizer and Behring.
Professor Kimo Stine would like to gratefully acknowledge Dr Oussama Abla, a previous contributor to this topic.
Director of Pediatric Immunology, Hematology, Oncology, Bone Marrow Transplantation, and Autoimmune Diseases
Leiden University Medical Center
RME has previously worked with Dr Abla on a review of LCH. RME is an author of several references cited in this topic.
Assistant Professor of Pediatrics
Keck School of Medicine
University of Southern California
Children's Hospital Los Angeles
RJ declares that she has no competing interests.
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