Langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) is a rare disease of unknown cause, characterized by the proliferation of pathogenic Langerhans cells and cytokine overproduction causing inflammation, infiltration and destruction of many tissues of the body. LCH is a heterogeneous condition and may present with simple painful bony lesions, often affecting the skull or long bones, chronic otitis, proptosis or skin rash resembling seborrhoeic or napkin dermatitis. Diabetes insipidus due to hypothalamic-pituitary involvement is also well recognized. Many tissues, including lungs, CNS, liver and bone marrow may be involved in fulminant, multisystem disease (usually seen in infants, where mortality may approach 20%). Treatments may range from observation (spontaneous regression may occur), surgical curettage, steroid injection or chemotherapy. Haemopoietic stem cell transplant may be indicated in fulminant disease. International collaborative clinical trials are conducted to develop treatments of all groups. Some patients may develop chronic or relapsing disease. Survivors may have significant long-term sequelae, both from the disease or its treatment, including relapsing disease, malignancy and neurodegenerative disease of unknown origin.1,2