Langerhans cell histiocytosis (LCH) is a clinically heterogeneous group of rare idiopathic disorders in which dendritic histiocytes accumulate in one or many organs. LCH is a subgroup of "L group" histiocytosis that includes Erdheim-Chester disease (ECD), indeterminate cell histiocytosis, and mixed LCH / ECD.  

LCH is a rare condition, occurring most commonly in White male children aged 1-4 years, but it may present from birth to adulthood. The 3-year survival rate is approximately 80%, with age younger than 2 years, multiorgan involvement, and organ dysfunction portending a worse prognosis.

While 4 clinical variants were previously designated (Letterer-Siwe disease, Hand-Schüller-Christian syndrome, self-healing reticulohistiocytosis of Hashimoto-Pritzker [congenital self-healing histiocytosis], and eosinophilic granuloma), these categories have been largely abandoned in recent years due to significant overlap between the clinical entities and lack of prognostic relevance. Currently, patients are classified based on the number of organ systems involved (ie, single-system or multisystem LCH).

LCH can affect any organ of the body, with bones, skin, oral mucosa, genital mucosa, nail, bone marrow, lungs, liver, spleen, gastrointestinal tract, lymph nodes, and the central nervous system being the most common sites of involvement.

LCH often presents in the first year of life as a rash in the diaper area. Other findings may include lymphadenopathy, diffuse lung involvement, osteolytic involvement of the mastoid presenting with a picture of otitis media, and gastrointestinal involvement. Failure to thrive may be due to malabsorption. There is wide variation in the clinical spectrum. The congenital form presents with papules, nodules, or ulcers at birth; nodules may be solitary or few.