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. Studies in the United States have shown an increased incidence among individuals of Hispanic descent and a decreased incidence among Black children. 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. The skin is affected in approximately 33% of LCH cases. The spleen, bone marrow, and liver are considered high-risk organs. Involvement of one or more of these organs is associated with a higher risk of dying from the disease. Although the lung was previously considered a high-risk organ, it is now known to be a rare cause of death. Most patients with lung involvement have a history of tobacco smoking. Skull bone lesions are considered to be a risk factor for central nervous system involvement. These patients may have a higher risk of developing diabetes insipidus and/or neurodegenerative complications.

LCH may recur after resolution and has an unpredictable course. LCH has further been associated with the development of leukemias and lymphomas. Additionally, disease sequelae, including endocrine (diabetes insipidus, growth delay), skeletal (scoliosis, abnormal dental development, hearing dysfunction), neuropsychological (cerebellar ataxia, learning disabilities), pulmonary, and hepatic (sclerosing cholangitis, cirrhosis) involvement can present up to decades after diagnosis.

Infant Considerations:
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.

Adult Considerations:
LCH is even rarer in adults than children. The skin, bone, and lungs are most frequently involved. Systemic and progressive forms are rare.