OBSOLETE: Langerhans cell histiocytosis specific to childhood

Langerhans cell histiocytosis (LCH) specific to childhood is a term that has been classified as obsolete in the Orphanet nomenclature. It previously referred to forms of Langerhans cell histiocytosis that present during childhood. LCH is a disorder characterized by the abnormal proliferation and accumulation of Langerhans cells — a type of dendritic cell normally involved in immune surveillance — in various tissues and organs. In children, LCH can affect a wide range of body systems including the bones, skin, lungs, liver, spleen, lymph nodes, bone marrow, and the central nervous system, including the pituitary gland. Key clinical features vary depending on the organs involved and may include painful bone lesions (particularly of the skull, ribs, and long bones), skin rashes resembling seborrheic dermatitis or eczema, diabetes insipidus due to pituitary involvement, hepatosplenomegaly, lymphadenopathy, and recurrent ear infections. The disease can range from a single localized bone lesion with an excellent prognosis to a severe multisystem form that can be life-threatening, particularly in very young children with involvement of risk organs such as the liver, spleen, or bone marrow. This Orphanet entry (264724) is now obsolete and has been superseded by broader or more specific classifications of LCH. Current understanding recognizes LCH as part of a spectrum of histiocytic disorders that can occur at any age, though it is most commonly diagnosed in children aged 1 to 3 years. The pathogenesis involves activating mutations in the MAPK/ERK signaling pathway, most notably the BRAF V600E mutation, which is found in approximately 50-60% of cases. LCH is generally considered a clonal neoplastic disorder rather than a purely reactive condition. Treatment depends on the extent and severity of disease. Single-system disease, such as an isolated bone lesion, may be managed with observation, curettage, or local corticosteroid injection. Multisystem LCH typically requires systemic chemotherapy, with vinblastine and prednisone being the standard first-line regimen. Refractory or relapsed cases may be treated with salvage chemotherapy regimens, and targeted therapies such as BRAF inhibitors (e.g., vemurafenib) are increasingly being used in cases harboring the BRAF V600E mutation. Prognosis is generally favorable for single-system disease but can be guarded in multisystem disease with risk organ involvement.

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