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10 slides generated from the cancer page, with a quiz from the open benchmark and speaker notes that cite the sources. Arrow keys move between slides; Print gives one slide per page.
Single-system Langerhans cell histiocytosis is the milder form of this rare histiocytosis, in which the abnormal immune cells affect only one organ, usually a bone or the skin, in a child or young adult. Single bone lesions often heal after biopsy or curettage, skin disease may fade by itself, and gentle vinblastine and prednisone is kept for multiple bone lesions or lesions near the brain.
Langerhans cell histiocytosis is a clonal myeloid neoplasm of CD1a- and langerin-positive dendritic-like cells, driven in most cases by BRAF V600E or another MAPK pathway mutation. Its behaviour depends on how many organs are involved. Single-system disease, most often a lytic bone lesion of the skull, femur, ribs or vertebrae in a child of school age, or a skin eruption in an infant, carries almost no mortality; the classic eponyms eosinophilic granuloma (bone), Hand-Schüller-Christian and Letterer-Siwe disease have given way to a classification by organ count and risk-organ involvement. Pulmonary Langerhans cell histiocytosis in adults who smoke is a distinct single-system form that often improves with smoking cessation. The Histiocyte Society staging separates unifocal bone disease, multifocal bone disease, special-site lesions (skull base, orbit, mastoid and vertebrae with soft tissue extension, which carry a risk of later pituitary or neurodegenerative involvement) and single-system disease of skin, lymph node or lung.
Treatment is proportionate. A single bone lesion is treated by biopsy with curettage, sometimes with an intralesional steroid injection, and many heal spontaneously; indomethacin or bisphosphonates help painful bone disease; skin-only disease in infants is observed or treated topically and often resolves, though a proportion of infants later develop multisystem disease and must be followed. Multifocal bone disease and special-site lesions are treated with the same vinblastine and prednisone regimen used for multisystem disease, given for twelve months after LCH-III showed longer treatment reduced reactivation, in order to prevent recurrence and the late central nervous system complications. Reactivation is common but rarely dangerous. Adults with single-system disease may receive cytarabine or cladribine instead because vinblastine is more toxic in adults, and BRAF or MEK inhibitors are reserved for refractory disease. The main long-term concerns are diabetes insipidus and neurodegenerative disease after skull-base lesions, and orthopaedic sequelae after vertebral collapse, so follow-up continues for years.
| Setting | Approach | Guideline |
|---|---|---|
| Diagnosis and staging | Biopsy with immunohistochemistry and BRAF testing; skeletal survey or whole-body imaging, blood count, liver tests and abdominal ultrasound to exclude multisystem disease. | not mapped |
| Unifocal bone disease | Biopsy with curettage, with or without intralesional methylprednisolone; observation of healing; indomethacin for pain. | not mapped |
| Multifocal bone or special-site disease | Vinblastine and prednisone for twelve months (LCH-III schedule) to reduce reactivation and central nervous system risk. | not mapped |
| Skin-only disease | Observation or topical corticosteroids; systemic therapy only for extensive symptomatic disease; regular review for progression to multisystem disease. | not mapped |
| Adult single-system or refractory disease | Cytarabine or cladribine; smoking cessation for pulmonary disease; BRAF or MEK inhibitors (vemurafenib, dabrafenib-trametinib, cobimetinib) for refractory disease. | not mapped |