Histiocytosis
Basics
DESCRIPTION
- Histiocytic disorders are derived from mononuclear phagocytic cells and dendritic cells. They are divided into three groups.
- Dendritic cell disorders (e.g., Langerhans cell histiocytosis [LCH], juvenile xanthogranuloma [JXG], Erdheim-Chester disease)
- Macrophage-related disorders (e.g., hemophagocytic lymphohistiocytosis [HLH], macrophage activation syndrome [MAS], Rosai-Dorfman disease)
- Malignant histiocytosis (lymphoma subtype)
- LCH (the focus of this chapter) results from the clonal proliferation of immature myeloid dendritic cells that share similar morphologic expression to skin LCH cells.
- Other names include the following (Langerhans cell histiocytosis is the preferred terminology):
- Histiocytosis X, Hand-Schüller-Christian syndrome, Letterer-Siwe disease, eosinophilic granuloma
- Hashimoto-Pritzker syndrome: infant dermatologic involvement, often self-limited
EPIDEMIOLOGY
- 2 to 10 cases per million children
- LCH may occur at any age. Median age is 30 months.
- Single-system disease in 55% of patients; multisystem disease is more common in children 1 to 3 years of age.
- Male-to-female ratio approximately 1
- May be more common in whites of northern European descent than African Americans
RISK-FACTORS
GENETICS
- No evidence that relatives of LCH patients are at increased risk of disease.
- Very rare reports of recurrence within families
- Specific HLA alleles associated with disease phenotype in some case series
PATHOPHYSIOLOGY
- Single-system LCH: limited to one organ system; most commonly bone, followed by skin
- Multisystem LCH involves two or more organs/systems with or without risk organs.
- Risk organs include hematopoietic system, liver, and/or spleen and portend a worse prognosis. Lungs are no longer considered a risk organ.
- CNS risk lesions: Lesions in the facial or anterior or middle cranial fossa bones are associated with 3 times increased risk of CNS involvement.
- CNS lesions can include mass lesions, pituitary stalk involvement, or neurodegenerative disease.
ETIOLOGY
LCH etiology is incompletely understood. BRAFV600E mutations are found in ~60% of cases but are not prognostic. Activation of the RAS/MAPK/MEK/ERK pathway is common regardless of BRAF mutation status. Inflammatory infiltrates and abnormal cytokine production in lesions are common, although role in disease remains unclear.
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Citation
Cabana, Michael D., editor. "Histiocytosis." Select 5-Minute Pediatrics Topics, 7th ed., Wolters Kluwer Health, 2015. Medicine Central, im.unboundmedicine.com/medicine/view/Select-5-Minute-Pediatric-Consult/14094/all/Histiocytosis.
Histiocytosis. In: Cabana MDM, ed. Select 5-Minute Pediatrics Topics. Wolters Kluwer Health; 2015. https://im.unboundmedicine.com/medicine/view/Select-5-Minute-Pediatric-Consult/14094/all/Histiocytosis. Accessed September 7, 2024.
Histiocytosis. (2015). In Cabana, M. D. (Ed.), Select 5-Minute Pediatrics Topics (7th ed.). Wolters Kluwer Health. https://im.unboundmedicine.com/medicine/view/Select-5-Minute-Pediatric-Consult/14094/all/Histiocytosis
Histiocytosis [Internet]. In: Cabana MDM, editors. Select 5-Minute Pediatrics Topics. Wolters Kluwer Health; 2015. [cited 2024 September 07]. Available from: https://im.unboundmedicine.com/medicine/view/Select-5-Minute-Pediatric-Consult/14094/all/Histiocytosis.
* Article titles in AMA citation format should be in sentence-case
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