What is the Histiocyte Society classification of histiocytosis syndromes?

Updated: Sep 16, 2020
  • Author: Cameron K Tebbi, MD; Chief Editor: Vikramjit S Kanwar, MBBS, MBA, MRCP(UK), FAAP  more...
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Answer

The prior working classification of histiocytosis syndromes from the Histiocyte Society is as follows:

  • Dendritic-cell related

    • Langerhans cell histiocytosis

    • Xanthogranuloma

    • Erdheim-Chester disease

  • Macrophage related

    • HLH (genetic or sporadic)

    • SHML

  • Malignant disorders

    • Monocyte related, monocytic leukemia

    • Dendritic-cell related

    • Localized or macrophage related

    • Disseminated (malignant histiocytosis)

The following, adapted from the Writing Group of the Histiocyte Society, describes confidence levels for the diagnosis of class I Langerhans cell histiocytosis: [5]

  • Presumptive diagnosis - Light morphologic characteristics

  • Designated diagnosis - Light morphologic features plus 2 or more supplemental positive stains for the following:

    • Adenosinetriphosphatase

    • S-100 protein

    • Alpha-D-mannosidase

    • Peanut lectin

  • Definitive diagnosis - Light morphologic characteristics plus Birbeck granules in the lesional cell on electron microscopy and/or positive staining for CD1a antigen (T6) on the lesional cell

Prior to this system, [60] the Histiocyte Society developed a classification based on risk groups that arose from the first and second international (Langerhans cell histiocytosis I and II, respectively) trials of chemotherapy. [62] At-risk organs and systems identified in those trials included the liver, lung, spleen, and hematopoietic system. This risk classification was used in the treatment protocol of the third international study for Langerhans cell histiocytosis (LCH III). Patients were stratified into 3 groups: (1) patients with multisystem disease associated with risk organ dysfunction (2) patients with multisystem involvement but without risk organ dysfunction, and (3) those with single-system multifocal bone disease or localized involvement of special sites (intraspinal extension or involvement of the paranasal, parameningeal, periorbital, or mastoid region). In the trial, at-risk patients were randomly assigned to 1 of 2 treatment arms. Low-risk patients receive standard therapy for 6-12 months, and those with multifocal bone or special-site involvement receive the standard therapy for 6 months.


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