Histiocytes are phagocytic mononuclear cells (macrophages and dendritic cells) residing in tissues. Histiocytoses are the result of pathological accumulation of macrophages or dendritic cells. Some pathologies have a very similar clinical presentation and can only be differentiated on the basis of histological image or molecular biology.

The 2024 classification published by The Histiocyte Society distinguishes:

•   Group L (Langerhans)

-         Langerhans histiocytosis

-         Erdheim-Chester disease

-         Langerhans histiocytosis associated with Erdheim-Chester disease

-         Undetermined histiocytosis

•   Group C: cutaneous or mucocutaneous non-Langerhans histiocytoses

-  Cutaneous non-Langerhansian histiocytoses

ο         Xanthogranuloma group
Juvenile xanthogranuloma
Adult xathogranuloma
Isolated reticulohistiocytoma
Benign cephalic histiocytosis
Generalized eruptive histiocytosis
Progressive nodular histiocytosis

ο         Cutaneous Rosai-Dorfman disease
Necrobiotic xanthogranuloma
Aspecific cutaneous histiocytosis

-  Systemic non-Langerhansian histiocytosis

ο         Xanthogranuloma group: disseminated xanthomas

ο         Non-xanthogranuloma group: reticulohystiocytosis

•   Group M: malignant histiocytoses

-  Primary malignant histiocytosis

-  Secondary malignant histiocytosis (associated with another hematological neoplasia)

-  Subtypes:

 Histiocytic

 Interdigitate cell

 Langerhans cell

 Undetermined cell

 Unspecified

•   Group R:

-  Familial Rosai-Dorfman disease

-  Sporadic Rosai-Dorfman disease

Classical Rosai-Dorfman disease (nodular)

Extra-nodular Rosai-Dorfman disease

Rosai-Dorfman disease associated with neoplasia

Rosai-Dorfman disease associated with an immune pathology

-  Non-C, non-L, non-M histiocytoses  

•   Group H: Hemophagocytic lymphohistiocytoses and macrophagic activation syndrome

-  Primary hemophagocytic lymphohistiocytoses (genetic origin)

-  Secondary hemophagocytic lymphohistiocytoses

-  Hemophagocytic lymphohistiocytoses of undetermined origin

Updated: July 2024