Table 1.

Classification of histiocytoses

Histiocytosis groupDiseases
L Group LCH 
Indeterminate-cell histiocytosis (ICH) 
Erdheim-Chester Disease (ECD) 
Mixed LCH/ECD 
C Group Cutaneous non-LCH 
 Xanthomatous granuloma (XG) family: JXG, AXG, SRH, BCH, GEH, PNH 
 Non-XG family: cutaneous RDD, NXG, other 
Cutaneous non-LCH with a major systemic component 
 XG family: XD 
 Non-XG family: MRH 
R Group Familial RDD 
Sporadic RDD 
 Classical RDD 
 Extranodal RDD 
 RDD with neoplasia or immune disease 
 Unclassified 
M Group Primary Malignant Histiocytoses 
Secondary Malignant Histiocytoses 
H Group Primary HLH: Monogenic inherited conditions leading to HLH 
Secondary HLH (non-Mendelian HLH) 
HLH of unknown/uncertain origin 
Histiocytosis groupDiseases
L Group LCH 
Indeterminate-cell histiocytosis (ICH) 
Erdheim-Chester Disease (ECD) 
Mixed LCH/ECD 
C Group Cutaneous non-LCH 
 Xanthomatous granuloma (XG) family: JXG, AXG, SRH, BCH, GEH, PNH 
 Non-XG family: cutaneous RDD, NXG, other 
Cutaneous non-LCH with a major systemic component 
 XG family: XD 
 Non-XG family: MRH 
R Group Familial RDD 
Sporadic RDD 
 Classical RDD 
 Extranodal RDD 
 RDD with neoplasia or immune disease 
 Unclassified 
M Group Primary Malignant Histiocytoses 
Secondary Malignant Histiocytoses 
H Group Primary HLH: Monogenic inherited conditions leading to HLH 
Secondary HLH (non-Mendelian HLH) 
HLH of unknown/uncertain origin 

Adapted from Emile et al.21 

AXG, adult xanthogranuloma; BCH, benign cephalic histiocytosis; GEH, generalized eruptive histiocytosis; JXG, juvenile xanthogranuloma; MRH, multicentric reticulohistiocytosis; NXG, necrobiotic xanthogranuloma; PNH, progressive nodular histiocytosis; RDD, Rosai-Dorfman Disease; SRH, solitary reticulohistiocytoma; XD, xanthoma disseminatum.

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