Table 2.

Proposed Revised Classification of Histiocytocytic Disorders

L Group	LCH Intermediate-cell histiocytosis (ICH) Erdheim-Chester disease (ECD) Mixed LCH/ECD
C Group	Cutaneous non-LCH -Xanthomatous granuloma (XG) family: includes JXG -Non-XG family: includes cutaneous RDD Cutaneous non-LCH with major systemic component -XG family: xanthoma disseminatum -Non-XG: multicentric reticulohistiocytosis
R Group	Familial RDD Sporadic RDD -Classic RDD -Extranodal RDD -RDD with neoplasia or immune disease -Unclassified
M Group	Primary malignant histiocytosis Secondary malignant histiocytosis
H Group	Primary HLH Secondary HLH (non-Mendelian) HLH of unknown/uncertain origin

LCH, Langerhans cell histiocytosis; ECD, Erdheim-Chester disease; JXG, juvenile xanthogranuloma; RDD, Rosai-Dorfman disease; HLH, hemophagocytic lymphohistiocytosis. Adapted from²