| C Group |
|---|
| • Cutaneous non-LCH |
| - Non-XG family: includes cutaneous RDD |
| - XG family: includes JXG |
| • Cutaneous non-LCH with major systemic component |
| H Group |
| • Primary HLH (monogenic inherited conditions; FIG. 1) |
| • Secondary HLH (non-Mendelian HLH) |
| • HLH of uncertain origin |
| L Group |
| • LCH |
| • ICH |
| • ECD |
| • Mixed LCH/ECD |
| M Groupa |
| • Primary malignant histiocytoses |
| • Secondary malignant histiocytosis (following or in association with another haematological malignancy) |
| R Group |
| • Sporadic RDD |
| - Classic RDD |
| - Extranodal RDD |
| - RDD with neoplasia or immune disease |
| - Unclassified |
| • Familial RDD |
Somatic and germlme pathogenic variants associated with Histiocytic disorders are outlined in FIG. 1. ECD, Erdheim-Chester disease; HLH, haemophagocytic lymphohistiocytosis; ICH, indeterminate cell histiocytosis; JXG, juvenile xanthogranuloma; LCH, Langerhanscell histiocytosis; RDD, Rosai-Dorfman disease; XG, xanthogranuloma.
a
Malignant histiocytoses are not discussed in this review, but represent hyperproliferative, dysplastic malignancies with some histological features shared with histiocytic disorders.