• Clinical and laboratory picture is similar to primary (genetic) HLH. Distinction between the two may be difficult.

• Affects more older patients, often immunocompromised.

• Commonly associated with underlying viral/bacterial infection when called infection-associated haemophagocytic syndrome (IAHS).

• Triggered by a wide variety of infections including (especially) EBV and malaria. Also associated with some malignancies (usually involving T cells) and lipid infusions.

Treatment and outcome: Good survival rates if underlying infection easily treatable. Otherwise has high mortality.

Class III: Malignant histiocytosis

Monocyte-derived acute leukaemias account for 10% of AMLs arising in children. What used to be called 'malignant histiocytosis' with hepatosplenomegaly, fever, wasting and pancytopenia and tissue infiltration with large monocytoid cells is now recognised as a lymphocyte-derived lymphoma (large cell anaplastic, CD30+, ffl p198). It is doubtful whether true histiocyte-derived malignancies other than AML occur in children.

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