Drug-induced secondary haemophagocytic lymphohistiocytosis in hairy cell leukaemia.

Haemophagocytic lymphohistiocytosis (HLH) is a rare, aggressive, excess immune activation syndrome. Diagnosis can be challenging due to its several clinical mimics including sepsis. There are multiple aetiologies of HLH; in adults, it is most commonly triggered by infection, malignancy, drugs and autoimmune processes.