Secondary Haemophagoyctic Lymphohistiocytosis: Diagnostic Challenges

A 60-year-old woman presented with two weeks of cough, fevers, and lethargy and tested positive for coronavirus disease 19 (COVID-19). Her past medical history was significant for extra-nodal natural killer (NK)/T-cell lymphoma, nasal type. Blood tests demonstrated multiorgan dysfunction and hyperferritinaemia. She satisfied HLH-2004 diagnostic criteria and was diagnosed with haemophagocytic lymphohistiocytosis (HLH). The HLH continued to relapse despite recovery from COVID-19 and further investigations for an underlying cause led to a diagnosis of recurrent NK/T cell lymphoma. This case illustrates the importance of recognizing the features of HLH, and of maintaining a broad differential when investigating for secondary aetiologies once the diagnosis of HLH is made.