Haemophagocytic Lymphohistiocytosis is being diagnosed ever more as it becomes more widely known and better understood. We ask UCLH Consultant Rheumatologist Jessica Manson to give us some insight into Primary and Secondary HLH, including the various diseases that can precipitate a Secondary case, such as rheumatology conditions, lymphoproliferative disorders and infections (including COVID-19). If you've ever found yourself confused by HLH, this is the episode for you.