Hemophagocytic lymphohistiocytosis in adults: A key issue in the COVID-19 era

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome characterized by persistent activation of the mononuclear phagocytic system, systemic inflammation, and hypercytokinaemia, which can lead to liver failure, “sepsis-like syndrome” and ultimately, to multiple organ failure and death. These disorders can be divided into primary and secondary (or reactive), the first, also known as familial HLH, is a genetic condition of childhood, which affects the function of TCD8 and NK cells, and usually presents in the first year of life. The secondary HLH affects mainly adults and adolescents and, it's more related to dysregulation of the immune system. In face of the COVID-19 pandemic and several reports of HLH by SARS-CoV-2, it is necessary to discuss the pathophysiology of HLH in adults more clearly. Thus, we present, for the first time, a didactic approach using illustrations and tables, compiling the most recent and relevant information to better understand this entity.