Hemophagocytic lymphohistiocytosis: Pathogenesis, diagnosis, and management

Hemophagocytic lymphohistiocytosis (HLH) is a life‐threatening hyperinflammatory syndrome that is classified into primary and secondary HLH. Primary HLH consists of monogenic disorders that mainly affect the perforin‐mediated cytotoxicity of cytotoxic T lymphocytes and natural killer cells. Secondary HLH occurs as a complication in various settings such as infection, malignancy, autoimmune disease, and post‐allogeneic hematopoietic stem cell transplantation. Both primary and secondary HLH are characterized by uncontrolled hypercytokinemia that results in myelosuppression and vascular endothelium damage. More than 10% of patients with HLH die within 2 months of diagnosis due to bleeding in the visceral organs, opportunistic infection due to neutropenia, or multiple organ failure. The most obvious presentations of HLH are persistent fever refractory to antimicrobial agents and hyperferritinemia due to hypersecretion of various cytokines. The first rule is not to overlook signs of hypercytokinemia and to settle the hyperactivated immunological state as soon as possible. In addition, to improve outcome, it is essential to identify the disorders underlying HLH and provide disorder‐appropriate treatment.