Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is an aggressive life-threatening disease that consists of uncontrolled activated lymphocytes and macrophages that secrete excessive cytokines. Symptoms and laboratory findings of HLH include prolonged fever, cytopenia, hepatosplenomegaly, liver dysfunction, hypertriglyceridemia, hyperferritinemia, increased soluble interleukin-2 receptor, low fibrinogen, and neurological problems. HLH has two forms: primary (familial autosomal recessive) or secondary (related to infections, malignancy, autoimmune and metabolic disorders, transplantations, chimeric antigen receptor T-cell therapies, etc.) form. As underlying conditions in HLH varied, clinical findings are nonspecific and disease diagnosis is challenging. Furthermore, patients diagnosed with primary HLH can have a secondary triggering agent, such as infection. Thus, there is no clear-cut distinction between these two forms. Abnormal immune response and a low number or absence of natural killer cells and cytotoxic T-lymphocytes are hallmarks of HLH. Despite the early and aggressive treatment, HLH is a deadly disease. Urgent immunosuppressive therapy is necessary to control hyperinflammation. Hematopoietic stem cell transplantation is a curative treatment in familial forms. Targeted therapy with emapalumab was also recently reported to be effective.