Hemophagocytic lymphohistiocytosis: review of etiologies and management

George, Melissa R

Hemophagocytosis is the engulfment of hematopoietic cells by activated macrophages acting outside of usual immune system regulations. Hemophagocytic lymphohistiocytosis (HLH) covers a wide array of related diseases including HLH, autosomal recessive familial HLH (FHL), familial erythrophagocytic lymphohistiocytosis, viral-associated hemophagocytic syndrome, and autoimmune-associated macrophage activation syndrome (MAS). These disorders feature severe cytopenias due to this uncontrolled hemophagocytosis. Other laboratory signs and clinical symptoms result from disordered immune regulation and cytokine storm. The term primary HLH refers to an underlying genetic abnormality causing the disorder, whereas secondary HLH indicates that the disorder is secondary to underlying conditions such as infection, autoimmune/rheumatologic, malignant, or metabolic conditions. For the purposes of this review, FHL will indicate cases with a primary genetic cause, secondary HLH will refer to cases secondary to infection, malignancy, or metabolic disorders, and MAS will refer to cases associated with autoimmune diseases.