Hemophagocytic Lymphohistiocytosis (HLH) is a rare, life-threatening syndrome of overwhelming inflammation caused by activation and proliferation of T-lymphocytes and hemophagocytic macrophages. This uncontrolled proliferation of macrophages creates a cytokine storm with resultant tissue damage. HLH is associated with clinical and laboratory findings which include fever, cytopenias, hepatic dysfunction, splenomegaly, and marked hyperferritinemia.1-3 There exists limited epidemiologic data on adult (age ≥ 18 years) cases of HLH, and its incidence is uncertain. HLH can be due to inherited mutations causing immune system dysregulation or secondary to underlying malignancy, infection, or rheumatologic condition. Macrophage activation syndrome (MAS) refers to HLH that occurs secondary to rheumatologic diseases. Approximately 8% of HLH cases in adults occur secondary to rheumatologic diseases. The overall 30-day mortality for HLH in adult patients is approximately 44% and can be related to the underlying trigger with malignancy-associated HLH patients having a higher mortality. A key barrier to HLH treatment in adults is delay in diagnosis given the lack of specific laboratory findings to distinguish it from bacterial sepsis. The treatment for HLH in adults, beyond early initiation of steroids, remains unclear given its rarity, with much of our understanding of HLH derived from the pediatric literature.


  • The prompt diagnosis of secondary HLH in adult patients remains elusive in the absence of adult-specific diagnostic criteria. The presence of multiple HLH-2004 criteria along with the progression of laboratory data can be used to support an HLH diagnosis.
  • Not all cases of HLH in adult patients require the initiation of HLH-2004 specific therapy. HLH secondary to a rheumatologic trigger may be managed successfully with dexamethasone and IL-1 receptor blockade. Further investigation of HLH treatment in adult patients is needed.