Hemophagocytic lymphohistiocytosis in adults

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hematologic disorder characterized by unchecked immune activation and hyperinflammation, resulting in end-organ tissue damage and high mortality rates in untreated patients. Since the first description of this condition in 1939, our understanding of HLH has continued to deepen, with increasing appreciation of the differences and similarities between primary (familial) HLH and secondary (acquired) HLH. Primary HLH typically presents in the early years of life on the backdrop of inherited genetic mutations affecting cytotoxic immune cell function, whereas secondary HLH more commonly presents in adults and is a heterogeneous disorder with various potential triggers ranging from infections to malignancy, autoimmune disease, immunodeficiency, and medications. However, they converge in a common pathway of widespread systemic inflammation, which clinically manifests with fevers, organomegaly, cytopenias, laboratory derangements, and rapid development of multiorgan failure. As such, early recognition and intervention is critical to prevent irreversible organ damage and death in both primary and secondary HLH. In this review, we focus our attention on adult-onset secondary HLH and explore the latest updates on the pathophysiology, precipitants, clinical presentation, diagnosis, and management of this life-threatening condition. Primary HLH is reviewed separately as a companion article in this review series.