When the immune system turns against itself in a hyperinflammatory storm
In short: Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening syndrome driven not by infection, but by an immune system that cannot stop activating. This uncontrolled state can mimic sepsis, yet its management requires a fundamentally different approach to prevent total systemic collapse.
At its core, HLH is a hyperinflammatory state characterized by the disproportionate activation of the immune system. Unlike typical autoimmunity, which targets specific self-antigens, HLH is driven by a lack of regulation. Animal models suggest the mechanism involves overactive CD8+ T cells, which trigger the overactivation of macrophages via interferon-gamma. This process creates a dangerous cycle of inflammation that poses an imminent threat to life, often requiring diagnosis and treatment in acute care settings.
The origins of the syndrome differ significantly by age. Pediatric patients typically present with the primary, or heritable, form of HLH, which is defined by specific immune deficiencies. In contrast, adolescent and adult patients generally develop the acquired form. This secondary version can be triggered by infections—notably EBV—autoimmune diseases, or malignancies. Notably, malignancies, particularly lymphomas, are associated with the poorest prognosis and account for up to 70% of adult cases.
Recent advancements in immunotherapy, such as CAR-T cell therapy, have also been linked to cytokine release syndrome, a condition that can manifest as HLH. Because of the high mortality rate and the potential for confusion with sepsis, early initiation of immunosuppressive treatment is critical. While the disease is difficult to track due to suspected underdiagnosis, retrospective data from the United States National Inpatient Sample showed 330 adult cases diagnosed during hospitalization in a single year, with a mean age of 50.1 years.
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Sources
- Summary by Intellect · source: HLH I Hemophagocytic Lymphohistiocytosis - cause, pathophysiology, investigation and treatment
- Also: Hemophagocytic Lymphohistiocytosis for the Internist and Other Primary Care Providers
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