Hemophagocytic Lymphohistiocytosis (HLH)

Key notes

  • HLH is a rare but potentially fatal hyperinflammatory and immune-dysregulation syndrome.

  • It involves excessive activation of:

    • T lymphocytes.
    • Macrophages.
    • Other immune cells.

  • It may be:

    • Primary/familial, due to genetic defects.
    • Secondary/acquired, triggered by infections, malignancies, autoimmune diseases or immune disorders.
  • Common triggers include viral infections, especially Epstein–Barr virus, cancers and rheumatological conditions.

  • Important clinical features:

    • Persistent fever.
    • Enlarged spleen.
    • Cytopenias.
    • Liver dysfunction.
    • Neurological symptoms.

  • Laboratory findings may include:

    • Very high ferritin.
    • High triglycerides.
    • Low fibrinogen.
    • Raised soluble IL-2 receptor.
    • Evidence of hemophagocytosis.
  • HLH can resemble severe sepsis.
  • Treatment aims to suppress uncontrolled immune activation and address the underlying trigger.
  • It is relevant to internal medicine, immunology and public health.