- Primary (genetic) HLH:
- Mendelian inherited conditions leading to HLH.
- Rare in adults.
- Associated with impaired perforin-dependent cytotoxicity of T- and natural killer (NK)-cells.
- Often triggered by an infection.
- Secondary (reactive) HLH:
- Non-Mendelian HLH.
- Accounts for nearly all of adult cases.
- May occur in setting of:
- Infection – accounts for about half of HLH cases in adults.
- Malignancy – reported in about 40%-70% of adult cases.
- Autoimmune disease – also called macrophage activating syndrome [MAS] when it occurs in this patient population.
- Transplantation
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