What is Haemophagocytic Lymphohistiocytosis (HLH)?
HLH is a life threatening hyperinflammatory condition leading to organ dysfunction and death4. There is a loss of regulation within the immune system leading to inappropriate activation of macrophages and T-cells and a ‘cytokine storm’. This then results in an uncontrolled hyper-inflammatory state and subsequent tissue damage.1
The true prevalence of HLH is unknown in critical care; sepsis has a large overlap with HLH both in their clinical features and underlying pathophysiology, but also as sepsis can be a trigger for the condition.
It is characterised into primary or familial HLH, which usually presents in infancy, and secondary HLH which will be discussed here. The secondary form is typically triggered by an infection but may also be caused by other conditions detailed below including malignancy and autoimmune disease4. Both conditions are likely to have an underlying genetic defect; several defective cytolytic pathways have been identified in primary HLH with emerging evidence of genetic variants also seen in secondary HLH.3