Background: Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening entity which is characterized by severe hyperinflammation. Now the HLH-2004 protocol has been widely accepted and clinically used; however, many questions still remain in clinical practice. In this review, we discuss the dilemmas in the diagnosis and treatment of HLH in children.

Data sources: Original research for articles and literature reviews published in PubMed was carried out using the key term “hemophagocytic lymphohistiocytosis”.

Results: As the gene sequencing technology progresses, the range of causal mutations and primary HLH has been redefined. The monoallelic variants may contribute to the pathogenesis of the disease. Many conditions without defective cytotoxicity of T or NK cells may lead to HLH, such as primary immunodeficiency (PID) and dysregulated immune activation or proliferation (DIAP). HLH shares overlapping clinical and laboratory characteristics with severe sepsis, but usually the single values are more pronounced in HLH than sepsis. H score is another approach to help the diagnosis of secondary HLH. Specific Th1/Th2 cytokine patterns are very helpful tools to differentiate HLH (reactivation of HLH) from sepsis. Moreover, it also has been used successfully to stratify the therapy intensity. The treatment of HLH should consider underlying diseases, triggers and severity. HLH-94 is recommended for patients who need etoposide-based therapy.