Critical care outcomes of hemophagocytic lymphohistiocytosis in children: a single centre retrospective observational study

Background: Hemophagocytic lymphohistiocytosis (HLH) is a challenging and potentially life-threatening condition characterized by an uncontrolled inflammatory response resulting from hyperactivation of T lymphocytes and macrophages, leading to excessive production of inflammatory cytokines. HLH can lead to multiple organ failure and death in a significant proportion of cases. It is challenging to differentiate HLH from sepsis. This study aims to describe the clinical characteristics, risk factors, and outcomes of a cohort of children admitted to a pediatric intensive care unit (PICU) with primary and secondary hemophagocytic lymphohistiocytosis (pHLH and sHLH). Methods: Retrospective observational analysis of all children with HLH admitted to the PICU between 2006 and 2019. Results: Patients were evaluated at two time points: upon PICU admission (T1) and at the time of the highest ferritin level (T2). A total of 48 patients were included: 5 with pHLH, 37 with sHLH, and 6 with macrophage activation syndrome (MAS) in the context of systemic juvenile idiopathic arthritis (sJIA). The overall mortality rate in the PICU was 33.3%. Mortality rates within each group were: 60% for pHLH, 35.1% for sHLH, and nobody for MAS. The Pediatric Index of Mortality (PIM2) was higher among non-survivors. Splenomegaly and leukopenia at PICU admission were more common in non-survivors compared to survivors, as were the incidence of multiple organ failure and acute renal failure during the PICU stay. Platelet counts were significantly lower in patients who died, but only at T2. Ferritin levels remained consistently elevated in non-survivors throughout their PICU stay. Conclusions: In this cohort, mortality among children admitted to the PICU with HLH was high, particularly among those with primary or onco-hematological forms. Conversely, patients with MAS experienced more relapses but no mortality was observed in this sample. Early presence of splenomegaly, low platelet count, elevated ferritin levels, and PIM2 score at PICU admission appear to be indicators of poor prognosis. These findings may help to early identify patients at highest risk for complications and mortality.