Background Hemophagocytic lymphohistiocytosis (HLH) is a rare syndrome of excessive immune activation associated with high mortality. Early diagnosis and treatment can reduce mortality among these patients.

Objectives To determine the rate of mortality independently and according to the cause in patients with HLH.

Methods Pubmed database with the MeSH terms (“lymphohistiocytosis, hemophagocytic” [MeSH Terms] OR (“lymphohistiocytosis” [All Fields] AND “hemophagocytic” [All Fields]) OR “hemophagocytic lymphohistiocytosis” [All Fields] OR (“hemophagocytic” [All Fields] AND “lymphohistiocytosis” [All Fields])) AND cases [All Fields] were queried which yielded 466 results. Case series referenced from these studies were also studied. 74 studies were identified out of which the studies with a sample size smaller than 10 were excluded. 48 studies were kept with a total of 1983 patients. Meta analysis was performed to combine the mortality rates of all studies and studies of patients with the same cause. The results were presented in a Forest plot. Prior to the meta analysis, the heterogeneity test on mortalities was conducted to choose a fixed or random effects model. I², a common heterogeneity measure, was reported with 25%, 50%, 75% suggesting low, moderate, and high heterogeneity.

Results The combined mortality rate for all studies was 41.99% [95% confidence interval (CI) 36%>49%]. In studies of patients with EBV infection (n=4), the combined mortality rate was 44% (95% CI 18%>74%) whereas the mortality rate in studies with other infections (n=4) was 46% (95% CI 13–83%). The mortality rate in patients with hematological malignancy (n=8) was higher at 60% (95% CI 44%>74%]. For studies of patients with autoimmune diseases (n=2) and in transplant (n=4) patients, the combined mortality rate was 11% (95% CI 5%>21%) in patients with autoimmune disease and 38% (95% CI 27%>51%) in transplant patients. I² for the mortalities of all studies and each cause was presented as follows: I²=0% (p=0.764) for autoimmune disease, I²=94.8% [89.6%; 97.4%] (p<0.0001) for EBV infection, I²=75.2% [50%; 87.7%] (p=0.0002) for hematological malignancy, I²=75.2% [50%; 87.7%] (p=0.0002) for infection malignancy, I²=89.2% [75.1%; 95.3%] (p<0.0001) for other infection, and I²=0% [0%; 52.1%] (p=0.811) for transplant. The heterogeneity test result remained significant but for the causes of autoimmune disease and transplant.

Conclusions Based on our results, mortality is higher in patients with hematological malignancy compared to patients with other causes, whereas it is lower in patients with autoimmune disease.

Disclosure of Interest None declared