Incidence of bleeding and thromboembolism and impact on overall survival in adult patients with hemophagocytic lymphohistiocytosis: A 20‐year provincial retrospective cohort study

Background Hemophagocytic lymphohistiocytosis (HLH) is a rare syndrome characterized by uncontrolled immune activation and high risk of death. There is scarce data on the incidence of bleeding and thromboembolism in HLH. Objectives To determine the cumulative incidence of bleeding and thromboembolism and impact on survival in adults with HLH. Patients/Methods We conducted a multicenter retrospective cohort study of adults with HLH in Alberta, Canada (1999-2019). The cumulative incidence of bleeding and thromboembolism were calculated, accounting for competing risks. Cox proportional hazards models were used to assess the impact of bleeding and thromboembolism on overall survival (OS). Results We identified 97 adults with HLH (median age 46 years). Venous thromboembolism (VTE) occurred in 11 (11%) patients at a median of 9 days from admission. ISTH major bleeding and clinically relevant non-major bleeding occurred in 39 (40%) patients, at a median of 16 days after admission. Nadir platelet count (adjusted odds ratio [aOR] 1.8 per log decrease, 95% confidence interval [CI] 1.2-2.8) and mechanical ventilation (aOR 4.9, 95% CI 1.8-14.8) were independent predictors of bleeding on multivariable analysis. Adjusting for competing risks, the 90-day cumulative incidences of bleeding and thromboembolism were 39% and 13%, respectively. The median OS was 18.8 months. VTE, but not bleeding, was significantly associated with adverse OS (adjusted hazard ratio 2.5, 95% CI 1.1-5.7). Conclusions In adults with HLH, VTE appears more common than previously described and is a predictor of mortality, although this may be due to unadjusted confounding. VTE prevention and treatment are challenging due to high bleeding rates.