Mads Okkels Birk Lorenzen, Martin Roland Jensen, Rasmus Rask Kragh Jørgensen, Paw Jensen, Henrik Frederiksen, Dennis Lund Hansen, Daniel El Fassi, Morten Nørgaard Andersen, Tarec Christoffer El‐Galaly
Adult hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening syndrome triggered by various conditions. A nationwide study of the incidence and outcomes of HLH in Denmark over 23 years (2000-2023) was performed. Adults (≥ 18 years) with HLH and triggering diseases were identified in the Danish National Patient Registry and/or the Danish Pathology Registry. A total of 325 cases were identified. The incidence increased from 0.82 per 1 million person-years (1 M-PY) (95% CI 0.61-1.04) in 2000-2011 to 4.05 per 1 M-PY (95% CI 3.56-4.53) in 2012-2023. Hematologic malignancies were the triggering diagnosis in 46% of cases, mostly lymphomas (32%). There was no clear improvement in overall survival over time. However, survival differed markedly between subgroups, with the lowest 1-year overall survival of 31% for hematologic malignancy-associated HLH, compared with 75% for idiopathic HLH. In conclusion, HLH remains a rare syndrome with a dismal prognosis, especially when associated with hematologic malignancy.