Hemophagocytic lymphohistiocytosis in inflammatory bowel disease: a nationwide analysis

Hemophagocytic lymphohistiocytosis (HLH) is a rare but life-threatening immune dysregulation disease. Patients with inflammatory bowel disease (IBD) can become profoundly immunocompromised due to immunosuppressive therapy, hence increasing the risk of viral infections that can trigger HLH. However, data on the association between IBD and HLH remains limited. We used data from the National Inpatient Sample (2012-2019) utilizing International Classification of Diseases (ICD)-9 or ICD-10 codes to identify individuals with IBD, either Crohn's disease (CD) or ulcerative colitis (UC), and HLH. The primary outcome was to compare the prevalence of HLH among patients with IBD with those without IBD. Secondary outcomes included in-hospital mortality, mean hospital length of stay, and description of HLH-associated triggers in IBD patients. A total of 513,322 hospitalizations included a diagnosis of IBD, 188,297 had UC and 325,025 had CD. Compared to the general population, patients with IBD were older (median age of 52 vs. 49 years, p < 0.05), more likely to be male, and of Asian/Pacific Islander descent, and had a higher median household income. There was also a higher prevalence of liver disease, autoimmune diseases, tobacco abuse, and hypothyroidism (all had p-value of < 0.001) in IBD patients. There were 94 hospitalizations identified with a diagnosis of HLH in IBD patients. Compared to patients without IBD, patients with IBD had increased odds of developing HLH (0.02% vs 0.01%, p-value < 0.001). After adjusting for various demographic characteristics, co-morbidities, and HLH-related conditions, IBD was an independent predictor for developing HLH (adjusted OR, 2.3; 95% CI, 1.847-2.866, p-value of < 0.001). There was no statistical difference between CD and UC in the odds of developing HLH. Compared to IBD patients without HLH, patients with IBD and HLH had a lower mean age at diagnosis (38 vs 52, p-value of < 0.001), higher in-hospital mortality (14.9% vs 1.5%, p-value of < 0.001), and longer mean hospital length of stay (days) (17 vs 5.4, p-value of < 0.001). Prevalence of different HLH-associated illnesses was identified in HLH patient's discharge data. Lymphoma was the most common associated malignancy (18.1%) and cytomegalovirus infection was the most common associated infection (16.0%). Our population-based study suggests that IBD is independently associated with developing HLH. Early recognition of IBD patients presenting with features suggestive of HLH is warranted to aide early diagnosis and aggressive treatment.