A Curious Case of HLH: A Case Report of Hemophagocytic Lymphohistiocytosis Secondary to Atezolizumab.

A 65-year-old man presented to the hospital with multiorgan failure in the setting of recently being started on atezolizumab for his small cell lung cancer. His main clinical findings were white blood cell count of 18.9 K/μL (48% neutrophils, 32% lymphocytes, 15% monocytes, and 0% eosinophils), creatinine of 10.3 mg/dL (increased from a baseline of 1.5), transaminitis with AST of 1365 and ALT of 388, total bilirubin of 2.3, a lactic acid above 11 (the upper detectable limit of our analyzer), and a serum bicarbonate of 2.8. Imaging was only notable for splenomegaly. Upon presentation, he was intubated for airway protection and admitted to the intensive care unit. Over 3 days, he was treated for severe septic shock with multiple blood pressure medications, antibiotics, continuous renal replacement therapy (CRRT), and stress dose steroids. On Day 4, his CRRT machine began clotting with a yellow, lipidic film, leading us to consider HLH. His ferritin and triglycerides were largely elevated, and hemolysis labs showed destruction of cells, making HLH the leading diagnosis. He was started on high-dose steroids while the full interleukin panel was pending. The IL-2 soluble receptor came back elevated, confirming the diagnosis of HLH. Before this panel returned, he received one dose of tocilizumab with high-dose steroids before dying. This case is unique as it is the fourth documented case of secondary HLH due to the immune checkpoint inhibitor, atezolizumab. This presentation of HLH was also difficult due to the lack of fever, hepatomegaly, and cytopenias commonly seen as the presenting symptoms in HLH. Prompt initiation of treatment for HLH is critical, and due to this challenging presentation, this patient did not receive steroids and tocilizumab until Days 4 and 5, respectively.