Since CAR-T cell therapy was initially approved in 2017, its use has become more prevalent and so have its side effects. CAR-T-related HLH, also named immune effector cell-associated HLH-like syndrome (IEC-HS), is a rare but fatal toxicity if not recognized promptly. We conducted a review of the literature in order to understand the prevalence of IEC-HS as well as clarify the evolution of the diagnostic criteria and treatment recommendations. IEC-HS occurrence varies between CAR-T cell products and the type of malignancy treated. Diagnosis can be challenging as there are no standardized diagnostic criteria, and its clinical features can overlap with cytokine release syndrome and active hematological disease. Suggested treatment strategies have been extrapolated from prior experience in HLH and include anakinra, corticosteroids and ruxolitinib. IEC-HS is a potentially fatal toxicity associated with CAR-T cell therapy. Early recognition with reliable diagnostic criteria and prompt implementation of treatment specific to IEC-HS is imperative for improving patient outcomes.

Hairy cell leukemia is an indolent neoplasm involving mature B cells with distinct cytologic and immunophenotypic features. It typically presents in older adults with pancytopenia and splenomegaly. We describe a patient who presented with severe anemia and thrombocytopenia, leukocytosis, and splenomegaly. He had an unusually complicated clinical course including pancytopenia refractory to multiple transfusions, oropharyngeal bleeding requiring intubation for airway protection, subdural hematoma after minor trauma, and sepsis due to Staphylococcus aureus bacteremia. This case highlights the importance of considering hairy cell leukemia in the differential diagnosis of all patients with cytopenia and splenomegaly, as this is a disease that has excellent response to treatment with purine analogs.