Double hit lymphoma presenting as haemophagocytic lymphohistiocytosis

A 67-year-old woman with history of severe rheumatoid arthritis and use of multiple biologics including infliximab, tocilizumab and abatacept presented with fever of 39.1°C and severe pancytopenia (white blood cell count (WBC)=1.0×109/L,  absolute neutrophil count (ANC)=0.55×109/L, haemoglobin=8.7 g/dL, platelets=46×109/L). As part of the pancytopenia evaluation, imaging (CT of the chest, abdomen and pelvis) showed diffuse lymphadenopathy. Further evaluation revealed an elevated ferritin (8564 ng/mL), hypofibrinogenaemia (fibrinogen=95 mg/dL), elevated triglycerides (399 mg/dL) and a soluble interleukin 2 receptor level of 41 167 units/mL, satisfying diagnostic criteria for haemophagocytic lymphohistiocytosis (HLH). A subsequent bone marrow biopsy also revealed morphological evidence of haemophagocytosis (figure 1A), in addition to a population of very large and atypical mononuclear cells with markedly irregular, folded nuclear contours, prominent nucleoli and moderate amounts of cytoplasm (figure 1B,C). A similar large cell infiltrate was identified in …