Extensive Hemophagocytic Lymphohistiocytosis Associated With Aggressive Natural Killer Cell Leukemia

An elderly woman who was previously healthy presented with fever and severe pancytopenia. Laboratory tests revealed an elevated ferritin level of 2169 μg/L, splenomegaly, and hypermetabolic lymph nodes. These clinical findings were concerning for hemophagocytic lymphohistiocytosis (HLH). A bone marrow biopsy was performed to confirm the diagnosis, but unfortunately, the identification of hemophagocytosis on the marrow aspirate was impeded by a bone marrow dry tap. However, increased histocytes and pockets of red blood cells (Figure A, arrowheads) were observed, and further CD163 immunohistochemical staining (Figure B, magnification ×400) highlighted marked hemophagocytic activity of histiocytes.