Marked granulocytic proliferation induced by granulocyte colony-stimulating factor in the spleen simulating a myeloid leukemic infiltrate

The authors describe a patient with a long-standing history of systemic lupus erythematosus and leukopenia who received multiple intermittent doses of recombinant granulocyte colony-stimulating factor (G-CSF) and who underwent splenectomy because of a clinical impression of sequestration of granulocytes by the spleen. Histologic evaluation of the spleen revealed marked granulocytic hyperplasia with an increase in immature myeloid precursors, morphologically indistinguishable from a myeloid leukemic infiltrate. A postsplenectomy bone marrow aspirate and biopsy revealed a normocellular bone marrow with active hematopoiesis and trilineage maturation. The bone marrow aspirate cultured cells showed no numeric or structural chromosomal abnormality. Extramedullary hematopoiesis after receipt of G-CSF was previously reported, but, to our knowledge, ours is the first report of morphologic changes virtually identical to a leukemic infiltrate in spleen after G-CSF treatment. We describe the histologic and immunohistochemical findings in the spleen, compare our observations with those of others reported in the literature, and postulate a possible mechanism for this phenomenon.