Extramedullary hematopoiesis associated with myeloproliferative neoplasm manifesting as pleural effusion: Case report and review of literature

Extramedullary hematopoiesis (EMH) is a pathologic process associated with either a neoplastic myeloproliferation or a reactive hematological disorder. EMH most commonly occurs in the spleen and liver. Pleural EMH is rare and usually asymptomatic. We describe a 72-year-old man who presented with massive splenomegaly and a left pleural effusion. Pleural biopsy demonstrated EMH with an increase in CD34+ immature myeloid cells. The fluorescence in situ hybridization study performed on the myeloid cells in the pleural lesion confirmed clonal EMH with trisomy 8. The bone marrow biopsy revealed marked granulocytic and megakaryocytic hyperplasia associated with diffuse myelofibrosis. The cytogenetic study of the bone marrow showed trisomy 8. No BCR-ABL1 fusion, JAK2^V617F or MPL^W5I5K/L mutations were detected. Histological examination of the enlarged spleen showed extensive EMH associated with fibrosis. The final diagnosis of myeloproliferative neoplasm, favoring primary myelofibrosis, was given. A literature review of EMH in association with MPN is discussed.