Generalized lymphadenopathy secondary to isolated extramedullary hematopoiesis as an initial manifestation of primary myelofibrosis.

Extramedullary hematopoiesis (EMH) is a presence of hematopoietic activity in the extramedullary sites. EMH can occur in both benign and malignant hematologic diseases. The liver and spleen are the most common sites, but may also occur infrequently at other sites. EMH often occurs in more than one site and quite rare in an isolated organ. In this study we describe an unusual case of generalized lymphadenopathy secondary to isolated extramedullary hematopoiesis as an initial manifestation of primary myelofibrosis. Computed tomography revealed generalized lymphadenopathy including mediastinal, abdominal and pelvic lymph nodes with extensive illdefined sclerotic lesions throughout the skeletal system suggestive of lymphoma/leukemia. Lymph node biopsy showed no evidence of malignancy or granuloma, however, large abnormal cells with multilobated nuclei were seen scattered in the lymph nodes. These abnormal cells were proved to be megakaryocytes. Granulocytic precursors were less obvious on the H&E section. The diagnosis was determined as EMH in the lymph node. Bone marrow (BM) examination showed hypercellular marrow for patient's age with granulocytic and megakaryocytic proliferation with increase in BM fibrosis and reported as a myeloproliferative neoplasm, consistent with primary myelofibrosis. In summary, although EMH is not always a malignant process; it is important to stress that the patient should be investigated for underlying hematological disorders, when it is noted elsewhere.