Tohoku J. Exp. Med., 2022 February, 256(2)

Immunohistopathological Analysis of Extramedullary Hematopoiesis and Angiogenesis of Spleen in a Case of Primary Myelofibrosis with Huge Splenomegaly

Noriaki Kawano,¹ Noriyuki Saito,² Shuro Yoshida,¹ Akira Kitanaka,³ Kotaro Shide,³ Kousuke Marutsuka,⁴ Koichi Ohshima⁵ and Kazuya Shimoda³

¹Department of Internal Medicine, Miyazaki Prefectural Miyazaki Hospital, Miyazaki, Miyazaki, Japan
²Department of Hematology, Saiseikai Fukuoka General Hospital, Fukuoka, Fukuoka, Japan
³Division of Hematology, Diabetes, and Endocrinology, Department of Internal Medicine, Faculty of Medicine, University of Miyazaki, Miyazaki, Miyazaki, Japan
⁴Department of Pathology, Miyazaki Prefectural Miyazaki Hospital, Miyazaki, Miyazaki, Japan
⁵Department of Pathology, Kurume University School of Medicine, Kurume, Fukuoka, Japan

Although splenomegaly is one of the important signs of primary myelofibrosis, the differential diagnosis varies from malignant disorders to benign disorders, including malignant lymphoma and sarcoidosis. The patient was a 67-year-old male who developed anemia and huge splenomegaly. The laboratory findings include human T-cell leukemia virus type 1 (HTLV-1) antibody, elevated soluble interleukin-2 receptor, hypocellular bone marrow, and uptake in the spleen on positron emission tomography/computed tomography scan. Additionally, we performed laparoscopic splenectomy to alleviate the clinical symptoms and to rule out malignant lymphoma. Histological findings revealed extramedullary hematopoiesis, characterized by the presence of erythroid islands and clusters of dysplastic megakaryocytes with increased reticulin fibrosis. Immunohistochemical staining revealed the presence of von Willebrand factor, dysplastic megakaryocytes, myeloperoxidase, myeloid-predominant proliferations, and CD34 immature myeloid cells. Furthermore, regarding the angiogenesis in the spleen, the endothelial cells of the capillaries and those of the sinusoidal vascular system that were reactive for CD34 and CD8, respectively, were also detected. Consequently, the histological findings revealed both extramedullary hematopoiesis and angiogenesis in spleen. Based on the histological findings and the identification of Janus activating kinase 2 (JAK-2) mutation, the patient was diagnosed with primary myelofibrosis. Splenectomy reduces blood transfusion requirements after surgery. The patient was carefully followed-up without further treatments. Thus, primary myelofibrosis is the crucial differential diagnosis of huge splenomegaly.

Keywords —— angiogenesis; extramedullary hematopoiesis; huge splenomegaly; Janus activating kinase 2 mutation; primary myelofibrosis

© 2022 Tohoku University Medical Press

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Tohoku J. Exp. Med 2022, 256, 119-125.

Correspondence: Noriaki Kawano, Department of Internal Medicine, Miyazaki Prefectural Miyazaki Hospital, 5-30 Kitatakamatsu, Miyazaki, Miyazaki 880-8510, Japan.

e-mail: kawanoriaki@yahoo.co.jp