Pathogenic Idiopathic Extramedullary Hematopoiesis in a Yellow-Collared Macaw (Primolius auricollis)

1.5-year-old yellow-collared macaw (Primolius auricollis) was presented as a referral case for chronic breathing difficulties and coelomic distension. The bird was in poor body condition, and coelomic distension and green-colored urates were noted during the physical examination. Radiographic images revealed a large coelomic space-occupying soft-tissue lesion that was ultrasonographically confirmed to be hepatomegaly; the liver had a heterogeneous echogenic pattern. An ultrasound-guided fine needle aspirate of the liver was performed. The cytological results revealed immature hematopoietic cells with signs of dyserythropoiesis and were consistent with extramedullary hematopoiesis (EMH). The plasma biochemistry panel revealed a marked increase in aspartate aminotransferase and bile acids, consistent with severe hepatic disease. Following the results of the diagnostic tests, chemotherapy was initiated using hydroxyurea. Two weeks after the initial presentation and treatment, the bird died and a full postmortem examination was performed. Macroscopic examination confirmed severe hepatomegaly and severe splenomegaly. Histopathological examination of tissue samples confirmed severe EMH in the liver and spleen, splenic and renal hemosiderosis, and acute pulmonary congestion. The bone marrow was normal. The final diagnosis was pathogenic idiopathic EMH, and this case was unusual in both its presentation and severity. Extramedullary hematopoiesis is usually related to myeloid proliferative disorder, chronic blood loss, hemolytic disease, or chronic inflammatory disease. Mycobacteriosis and parasitic infection have been reported to be associated with EMH in birds; however, the inflammatory patterns seen in those cases were lacking in this case. Myeloproliferative neoplasia also appears an unlikely disease condition in this case considering that histopathology found normal architecture in the studied bone marrow; however, bone marrow abnormalities in locations other than the one sampled could not be excluded. A short review of homeostatic and pathogenic hematopoiesis in birds is provided to support the likely diagnosis of idiopathic EMH.