Thoracic and paraspinal extramedullary hematopoiesis in a cat with chronic non-regenerative anemia

CASE SUMMARY: A 6-year-old neutered male domestic shorthair cat presented with non-regenerative macrocytic anemia of 2 years’ duration and minimally ambulatory paraparesis. Neurologic examination suggested an upper motor neuron paresis or T3–L3 myelopathy. The cat was positive for feline immunodeficiency virus (FIV), neutropenic, had polyclonal gammopathy and was euthanized following a hemolytic crisis. At autopsy, multifocal bilateral dark red masses were observed subpleurally around the costochondral junctions, extradurally and paraspinally in the spinal canal, and paravertebrally, on the lateral and ventral subpleural surfaces of the T4–11 vertebrae. Histologic examination of the masses revealed extramedullary hematopoietic tissue composed primarily of erythroid precursors and megakaryocytes, with occasional myeloid precursors and blood-filled sinuses. Bone marrow findings supported ineffective granulopoiesis, and decreased erythropoiesis and megakaryopoiesis, with probable myelodysplasia as the underlying cause of the hematologic abnormalities. RELEVANCE AND NOVEL INFORMATION: Thoracic, paraspinal and paravertebral extramedullary hematopoietis presenting as masses has not been described previously in cats with chronic anemia. This is a unique case of a thoracic–spinal–epidural extramedullary hematopoietic masses resulting in possible spinal cord compression and paraparesis in a cat.