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

Abstract

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.

Keywords: Chronic anemia; NHS-EMH; non-hepatosplenic extramedullary hematopoiesis; spinal cord compression; thoracic–spinal–epidural EMH.

Figure 1

Blood film from the cat on day 508. (a) Many ‘ghost’ erythrocytes (arrowhead) are present. Structures suggestive of Mycoplasma haemofelis are seen on an erythrocyte (arrow) and on a ghost cell (arrowhead) (Wright’s stain). (b) The nucleated cells consist of a lymphocyte on the left, and two nucleated erythrocytes (rubricyte) on the right. The nucleated erythrocyte on the far right appears dysplastic, with abundant cytoplasm (Wright’s stain). (c) Marked agglutination. The increased background density is likely due to hyperproteinemia and hemoglobinemia (Wright’s stain). (d) A giant dysplastic platelet (arrow) (Wright’s stain)

Figure 2

(a) The thoracic cavity contains multiple, dark-red, bilateral, subpleural paracostal masses (extramedullary hematopoietic [EMH] tissue) at the level of ribs 2–12 (arrows), as well as paraspinal/paravertebral EMH tissue (arrowheads). (b) Longitudinal section of the vertebral canal from T4 to T12 shows linear, focally extensive to circumferential extradural masses (arrowheads), sometimes around the spinal nerves roots (arrows)

Figure 3

Extramedullary hematopoietic tissue from the epidural location (indicated by the arrowheads in the Figure 2b) with active hematopoiesis characterized mainly by erythroid precursors and megakaryocytes, with fewer myeloid precursors (hematoxylin and eosin)

Figure 4

(a) Cross-section of rib, close to the costochondral junction: extramedullary hematopoietic (EMH) tissue infiltrating and replacing the skeletal muscle on the medial side subpleurally (right side of the image and detailed in [b] [arrow]). Bone marrow is hypercellular (detailed in [c] [arrow]). Hematoxylin and eosin (HE). (b) EMH tissue infiltrating and replacing the intercostal muscles consists primarily of erythroid precursors (similar to Figure 3). A vacuolated fragment of skeletal muscle fiber is also seen (HE). (c) Bone marrow from the rib is hypercellular and contains frequent early myeloid precursors (HE)