Intravascular Lymphoma in Canine - Clinical, Pathological and Immunohistochemical Aspects

Abstract

Background: Intravascular lymphoma (IL) is a rare disease characterized by presence of neoplastic lymphocytes in the lumen of blood vessels. Any tissue can be affected; however, the most frequently compromised areas of the body are the skin and the central nervous system (CNS). The clinical signs and macroscopic alterations caused by IL are nonspecific and are usually secondary to a continuous proliferative disorder, which leads to occlusion of the blood vessels with consequent thrombosis, hemorrhage and infarction. The objective of this work is to report a case of IL in a dog.Case: An 8-year-old male Rottweiler dog was referred to the Veterinary Hospital of the Federal University of Paraná with a history of cerebellar ataxia that had not improved after treatment. At the neurological examination, cerebellar ataxia and deficit of nasal reflex were detected. A complete blood count showed presence of slight anemia (4.8 million red blood cells/mm3; normal ranges= 5.5-8.5 million/mm3) and thrombocytopenia (176.000/mm3; normal ranges= 250.000-500.000/mm3). Biochemical tests revealed a small increase in alanine aminotransferase (42 IU/L; normal ranges= 14-38 IU/L) and a slight decrease in alkaline phosphatase (49 IU/L; normal ranges= 90-170 IU/L). The cerebrospinal fluid (CSF) exhibited an increased protein concentration (147.3 mg/dL; normal ranges= 18-44 mg/dL) and pleocytosis (8 cells/µL; normal ranges= up to 5 cells/µL). No alterations were observed at radiographic and ultrasonographic exams. A clinical treatment was prescribed; however, in view of the worsening of the clinical signs, euthanasia was performed, and the body was submitted to a Laboratory of Pathology. At necropsy, moderate multifocal ulcers were observed in the oral cavity and ventral side of the tongue; moderately infarcted areas were detected in the spleen. Additional alterations such as fatty liver degeneration, glomerulonephritis, and pulmonary edema were also observed. Consequently, fragments from various tissues were collected, fixed in 10% formaldehyde, and processed for paraffin embedding and microtomy. Sections with a thickness of 5 µm were cut, and stained with hematoxylin and eosin. Microscopically, the cerebral cortex exhibited a marked number of round neoplastic cells with well-defined edges and scant cytoplasm filling the vascular lumen. Similar cells were observed in the lumen of the blood vessels in the cerebellum, spinal cord, liver, lungs, kidneys, and mucocutaneous junction. The cerebellum, mucocutaneous junction, and kidneys were submitted to immunohistochemical evaluation. The results were consistent with T cell lymphoma in the telencephalon, in the mucocutaneous junction, and in the cerebellum; however, the neoplastic cells observed in the kidneys were not positively stained by the antibodies used.Discussion: Since, in this neoplasia, there is no formation of solid tumors as in other lymphomas, the diagnosis is more difficult both clinically and macroscopically, and hence a combination of immunohistochemistry and microscopy are indispensable. Immunohistochemistry for detection of the markers CD3, CD45RA, CD20, PAX5 and CD79a was essential to determine the cell type especially in the mucocutaneous junction, telencephalon, and cerebellum. Absence of staining for any of these markers on the neoplastic cells in the kidneys may be associated with a high degree of cellular undifferentiation, which worsens the prognosis. This case report highlights the importance of the combination of histopathological and immunohistochemical examinations with laboratory tests and the clinical picture of the animal for the diagnosis of this neoplasia, which can be difficult to identify.