Primary Kidney Lymphoma in a Dog

Background: Lymphoma is a malignant lymphoid tumor originating in the lymph nodes or other solid organs and comprises 90% of all hematopoietic tumors in dogs. However, primary renal lymphoma is rare and is associated with nonspecific clinical signs. Tumor invasion in both kidneys can cause severe clinical signs due to renal failure, complicating the patient's treatment and prognosis. The aim of this case was to report the case of a dog affected by bilateral primary renal lymphoma. In addition, to characterize the clinical and histopathological presentation due to the intense morphological changes. Case:  A 5-year-old male Poodle canine was admitted showing apathy and emesis for 5 days. On physical examination, the dog showed 10% of dehydration, reddish oral mucous membranes, poor body condition (score 1/5), uremic breath, and pain in the kidney area. Complementary tests revealed severe low white blood cells count, high BUN levels, high levels of potassium, calcium, and phosphorus (serum biochemistry). Abdominal ultrasound showed bilateral kidney enlargement. Fine needle aspiration of the mass (guided by ultrasound) revealed round cell tumor. Radiographs showed no alterations. The dog died due to his poor condition and necropsy was performed. On post-mortem examination, the kidneys were both enlarged, pale, and with an irregular subcapsular surface. The histopathological diagnostic was primary renal lymphoma. Immunohistochemical staining revealed that neoplastic cells were strongly positive for anti CD20 and PAX5, while negative for CD3, supporting the diagnosis of B-cell lymphoma. Discussion: The diagnosis was based on clinical, complementary tests, fine needle aspiration, histopathological and immunohistochemical findings. In dogs, primary kidney tumors are uncommon and usually malignant. The presence of vomiting, uremic breath, dehydration, weight loss, and erosive and ulcerative lesions on the tongue (uremic glossitis) are clinical signs of chronic renal failure, and this condition was later confirmed by laboratory tests and histopathological findings. Dogs diagnosed with extra-nodal renal lymphoma, present clinical signs such as polydipsia, polyuria, vomiting, and uremic breath in some cases. These changes are compatible with changes observed in cases of renal failure. In this case, the severe azotemia, hyperphosphatemia, hypocalcemia, and hyperkalemia were due to the neoplastic infiltration in both kidneys. Additionally, the abdominal ultrasound revealed the tumor in both kidneys. Almost 38% of dogs with renal lymphoma presented in urine evaluation normal urine density and a large amount of protein in the urine, similar to those observed in this dog. When the lesions are on both kidneys, kidney failure develops and uremic extra-renal lesions appear, as observed in this case. The prevalence of primary kidney tumors in domestic animals corresponds to less than 1% of the total of the tumors reported, and they are usually in one kidney. In dogs, almost 60 - 70% of lymphomas are B cells, 30 - 40% are T cells, and less than 1% are null cells. B-cell lymphomas usually show less aggressive behavior when compared to T-cell lymphomas. Kidney lymphoma can be included as an important cause of kidney failure, and has slow and progressive development, making early diagnosis and treatment difficult. Keywords: dog disease, lymphoproliferative disorder, renal neoplasm, uremia. Título: Linfoma renal primário em cãoDescritores: doença de cão, distúrbio linfoproliferativo, neoplasma renal, uremia.