Acute Lymphoblastic Leukemia in a Dog

Abstract

Background: Acute lymphoblastic leukemia (ALL) is a rare hematopoietic neoplasm in dogs, characterized by the abnormal proliferation of immature lymphocytes in the bone marrow and peripheral blood. The etiology of ALL is not entirely understood, but environmental and genetic factors are considered contributors. The disease occurs due to abnormal clonal self-replications in the bone marrow, resulting in the proliferation and accumulation of lymphoblasts, which prevent normal hematopoiesis. The clinical symptoms are nonspecific, necessitating differential diagnosis from diseases such as chronic lymphocytic leukemia and grade V lymphoma. Diagnosis is generally based on the identification of lymphoblasts in the bone marrow and peripheral blood, supplemented by tests such as immunophenotyping by flow cytometry. The treatment is not yet fully established, but antineoplastic chemotherapy drugs are commonly used. The prognosis is unfavorable, with rapid progression to death.

Case: A 10-year-old intact male Golden Retriever initially presented for elective orchiectomy. Preoperative tests revealed persistent and progressive leukocytosis. The dog had a history of hemoparasitic infections. During a hematological consultation, the patient showed a body condition score (BCS) of 3/9, normal-colored mucous membranes, normal heart and lung sounds, and normal lymph nodes. A complete blood count (CBC) indicated normocytic normochromic anemia and leukocytosis due to lymphocytosis with atypical lymphocytes. Suspecting lymphoid leukemia, further tests were performed, including a CBC with reticulocyte count, myelogram, PCR for hemoparasitic infections, serology for leishmaniasis, and flow cytometry, confirming T-cell phenotype ALL. Initial treatment included intramuscular injections of nandrolone decanoate and subcutaneous injections of alpha-epoetin to stimulate erythropoiesis. The dog was referred for oncological care, where prednisolone and chlorambucil were prescribed. Despite interventions, the patient became more lethargic and dyspneic, with weight loss and anorexia. A follow-up CBC showed macrocytic normochromic anemia and leukocytosis due to lymphocytosis and neutrophilia. The dog died a few weeks later due to the rapid progression of the disease.

Discussion: This case highlights the complexity of diagnosing and treating ALL in dogs. The nonspecific symptoms, such as lethargy, vomiting, respiratory changes, and weight loss, complicate early diagnosis. The infiltration of neoplastic cells into organs like the spleen, liver, and lymph nodes, leading to splenomegaly, hepatomegaly, and lymphadenopathy, is common but was not observed in this patient. Imaging tests like ultrasound could have provided additional insights. Hematological abnormalities such as leukocytosis due to lymphocytosis and normocytic normochromic anemia are typical of ALL. Immunophenotyping by flow cytometry was crucial for diagnosis, distinguishing ALL from other lymphoproliferative conditions. Treatment with nandrolone decanoate and alpha-epoetin did not improve anemia, and palliative chemotherapy with chlorambucil and prednisolone did not halt the disease's rapid progression. The poor outcomes, even with chemotherapy, underscore the need for more effective therapeutic strategies. The average survival for dogs with ALL is 25 to 50 days, aligning with the observed progression in this case. Without treatment, survival is less than 2 weeks, highlighting the grim prognosis.

Keywords: canine, immunophenotyping, neoplasm, chemotherapy.

Título: Leucemia linfoblástica aguda em cão

Descritores: canino, imunoterapia, neoplasia, quimioterapia.