Peripheral Blood Lymphocytosis without Bone Marrow Infiltration in a Dog with T-Zone Lymphoma

Abstract

A 13-year-old neutered male mixed-breed dog presented with generalized lymphadenopathy and erythematous cutaneous lesions in the ear pinnae. Fine-needle aspiration cytology of the lymph nodes revealed small to intermediate lymphocytes with a “hand mirror” configuration as the predominant cell type. Histopathological analysis of the lymph node showed an infiltrate of CD3-positive small lymphocytes compressing the follicles against the capsule owing to neoplastic cell expansion. Flow cytometric analysis revealed a homogeneous population of CD3+/CD4–/CD5+/CD8–/CD21+/CD34–/CD45– cells in both the peripheral blood and aspirated lymph nodes, which supports the diagnosis of T-zone lymphoma. Laboratory tests revealed lymphocytosis (14,144 cells/μL) in the peripheral blood. However, contrary to expectations, the bone marrow examination revealed no evidence of lymphocytic infiltration. T-zone lymphoma is an indolent lymphoma with a long survival period, and knowledge of its characteristics may affect disease staging and prognosis evaluation. Therefore, peripheral blood count as a sole screening tool for bone marrow metastasis should be used with caution. © The Korean Society of Veterinary Clinics.