title: Thymoma-associated lymphocytosis in a dog.
abstract: A 9-year-old female spayed English Springer Spaniel was evaluated for a cranial mediastinal mass and lymphocytosis. Flow cytometric immunophenotyping of peripheral blood lymphocytes revealed 97% as CD3 positive, confirming a T-cell lineage. Additionally, T-cell subset assessment showed 53.2% to be double-negative T-lymphocytes, expressing neither CD4 nor CD8 surface markers. The number of double-negative lymphocytes in circulation coincided with the number of T-cell receptor (TCR) γδ-expressing T-cells in circulation. Molecular T-cell clonality analysis of TCR Gamma (TCRG) gene rearrangement showed a polyclonal expansion of T-lymphocytes. Histopathology confirmed the mass to be a thymoma, supporting the diagnosis of thymoma-associated T-cell lymphocytosis. Resolution of the lymphocytosis after removal of the thymoma provided further evidence for this diagnosis. To the authors' knowledge, this case is only the second report of thymoma-associated peripheral lymphocytosis in the veterinary literature, and is the first to report a confirmed thymoma-associated peripheral γδ T-cell lymphocytosis in a dog.
authors.affiliation: Veterinary Medical Teaching Hospital, University of California-Davis, Davis, CA, USA.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Burton
authors.forename: Dori L
authors.initials: DL
authors.lastname: Borjesson
authors.forename: William
authors.initials: W
authors.lastname: Vernau
mesh_terms: D000818:Animals; D004283:Dog Diseases / Q000175:diagnosis* / Q000473:pathology; D004285:Dogs; D005260:Female; D005434:Flow Cytometry / Q000662:veterinary; D007958:Leukocyte Count / Q000662:veterinary; D008218:Lymphocytosis / Q000175:diagnosis / Q000209:etiology / Q000473:pathology / Q000662:veterinary*; D013945:Thymoma / Q000150:complications / Q000175:diagnosis / Q000473:pathology / Q000662:veterinary*; D013953:Thymus Neoplasms / Q000150:complications / Q000175:diagnosis / Q000473:pathology / Q000662:veterinary*
keywords: Flow cytometry; gamma delta T cells; immunophenotyping; molecular clonality testing; polyclonal