Classifying Lymphocytosis in Dogs

ArticleLast Updated March 20093 min read
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This study immunophenotyped cases of lymphoproliferative disorders in dogs presenting with peripheral lymphocytosis. The study population consisted of 202 dogs that had peripheral blood evaluation by flow cytometry in the Clinical Immunology Service at Colorado State University between 2003 and 2005. Where documented, reasons for submission included lymphocytosis on complete blood count; observation of an expanded population of small, mature-appearing cells; and identification of cells with an abnormal structure by the clinical pathologist reviewing the blood smear. Upon initial analysis, 4 main phenotypic classifications were identified: CD21+ (B cell), CD8+ (T cell), CD4-8-5+ T cell (aberrant T-cell phenotype), and CD34+ (undifferentiated progenitor). Expression of CD34+ predicted a poor outcome (median survival, 16 days) compared with other phenotypes. Median survival was as follows: CD21+, 394 days; CD4-8-5+, 289 days; and CD8+, 474 days. Although there was no overall difference in survival between dogs with T-cell and B-cell lymphocytosis, additional features in each of these groups were significantly associated with survival: The CD8+ dogs presenting with lymphocytosis of greater than 30,000/mL had significantly shorter median survival (131 days) than those presenting with less than 30,000/mL (median survival, 1098 days). The difference remained significant after adjustment for treatment. Overall size of circulating lymphocytes predicted outcome in cases of CD21+ lymphocytosis: CD 21+ lymphocytosis composed of predominantly large cells was associated with shorter survival times (129 days) compared with CD21+ lymphocytosis composed of smaller cells (median survival time not reached). Immunophenotype became highly prognostic in the context of lymphocyte size for B-cell disorders and initial lymphocyte count for T-cell disorders. Flow cytometry for classifying lymphoproliferative disorders is advantageous because it is more objective than cytology or histology and may be easier to standardize. The authors conclude that immunophenotyping could provide an objective method for classifying disease and predicting clinical outcome of disorders characterized by lymphocytosis.**COMMENTARY:** The characterization of lymphoma in the dog as either a B-cell or T-cell phenotype has proven prognostic value. It is well established that a B-cell phenotype carries a more favorable prognosis than a T-cell phenotype. In contrast, dogs presenting with neoplastic circulating peripheral lymphocytosis can be a diagnostic and prognostic challenge. These data provide strong evidence that lymphocyte immunophenotype, together with increased lymphocyte size or increased lymphocyte number, correlates with prognosis for dogs with lymphoproliferative disorders involving the peripheral blood. Clinicians can now confidently use flow cytometry, a simple blood test on circulating blood, to provide better prognostic information for a dog with neoplastic circulating lymphocytosis.Canine lymphoproliferative disease characterized by lymphocytosis: Immunophenotypic markers of prognosis. Williams MJ, Avery AC, Lana SE, et al. J VET INTERN MED 22:596-601, 2008.