Retrospective Study of T Cell Leukaemia (Large Granular Lymphocyte Variant) in Dogs Associated with Suspected Immune-Mediated Cytopaenia(s) in the Absence of Peripheral Lymphocytosis

Simple Summary Large granular lymphocyte leukaemia associated with severe neutropaenia is extremely rare in dogs. A search of the veterinary literature identified only two case reports. The present study included six dogs with this condition. All patients presented with pyrexia and lethargy and had severe neutropaenia on haematology (median neutrophil count 0.07 x 10(9)/L) with no peripheral lymphocytosis. In all dogs, bone marrow cytology revealed infiltration of granular T lymphocytes. All patients received systemic chemotherapy (five received chlorambucil and prednisolone, one received vincristine, cyclophosphamide, and prednisolone); resolution of the neutropaenia was observed within 19 weeks. Two dogs were euthanised 133 and 322 days after diagnosis due to progressive disease, two were lost to follow-up after 224 and 357 days, and two were alive and disease free at 679 and 721 days. The aim of this retrospective study was to describe the clinical characteristics, treatments, and outcomes of dogs with chronic LGL leukaemia with suspected immune-mediated cytopaenia(s) upon presentation. This condition should be considered in the differential diagnosis of patients presenting with severe neutropaenia. Canine chronic large granular lymphocyte (LGL) leukaemia is commonly characterised by moderate to marked lymphocytosis but not neutropaenia. In humans, LGL leukaemia is often associated with autoimmune disorders, including immune-mediated cytopaenias (mainly neutropaenia). This presentation is rare in dogs. The aim of this retrospective study was to describe the clinical characteristics, treatments, and outcomes of dogs with chronic LGL leukaemia with suspected immune-mediated cytopaenia. Six dogs with a median age of 4.5 years (range 2-8 years) were included in the study. The most common presenting signs were pyrexia and lethargy. All dogs had severe neutropaenia (median neutrophil count 0.07 x 10(9)/L), three had thrombocytopaenia (median platelet count 66 x 10(9)/L), and one had anaemia (HCT 0.32 L/L). In all dogs, bone marrow cytology revealed infiltration of granular T lymphocytes; PARR analysis confirmed clonality in four, and bone marrow flow cytometry identified CD3+ CD8+ neoplastic cells in two cases. All patients received systemic chemotherapy, and the cytopaenias resolved after 1-19 weeks. Two dogs were euthanised 133 and 322 days after diagnosis, two were lost to follow-up after 224 and 357 days, and two were alive at 546 and 721 days. A subset of LGL leukaemia in dogs is associated with immune-mediated cytopaenia and has a unique clinical presentation.