Marked paraneoplastic basophilia accompanying eosinophilia in a cat with alimentary T-cell lymphoma

CASE SUMMARY A 5-year-old male neutered domestic shorthair cat was referred with a history of persistent pyrexia, pica, soft faeces, inappetence, intermittent vomiting, mild-to-moderate granulocytosis and mild hypercalcaemia. No significant improvement was noted after antibiotic and corticosteroid treatment, except that the hypercalcaemia resolved. Physical examination, including thoracic auscultation, and abdominal and peripheral lymph node palpation, were unremarkable. On admission, haematology revealed moderate leukocytosis (36.8 × 109/l) with moderate-to-marked eosinophilia (21.3 × 109/l) and marked basophilia (4.04 × 109/l), the latter identified microscopically. Lymphocytes were markedly decreased (0.37 × 109/l). Blood smear examination revealed 58% eosinophils, 28% neutrophils, 11% basophils, 2% monocytes, 1% lymphocytes and marked, diffuse platelet clumping. Biochemistry abnormalities indicated mild pancreatitis, dehydration and anorexia with mildly increased pancreatic lipase, mild hypernatraemia (157 mmol/l), a moderate decrease in urea (3.1 mmol/l) and a slight decrease in phosphate (1.32 mmol/l). Ultrasound and radiographic imaging revealed enlargement of the mesenteric lymph nodes. Fine-needle aspiration, a Tru-cut biopsy and immunohistochemistry were performed. Cytological examination revealed ~65-75% lymphocytes (~80% were larger than a neutrophil), ~25-35% eosinophils and occasional basophils. Lymphocytes had single, small (<1/3 red blood cells), prominent nucleoli and increased pale, mildly vacuolated cytoplasm. On histopathology, cells were monomorphic, large, with prominent nucleoli, and mild, multifocal, staining for T-cell marker CD3. Smaller cells were strongly CD3-positive. Cells were negative for B-cell marker CD45R. RELEVANCE AND NOVEL INFORMATION This is the most severe case of paraneoplastic basophilia reported with feline alimentary T-cell lymphoma with accompanying eosinophilia and lymph node infiltration. Feline basophil prevalence is reported for the first time.