T-cell lymphocytic leukaemia and lymphoma in a horse (abstract).

A 10-year-old Thoroughbred gelding showed rapid weight loss over about 1 week. Clinically, it had increased respiration and heart rates, dark red mucous membranes with petechial haemorrhages, and a bilateral keratitis. Routine haematological examination showed a lymphocytosis with increased numbers of small hyperchromatic lymphocytes in circulation, but no anaemia. On necropsy, many enlarged abdominal lymph nodes were seen and there was a large amount of fluid in the peritoneal cavity and pericardial sac. Histopathologically, small lymphocytes in- filtrated most tissues including the bone marrow, lymph nodes, liver, gastrointestinal tract and cornea. These were identified as T-lymphocytes by the use of immunohistochemistry and CD3 (positive), CD20 (negative) and CD 79a (negative) markers. A T-cell lymphocytic leukaemia and multi-centric lymphoma with generalised tissue infiltration were therefore diagnosed.