• Open Access

Differentiation of Chronic Lymphocytic Leukemia in the Horse: A Report of Two Cases


Oregon State University, College of Veterinary Medicine, Magruder Hall 105, Corvallis, OR 97331


Chronic lymphocytic leukemia (CLL) was diagnosed in two horses: an 18-year-old Quarter Horse gelding that was examined because of edema of the prepuce and ventral abdomen; and a 20-year-old mixed breed gelding that was referred because of lymphocytosis, ventral edema, and weight loss. The first horse had enlarged peripheral lymph nodes and cool nonpainful pitting edema of the ventral abdomen and prepuce. The second horse had enlarged peripheral lymph nodes, cool nonpainful pitting edema of the ventral thorax and cranial ventral abdomen, and a 3/5 holosystolic heart murmur. The diagnosis of CLL was based on increased blood lymphocyte counts and infiltration of marrow and other tissues by lymphocytes. In horse 1, the lymphocytosis persisted for 2 months between initial examination and death. The results of flow cytometric analysis on blood lymphocytes using anti-lymphocyte antibodies suggested that horse 1had T-cell CLL, and horse 2 had B-cell CLL. In addition, the second horse had a monoclonal gammopathy (IgC), with light-chain proteinuria. (Journal of Veterinary Internal Medicine 1992; 6: 225–229)