Differentiation of chronic lymphocytic leukemia in the horse. A report of two cases.

This research investigated two cases of chronic lymphocytic leukemia (CLL) in horses – an 18-year-old Quarter horse and a 20-year-old mixed breed – both diagnosed based on increased blood lymphocyte counts and lymphocytes infiltrating various tissues.

Case Presentations

• The first case was an 18-year-old Quarter Horse gelding. The horse had been medically evaluated due to the presence of edema (excess watery fluid) in the prepuce (skin covering the tip of the penis) and the ventral (front facing) abdomen. The horse exhibited symptoms like enlarged peripheral lymph nodes – a sign of abnormal immune response – and cool, nonpainful, pitting edema in the ventral abdomen and prepuce. Pitting edema is characterized by a dent remaining on the skin after pressing the area.
• The second case involved a 20-year-old mixed breed gelding. The horse was referred for medical attention due to lymphocytosis (an abnormal increase in the number of lymphocytes in the blood), ventral edema, and weight loss. The horse also had enlarged peripheral lymph nodes, cool nonpainful pitting edema in the ventral thorax (chest area) and the cranial ventral abdomen (front part of the belly), and a 3/5 holosystolic heart murmur. A holosystolic murmur is a heart sound that occurs throughout the systole phase (contraction phase) of the heart’s rhythm, signifying a possible heart condition.

Diagnosis and Analysis

• The diagnosis of CLL in both horses was established based on increased blood lymphocyte counts and the infiltration of lymphocytes in the marrow and other tissues. Lymphocytes are an integral part of the immune system and their abnormal presence in high amounts in various tissues indicates a disease.
• In the first horse, this elevated lymphocyte count persisted for two months from the initial examination until its death.
• To further understand the condition, the researchers used flow cytometric analysis on the blood lymphocytes. This is a technology that helps in cell counting, cell sorting, and biomarker detection.
• The results suggested that the first horse had T-cell CLL – a type of blood cancer disrupting the normal, healthy functioning of the T lymphocytes in the immune system. The second horse, on the other hand, was found to have B-cell CLL, a similar cancer type affecting the B lymphocytes.
• Additional findings revealed that the second horse had a monoclonal gammopathy of the IgG type. In this condition, an abnormal number of identical plasma cells (derived from B cells) produce the same immunoglobulin (IgG in this case). The condition was also accompanied by light-chain proteinuria, a condition where parts of antibodies, specifically light chains, are found in urine, indicating a potential kidney issue.