Plasma cell myeloma in the horse. A case report and literature review.

This article reports on the infrequent occurrence of plasma cell myelomas in horses, utilizing data from 10 cases to provide a detailed characterisation of the disease in these animals. The cases suggest the condition affects both genders equally and most often occurs in hot-blooded horses, with Quarter Horses being particularly susceptible.

Study Population and Clinical Findings

• The cases studied comprised of equally represented genders of horses, most commonly hot-blooded horses, specifically Quarter Horses. The median age at diagnosis was 11 years, within a range of 3 months to 22 years.
• Key clinical observations included weight loss, anorexia, fever, limb edema, pneumonia, rear leg paresis or ataxia, epistaxis, palpable lymphadenopathy, and bone pain.

Laboratory Findings

• The horses frequently presented with anemia and in three cases, the Red Blood Cells (RBCs) were macrocytic.
• Other variable findings included leukopenia, thrombocytopenia, and circulating plasma cells.
• Abnormalities were seen in protein concentrations and hyponatremia, along with occasional hypocholesterolemia, hypercalcemia, and azotemia.
• Characteristically, but not constantly, there was evidence of hyperproteinemia, hypoalbuminemia, and hyperglobulinemia.

Protein Analysis and Diagnostics

• Monoclonal proteins were detected in the alpha 2, beta, or gamma region through serum electrophoresis. The paraprotein’s heavy chain, evaluated in four horses, was a subclass of IgG. Decreased concentrations of normal immunoglobulins were present in three horses.
• Variable proteinuria was witnessed in four out of six horses. Bence Jones proteinuria was detected in one horse and monoclonal proteins were seen in two others through electrophoresed urine samples.
• Radiographic examination shows lytic bone lesions in three horses. However, bone marrow aspirates were diagnostic only in two out of five horses.

The study’s data thus helps deepen our understanding of plasma cell myelomas in horses, illuminating the clinical and diagnostic characteristics of this infrequently reported disease.