Plasma cell myelomas in horses have been reported infrequently. Data from 10 cases, 9 from the literature and 1 new case, are used to characterize the disease in the horse. Hot-blooded horses (7/10), specifically Quarter Horses (4/10), were most often affected. Median age at diagnosis was 11 years (range, 3 mo-22 yr) and both male (5) and female horses (5) were represented equally. Clinical findings included
weight loss (6/8),
anorexia (4/8),
fever (4/8), limb
edema (4/8),
pneumonia (3/8), rear leg
paresis/
ataxia (3/8),
epistaxis (3/8), palpable
lymphadenopathy (2/8), and bone
pain (2/8).
Anemia (8/8) was present routinely, and in three horses, RBCs were macrocytic.
Leukopenia (2/8),
thrombocytopenia (2/8), and circulating plasma cells (3/8) were variable findings. Except for abnormal
protein concentrations and
hyponatremia (3), abnormal results from serum biochemical analysis including hypocholesterolemia (1),
hypercalcemia (1), and
azotemia (1) were reported infrequently. Hyperproteinemia (8/9),
hypoalbuminemia (7/9), and hyperglobulinemia (8/9) were characteristic but not invariable findings. Monoclonal
proteins (7/7) were detected in the alpha 2, beta, or gamma region by serum electrophoresis. The
paraprotein's heavy chain, determined in four horses, was a subclass of
IgG. Three horses had decreased concentrations of normal
immunoglobulins. Variable
proteinuria (trace to 4+) was detected by routine urinalysis in four of six horses. Bence Jones
proteinuria was detected in one of five horses (heat precipitation) and monoclonal
proteins were detected in two of three electrophoresed urine samples. Three of the horses had lytic bone lesions detected radiographically. Bone marrow aspirates were diagnostic in two of five horses.(ABSTRACT TRUNCATED AT 250 WORDS)