Page 465 - Veterinary Immunology, 10th Edition

Myelomas have been described in humans, mice, dogs, cats,
VetBooks.ir horses, cows, pigs, ferrets, and rabbits. They account for less than

1% of all canine tumors, and they are considerably rarer in the other
domestic species. The clinical presentations of myelomas include

bleeding disorders, hyperviscosity, renal failure, and
hypercalcemia. Other signs include lethargy, recurrent infections,
anemia, lameness, bone fracture, and neurological signs, including
dementia and peripheral neuropathy. The most common clinical

manifestation in dogs is excessive bleeding as a result of a
thrombocytopenia and a loss of clotting components as they bind to
myeloma proteins. The presence in serum of abnormally large
quantities of immunoglobulins results in a hyperviscosity

syndrome, which is especially severe in animals with IgM
myelomas (macroglobulinemia). As a result of the increase in blood
viscosity, the heart must work harder, and congestive heart failure,
retinopathy, and neurological signs may result. Because myeloma

cells stimulate osteoclast activity, the presence of tumors in bone
marrow may lead to severe bone destruction. Multiple radiolucent
osteolytic lesions and diffuse osteoporosis develop and are readily
seen by radiography (Fig. 15.22). These lesions result in

pathological fractures. Light chains, being relatively small, are
excreted in the urine. Unfortunately, they are toxic for renal tubular
cells and, as a result, may cause renal failure. The light chains may
be detected by electrophoresis of concentrated urine or, in some

cases, by heating the urine. Light chains precipitate when heated to
60°C but redissolve as the temperature is raised to 80°C. Proteins
possessing this curious property are called Bence-Jones proteins,
and their presence in urine suggests a myeloma. They occur in

about 40% of canine cases. Nonsecretory myelomas are occasionally
diagnosed in dogs (Fig. 15.23).

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