Page 1306 - Clinical Small Animal Internal Medicine

1244 Section 11 Oncologic Disease

MM produces a biclonal gammopathy. A dog with MM >10% plasma cells in the marrow, especially if cellular
VetBooks.ir may still have a normal globulin level due to suppression atypia or clustering is present, is used to diagnose MM by
some investigators, while the majority agree that >20%
of normal globulin production. Therefore, if findings
support MM, SPE should be done even if total globulin
neoplastic plasma cells varies from normal to large pleo­
level is normal. When monoclonal gammopathy is dem­ plasma cells is a more reliable value. The morphology of
onstrated, immunoelectrophoresis can determine the morphic cells with large cytoplasm, high mitotic index,
antibody type. and multinucleation (Figure 135.4). In cats (and less often
Urinalysis provides information on renal function, uri­ in dogs), bone marrow infiltration may not be severe
nary tract infection, and proteinuria. However, urine enough and visceral organ infiltration may be diagnostic
dipsticks only measure albumin. Special heat precipita­ instead.
tion methods are required to detect Bence Jones pro­ In patients with hypercalcemia, ionized calcium is
teins. This is a qualitative test associated with a high rate indicated for confirmation because binding of calcium to
of false‐positive and ‐negative results in people. Urine paraproteins will increase total calcium while ionized
electrophoresis or immunoelectrophoresis may be more calcium remains normal. Hypocholesterolemia was
reliable. reported in 68% of cats with MM in one study. A possible
Bone involvement may appear on radiographs as mul­ explanation is downregulation of cholesterol production
tiple osteolytic lesions affecting mainly the axial skele­ by the liver to maintain oncotic pressure in the face of
ton, or as diffuse osteoporosis (Figure 135.3). Plain hyperglobulinemia. When HVS is suspected, serum vis­
survey skeletal radiographs are recommended for detec­ cosity can be measured in relation to water. Normal
tion of these lesions. It is best to start with thoracic, lum­ canine serum viscosity is 1.6–1.8 times that of water.
bar spine, and pelvic radiographs, unless pain is localized Clinical signs of HVS usually appear when serum viscos­
to other bones. Skeletal CT can be more sensitive than ity is greater than five times that of water.
radiographs for detection of small lesions and spinal cord Differential diagnoses for monoclonal gammopathy
compression. Radionuclide bone scans are not recom­ include B cell lymphoma, mainly chronic but also acute
mended because MM lesions are primarily lytic and may B cell lymphoid leukemia, WM, chronic infections such
be undetectable. Abdominal ultrasound is recommended as Ehrlichia canis and leishmaniasis in dogs, feline infec­
in all cats and in dogs without bone marrow plasma­ tious peritonitis (FIP) in cats, and monoclonal gammop­
cytosis. Most common abnormalities are splenomegaly, athy of unknown significance (MGUS). The latter is a
hepatomegaly, and changes in echogenicity or nodules in benign process, well recognized in humans but only a
these organs. few cases have been reported in dogs and cats.
Bone marrow aspiration is required for a definitive Diagnosis of EMP and SOP is made by tissue biopsy
diagnosis of MM and is taken from routine sites. In some or fine needle aspirate. Most EMPs are not well
cases, aspiration or a needle core biopsy is taken directly
from a lytic lesion if it is large enough and accessible.
This is especially pertinent in cases of SOP. Normal bone
marrow contains less than 5% plasma cells. Finding of

Figure 135.4 Bone marrow aspirate from a dog with multiple
myeloma showing abundant plasma cells with a typical
Figure 135.3 Lateral radiograph showing well‐demarcated small paranuclear clear zone of the golgi apparatus. A single bincucleate
“punched out” lytic lesions and a “lacy” trabecular pattern in the cell is present (arrow). Source: Courtesy of Dr Sharon Kuzi, Koret
cervical vertebrae due to diffuse osteopenia in a dog with MM. School of Veterinary Medicine, Israel.