Page 1304 - Clinical Small Animal Internal Medicine

1242 Section 11 Oncologic Disease

dysfunction. Thrombocytopenia and neutropenia may
VetBooks.ir also occur.
Suppression of normal immunoglobulin production is
common and is suggested to result from normal feed­
back inhibition induced by the monoclonal gammopa­
thy. In people, maturation of normal B cells to plasma
cells is suppressed as well as T helper cell number and
function. These abnormalities can lead to immunosup­
pression and, combined with neutropenia, increased risk
for bacterial infections.
Osteolytic bone lesions are induced by secretion
of osteoclast‐activating factors from the bone marrow
microenvironment and myeloma cells. These factors
include the cytokines interleukin (IL)‐1 beta, tumor
necrosis factor (TNF)‐beta, and IL‐6. Osteolytic lesions Figure 135.1 Oral extramedullary plasmacytoma in the maxilla of
a dog.
may cause pain, lameness, spinal compression due to
extradural tumor masses, or vertebral fractures which can
lead to paresis or paralysis. Lytic bone lesions are detected Other sites such as gastrointestinal, trachea, larynx, eye,
in 50–60% of dogs with MM. In cats, skeletal involvement genitalia, and others are rare and comprise 1% of all EMP
is more variable, noted to occur in 8% of cases in one case cases. Cutaneous, oral, and colorectal EMPs are usually
series and in up to 58–67% in other reports. benign but can be locally invasive and cause bone destruc­
Hypercalcemia occurs in 15–20% of dogs and 9–25% of tion in the oral cavity. In humans, cutaneous EMP is
cats with MM. Hypercalcemia was present in 50% of dogs uncommon and is often part of a multicentric disease. In
with MM at diagnosis when ionized calcium rather than dogs, MM rarely exhibits cutaneous involvement. Fewer
total calcium was measured. The main proposed mecha­ reports exist regarding solitary EMP in cats but their
nism is direct bone osteolysis, although skeletal lytic lesions behavior and site distribution appear similar to dogs. The
are more common than hypercalcemia. Hypercalcemia multicentric EMP as part of MM is more common in cats
may be worsened by concurrent renal disease. than dogs although incorporating abdominal ultrasound
Renal disease is one of the serious complications of and cytology into the staging of MM may prove abdomi­
MM, reported in 30–50% of dogs and about 25% of cats. nal organ involvement is more common than previously
Light chains that are filtered by the glomerulus precipi­ thought. A recent study showed that 57% of dogs with
tate in the renal tubule, causing interstitial nephritis. MM that underwent abdominal ultrasound were cyto­
Hypercalcemia, infiltration of the kidneys by myeloma logically confirmed to have liver, spleen, or abdominal
cells, decreased renal blood flow secondary to hypervis­ lymph node involvement. Amyloid deposits of immuno­
cosity, amyloidosis, glomerulonephritis, and pyelone­ globulin origin occur in 3–13% of EMPs.
phritis following immunosuppression may also Solitary osseous plasmacytomas have been reported in
contribute to renal dysfunction. the dog affecting the appendicular skeleton, zygomatic
Cardiac disease, a less common complication, may be arch, and vertebrae. In humans (and probably in dogs),
explained by increased peripheral vascular resistance, the prognosis is much better than for MM but about 50%
excessive cardiac workload, and myocardial hypoxia sec­ of SOPs will eventually develop into MM.
ondary to hyperviscosity.
Waldenström macroglobulinemia is a rare disease in
animals and is considered a form of lymphoplasmacytic Epidemiology
lymphoma involving the spleen, lymph nodes, and bone
marrow along with serum IgM‐related signs of hypervis­ Multiple myeloma is uncommon in both dogs and cats,
cosity or cryoglobulinemia. Osteolytic bone lesions and representing less than 1% of all malignancies. It com­
hypercalcemia are not present and Bence Jones protein­ prises about 8% of all hematopoietic tumors and 3.6% of
uria is uncommon. all primary and secondary bone tumors in dogs. The
Solitary PCD include EMP and SOP. They are defined incidence in both species is lower than in humans.
as local accumulation of neoplastic monoclonal plasma
cells without evidence of systemic PCD. Canine EMPs
are distinct, usually solitary tumors unrelated to MM. Signalment
The skin, especially the head, and extremities are affected
most commonly, followed by the mucous membranes of Multiple myeloma affects older animals with a median age
the oral cavity (Figure 135.1) and the colorectal junction. of 8–9 years (range, 2–15) in dogs and 12–14 years in cats