Page 765 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 33 Hematopoietic Tumors 743

“Normal” immunoglobulin concentrations are often severely
depressed in affected animals. 764 In addition, leukopenia may be
present secondary to myelophthisis. Reports of multiple concur-
VetBooks.ir rent infections in both dogs and cats affected with MM exist and,
in one dog with several concurrent infections, a polyclonal and a
monoclonal gammopathy existed pretreatment, with the former
persisting after successful treatment of the myeloma. 772,773
Variable cytopenias may be observed in association with
MM. A normocytic, normochromic, nonregenerative anemia is
encountered in approximately one-half to two-thirds of dogs with
MM. 757,761–764 This can result from marrow infiltration (myelo-
phthisis), blood loss from coagulation disorders, anemia of chronic
disease, or increased erythrocyte destruction secondary to high
serum viscosity. Rare erythrophagocytic forms of MM have also
been reported in both dogs and cats and may contribute to ane-
mia. 823–825 Similar factors lead to thrombocytopenia and leukope-
nia in 30% and 80% of dogs with MM, respectively; and in cats,
approximately two-thirds, one-half, and one-third will be anemic,
thrombocytopenic, and neutropenic, respectively. 761,762,767,769–771
Cardiac disease, if present, is usually a result of excessive cardiac
workload and myocardial hypoxia secondary to hyperviscosity.
Myocardial infiltration with amyloid and anemia may be com-
• Fig. 33.27 Multiple retinal hemorrhages on the fundus in a cat with hyper- plicating factors. Nearly one-half of cats with MM in two reports
viscosity syndrome secondary to multiple myeloma. presented with a cardiac murmur, the etiology of which was not
established. 767,769 Three cats with HVS presented with congestive
has been reported in cats with IgG-, IgA-, and IgM-secreting heart failure, murmurs, and echocardiographic signs consistent
tumors. 764,765,813–818 In several of these cases, relative serum vis- with hypertrophic cardiomyopathy. 813
cosity was increased above control ranges.
Renal disease is present in approximately one-quarter to one-
half of dogs with MM, and azotemia is observed in 30% to 40% History and Clinical Signs
of cats. 757,761,763,767,769,771 The pathogenesis of renal failure is often Clinical signs of MM may be present up to a year before diagnosis
multifactorial and can ensue as a result of Bence Jones (light-chain) with a median duration of 1 month reported in dogs. 757,764 In
proteinuria, tumor infiltration into renal tissue, hypercalcemia, one cat, M-component elevations were detected 9 years before
amyloidosis, diminished perfusion secondary to HVS, dehydration, clinical presentation. 767 In this latter case, the M-component
or ascending urinary tract infections. 757,764,806,807 Normally, heavy- elevation was consistent with monoclonal gammopathy of
and light-chain synthesis is well balanced in nonneoplastic immu- unknown significance (MGUS). MGUS (i.e., benign, essential,
noglobulin production. In the case of MM, an unbalanced excess or idiopathic monoclonal gammopathy) is a benign monoclonal
of light-chain products may be produced. Light chains are of low gammopathy that is not associated with osteolysis, bone marrow
molecular weight and are normally filtered by the renal glomerulus, infiltration, or Bence Jones proteinuria. MGUS has also been
and their presence in urine can result in protein precipitates and reported in dogs. 826,827 Signs of MM can be variable based on
subsequent renal tubular injury. The presence of light chains in urine the wide range of pathologic effects possible. Tables 33.14 and
without a concomitant monoclonal spike in serum, although rare, is 33.15 list the relative frequencies of clinical signs observed in the
indicative of pure light-chain disease. 802 Tubules become obstructed dog and cat, respectively, based on a compilation of several rep
by large laminated casts containing albumin, immunoglobulin, orts. 757,761,762,764,767,769–771,788 Bleeding diathesis is usually rep-
and light chains. Bence Jones proteinuria occurs in approximately resented by epistaxis and gingival bleeding. Funduscopic abnor-
25% to 40% of dogs with MM. 757,763,764 Bence Jones protein- malities may include retinal hemorrhage (see Fig. 33.27), venous
uria is reported to occur in approximately 40% of cats with MM/ dilatation with sacculation and tortuosity, retinal detachment,
MRD. 767,768 Hypercalcemia is reported in 15% to 50% of dogs and blindness. 757,761,6,764,769,771,808–812 CNS signs may include
with MM and is thought to result primarily from the production of dementia, seizure activity, tremors, and deficiencies in midbrain
osteoclast-activating factor by neoplastic cells. 757,761,762,764,819 Other or brainstem localizing reflexes secondary to HVS or extreme
factors, including increased levels of various cytokines, TNF-α, IL-1, hypercalcemia. Signs reflective of transverse myelopathies second-
and IL-6, have been implicated in human MM. In two dogs with ary to vertebral column infiltration, pathologic fracture, or extra-
MM and hypercalcemia, serum elevations in circulating N-terminal dural mass compression can also occur. 757,764,799,828,829 One case
parathyroid hormone-related peptide were noted. 820 Hypercalcemia of ataxia and seizure activity in a dog with EMP secondary to
may also be exacerbated by associated renal disease. Hypercalcemia, tumor-associated hypoglycemia has been reported. 830 In addition,
initially thought to be a rare event in cats with MM, occurred in paraneoplastic polyneuropathy has been reported in a dog with
10% to 25% of recently reported cases. 767,769–771,821 MM. 831 A history of chronic respiratory infections and persis-
Susceptibility to infection and immunodeficiency have long tent fever may also be present in cats. Hepatosplenomegaly and
been associated with MM and are often the ultimate cause of renomegaly can occur due to organ infiltration. Bleeding diathesis
death in affected animals. 757,764,788 Infection rates in humans due to HVS is less common in the cat; however, epistaxis, pleu-
with MM are 15 times higher than normal and usually present as ral and peritoneal hemorrhagic effusions, retinal hemorrhage,
pneumonia or urinary tract infections. 822 Response to vaccination and central neurologic signs have been reported in both dogs
has also been shown to be suppressed in humans with MM. 822 and cats. 761,764,765,769,813–818 Polydipsia and polyuria can occur