Page 1341 - Small Animal Internal Medicine, 6th Edition

CHAPTER 80 Leukemias 1313

characterized by cytopenias and a hypercellular bone marrow TABLE 80.3
and is more common in cats than in dogs. The clinical and
VetBooks.ir hematologic features of dogs and cats with MDS are dis- Clinical Signs and Physical Examination Findings in
cussed at the end of this chapter.
Dogs and Cats With Acute Leukemias*
FINDING DOG CAT
LEUKEMIAS IN DOGS
Clinical Sign
In dogs, leukemias constitute less than 10% of all hemolym- Lethargy >70 >90
phatic neoplasms and are therefore considered rare. At one Anorexia >50 >80
author’s previous clinic, the leukemia-to-lymphoma ratio is Weight loss >30-40 >40-50
approximately 1:7 to 1:10. However, this ratio is artificially Lameness >20-30 >?
high because many dogs with lymphoma may be treated by Persistent fever >30-50 >?
their family veterinarians, whereas most dogs with leukemia
are referred for treatment. Although most leukemias in dogs Vomiting/diarrhea >20-40 >?
are considered to be spontaneous in origin, radiation and Physical Examination Finding
viral particles have been identified as etiologic factors in Splenomegaly >70 >70
some experimental dogs with this disease.
Hepatomegaly >50 >50
Lymphadenopathy >40-50 >20-30?
ACUTE LEUKEMIAS Pallor >30-60 >50-70?
Fever >40-50 >40-60?
Prevalence
In the United States, AML appears to be more common than ?, Unknown.
ALL in dogs, constituting approximately three fourths of the *Results are expressed as the approximate percentage of animals
cases of acute leukemia. However, in two studies from Italy, showing the abnormality.
one reported that ALL was almost twice as common as AML
(Tasca et al., 2009), and the other one reported similar preva- petechiae, ecchymoses, or both. Icterus may also be detected
lence of the two (Novacco et al., 2015a). However, morpho- if marked leukemic infiltration of the liver has occurred.
logically (i.e., as determined by evaluation of a Wright- or The generalized lymphadenopathy seen in dogs with acute
Giemsa-stained blood or bone marrow smear), most acute leukemia is usually mild in contrast to that seen in dogs with
leukemias are initially classified as lymphoid. After cyto- lymphoma, in which the lymph nodes are typically massively
chemical or immunocytochemical staining of the smears, or enlarged (Fig. 80.2). In other words, the hepatosplenomeg-
immunophenotyping is performed, approximately one third aly is more striking than the lymphadenopathy in leukemic
to one half of them are then reclassified as myeloid. Approxi- patients. Most dogs with leukemia also have constitutional
mately half of the dogs with AML have myelomonocytic signs (i.e., they are clinically ill), whereas most dogs with
differentiation when cytochemical staining or immunophe- lymphoma are asymptomatic. Although it is usually impos-
notyping is performed (see Table 80.2). With the advent of sible to distinguish between acute myeloid and ALL on the
immunophenotyping, most laboratories are no longer doing basis of physical examination findings alone, some subtle dif-
cytochemical stains. There is a bimodal age of presentation, ferences do exist; mainly, shifting limb lameness, fever, and
with most diagnosed at 1 to 3 years of age, whereas a small ocular lesions (hyphema, hypopyon) are more common in
proportion develop AL as adults (>7 years). dogs with AML, whereas neurologic signs are more common
in dogs with ALL.
Clinical Features
The clinical signs and physical examination findings in Hematologic Features
dogs with acute leukemia are usually vague and nonspecific Marked hematologic changes are usually present in dogs
(Table 80.3). Most owners seek veterinary care when their with acute leukemia. Couto (1985) and Grindem et al.
dogs become lethargic or anorectic, or when persistent or (1985b) have published detailed reviews of the hematologic
recurrent fever, severe weight loss, shifting limb lameness, or features of dogs with acute leukemia. Briefly, abnormal (leu-
other nonspecific signs develop; neurologic or ocular signs kemic) cells are observed in the peripheral blood of most
occur occasionally. Some of these signs may be quite acute dogs with AML and ALL, although this is slightly more
(e.g., days). Splenomegaly, hepatomegaly, pallor, fever, and common in the latter (i.e., circulating blasts are absent in
mild generalized lymphadenopathy are commonly detected some dogs with AML; Fig. 80.3). Isolated cytopenias, bicy-
during routine physical examination. The spleen in these topenias, or pancytopenia is present in almost all dogs with
dogs is usually markedly enlarged, and it has a smooth AML and ALL. Leukoerythroblastic reactions are detected
surface on palpation. Inspection of the mucous mem- in approximately half of dogs with AML but are rare in dogs
branes in dogs with acute leukemia often reveals pallor and with ALL. The total white blood cell (WBC) and blast counts