Page 1342 - Small Animal Internal Medicine, 6th Edition

1314 PART XII Oncology

are highest in dogs with ALL (median, 298,200/µL; range,
4000-628,000/µL), and as a general rule, only dogs with ALL
VetBooks.ir have WBC counts greater than 100,000/µL. Most dogs with
AML and ALL are anemic, but dogs with acute monoblastic/
monocytic leukemia (AMoL or AML-M 5 ) have the least
severe anemia (packed cell volume of 30% versus 23% in all
other groups). Most dogs with acute leukemias are also
thrombocytopenic, although the thrombocytopenia also
appears to be less severe in dogs with AML-M 5 (median,
102,000/µL; range, 39,000-133,000/µL).
With the advent of automated hematology analyzers
based on flow cytometry and/or impedance, practitioners
have access to “dot plots” or “cytograms” with some instru-
ments. Visualization of dot plots in dogs with acute leuke-
A mias is helpful because some instruments “recognize” these
leukemic cells as lymphocytes or monocytes (the analyzer
“counts” >10,000 cells, whereas we only count 100 cells when
we do a differential leukocyte count), but the shape of the
“cloud” in the cytogram is quite unique (Fig. 80.4). In some
dogs, the numerical values only indicate “monocytosis” or
“lymphocytosis,” but visualization of the dot plots is helpful
from a diagnostic standpoint. In addition, in dogs with high
leukemic cell counts, the abnormal cells may be counted as
reticulocytes by the analyzer; this is important, because the
anemia will then be classified as “regenerative” (Novacco
et al., 2015b). However, all the reticulocytes are located in a
relatively small area, as opposed to being widely distributed,
as in dogs with true regenerative anemia.

B Diagnosis
A presumptive diagnosis in dogs with acute leukemia is
FIG 80.2 usually made on the basis of the history and physical exami-
Hepatosplenomegaly and generalized lymphadenopathy in nation findings; a complete blood count (CBC) is usually
dogs with acute leukemia or multicentric lymphoma. Note confirmatory, although the hematologic changes in dogs
the marked hepatosplenomegaly and mild lymphadenopathy
in the leukemic patient (A) and the marked with “aleukemic leukemia” may resemble those of ehrlichio-
lymphadenopathy and mild hepatosplenomegaly in the dog sis or other bone marrow disorders (e.g., bone marrow
with lymphoma (B). (Artwork by Tim Vojt. Reproduced with aplasia). Interestingly, as discussed earlier, some flow
the permission of The Ohio State University.) cytometry-based hematology analyzers allow for visualiza-
tion of the abnormal cells in the leukocyte graphics (see Fig.
80.4); therefore the term oligoleukemic leukemias may be
more appropriate than aleukemic leukemia.
To evaluate the extent of the disease, a bone marrow aspi-
rate or biopsy may be indicated; if the patient has a high
circulating blast count, a bone marrow aspirate is rarely nec-
essary for diagnosis or prognosis. Splenic, hepatic, or lymph
node aspirates for cytologic evaluation can also be obtained
easily, although the information yielded may not help in
establishing the diagnosis or prognosis. For example, if a
dog has mild generalized lymphadenopathy and the only
sample submitted to a laboratory is a lymph node, spleen,
or liver aspirate, the finding of undifferentiated blasts in the
smear points toward a cytologic diagnosis of either acute
leukemia or lymphoma (i.e., the neoplastic lymphoid cells in
FIG 80.3
Blood smear from a dog with acute lymphoblastic leukemia lymphoma and leukemia are indistinguishable morphologi-
and a white blood cell count of approximately 1 million/µL. cally); indeed, it is quite common for the clinical pathologist
Note the predominance of large, immature lymphoid cells to issue a diagnosis of lymphoma because it is the more
with large nuclei, clumped chromatin, and nucleoli (×1000). common of the two diseases. In these cases, further clinical