Page 1413 - Small Animal Internal Medicine, 6th Edition

CHAPTER 86 Combined Cytopenias and Leukoerythroblastosis 1385

have been ruled out, a therapeutic trial of immunosuppres- dogs that were evaluated, that classification scheme is of
sive doses of corticosteroids (with or without other immu- questionable clinical relevance.
VetBooks.ir nosuppressive drugs; see Chapter 72) may be warranted. erature. More than 80% of cats in whom the FeLV status was
Several reports of MDS in cats have appeared in the lit-
Anabolic steroids and erythropoietin do not appear to be
investigated were found to be viremic. Most cats were evalu-
beneficial in these patients.
ated because of nonspecific clinical signs such as lethargy,
Myelophthisis weight loss, and anorexia. Other signs, such as dyspnea, recur-
Infiltration of the BM with neoplastic or inflammatory cells rent infections, and spontaneous bleeding, were observed in a
can lead to the crowding out of normal hematopoietic pre- few cats. Physical examination revealed hepatosplenomegaly
cursors and therefore the development of peripheral blood in more than half of the cats; generalized lymphadenopathy
cytopenias. Disorders resulting in myelophthisis are listed in and pyrexia were detected in approximately one third. In my
Box 86.1. Often these animals are evaluated because of experience, secondary myelodysplasia associated with infec-
anemia, although fever and bleeding caused by neutropenia tious, inflammatory, or immune-mediated diseases is quite
and thrombocytopenia, respectively, can also be presenting common in cats, so a cytologic diagnosis of MDS should be
complaints. The presence of hepatomegaly, splenomegaly, or interpreted with caution (i.e., it is not always a “death sen-
lymphadenopathy in a dog or cat with anemia or combined tence”), and a search for comorbidities should be conducted.
cytopenias is highly suggestive of some of the neoplastic or Hematologic abnormalities in cats with MDS are similar
infectious disorders listed in Box 86.1. to those seen in dogs; they include isolated or combined
A definitive diagnosis in dogs and cats with myelophthisis cytopenias, macrocytosis, reticulocytopenia, metarubricyto-
is obtained by evaluating the cytologic or histopathologic sis, and macrothrombocytosis. Morphologic changes in the
characteristics of a BM specimen. Given the fact that certain BM include a normal to increased cellularity, less than 30%
neoplastic or granulomatous disorders can show a patchy or blasts, an increased myeloid-to-erythroid ratio, dyserythro-
multifocal distribution, the findings yielded by a BM core poiesis, dysmyelopoiesis, and dysthrombopoiesis. Megalo-
biopsy specimen are usually more reliable than those yielded blastic RBC precursors are common, with occasional
by an aspirate. Once a cytologic or histopathologic diagnosis binucleated, trinucleated, or tetranucleated rubricytes or
is obtained, treatment is aimed at the primary neoplasm (i.e., metarubricytes. The morphologic abnormalities in the
with chemotherapy) or infectious agent (see specific sections myeloid cell line include giant metamyelocytes and asyn-
for detailed discussion). chronous nuclear-cytoplasmic maturation.
Acute leukemia subsequently developed within weeks to
MYELODYSPLASTIC SYNDROMES months of the diagnosis in approximately one third of cats
Myelodysplastic syndromes (MDSs) include a host of hema- with MDS described in the literature. MDS commonly pro-
tologic and cytomorphologic changes that may precede the gresses to AML in humans, with only isolated reports of
development of acute leukemias by months or years; in progression to acute lymphocytic leukemia (ALL). However,
humans, they are associated with specific molecular genetic according to Maggio et al. (1978), in one series of 12 cats
changes. In addition to the morphologic abnormalities in with MDS, ALL subsequently developed in 9. This may
blood and BM, functional abnormalities of granulocytes reflect the fact that cytochemical staining was not done to
and platelets have been documented in humans with MDS. classify the leukemic cells, and cells were thus morphologi-
Therefore recurrent infections, spontaneous bleeding ten- cally classified as lymphoid when they were myeloid.
dencies, or both are common in these patients, even when However, because all the cats that showed progression to
the neutrophil and platelet counts are within normal limits. ALL were also viremic with FeLV, the hematologic changes
These abnormalities have also been observed in cats with preceding the development of leukemia did not reflect a
MDS. “spontaneous” hematologic disorder (as seen in human
MDS has been recognized in dogs and cats but appears beings and dogs) but were rather a manifestation of the
to be more common in retrovirus-infected cats. In dogs, morphologic and functional changes induced by FeLV.
clinical signs are nonspecific and include lethargy, depres- The management of dogs and cats with MDS is still
sion, and anorexia. Physical examination findings include controversial. A variety of treatments have been used in
hepatosplenomegaly, pallor, and pyrexia; hematologic humans with MDS, but none has proved effective. Chemo-
changes include pancytopenia or bicytopenia, macrocytosis, therapy, supportive therapy, anabolic steroids, inductors of
normoblastemia, and reticulocytopenia. Acute myelogenous differentiation, hematopoietic growth factors, and andro-
leukemia (AML) subsequently developed 3 months after the genic steroids, among others, have been reported to be of
initial diagnosis of MDS in one patient (Couto et al., 1984). benefit in some humans with MDS. Currently, the preferred
The cytologic BM abnormalities were similar to those approach in humans is treatment with supportive therapy
described in cats (see later). Some authors have proposed and inductors of differentiation or hematopoietic growth
classifying dogs with primary MDSs into those with refrac- factors. Because most patients are older, chemotherapy does
tory anemia and those with true myelodysplasia, following not constitute the first treatment option, given its toxicity. I
similar classification schemes used in humans. However, recommend supportive therapy (e.g., fluids, blood compo-
because almost no clinical information was provided for the nents, antibiotics) and low-dose cytosine arabinoside as an