Page 1286 - Clinical Small Animal Internal Medicine

1224 Section 11 Oncologic Disease

Western Europe. Ninety‐five percent of CLL in people
VetBooks.ir are B cell in origin. ALL is most common in young
children (peak between 2 and 5 years) with a second peak
in aged populations and is most commonly B cell. The
true incidence of lymphocytic leukemias in animals is
unknown. CLL is thought to be less common than ALL
but more common than myeloproliferative disorders.

Signalment
In the dog, both ALL and CLL are most commonly seen
in middle‐aged to older animals with a median age of 10
years. No sex predilection has been found. Golden
retrievers and German shepherds are overrepresented in
CLL. CLL is rare in cats but seems to occur in elderly
cats with a mean age of 14 years. Cats with ALL are usu­
ally young and FeLV positive.

History and Clinical Signs

Most CLL animals are asymptomatic and the diagnosis is Figure 133.1 Photomicrograph of lymphocytes in the peripheral
incidental. When clinical signs are present, they are gen­ blood of a dog that has CLL. The lymphoid morphology is
erally attributable to the degree of lymphocytosis, bone predominantly small and well differentiated. Wright Giemsa stain,
marrow involvement or other organ involvement and 1000× magnification. Source: Courtesy of Dr Jan Andrews, Antech
may include lethargy, inappetence, and weight loss. Diagnostics.
Physical exam may show hepatosplenomegaly and mildly
enlarged peripheral lymph nodes. Clinical signs of ALL marked splenic proliferation or infiltration of granular
patients are similar to CLL although they are typically lymphocytes with minimal bone marrow involvement.
more severe. On physical exam, splenomegaly is the Other staging tests commonly recommended include
most common finding but hepatomegaly and lymphad­ thoracic radiographs, abdominal ultrasound, and subse­
enopathy can also be present. Signs of life‐threatening quent aspirate and cytology of any enlarged organ.
cytopenias such as pale mucous membranes, pyrexia, Immunophenotyping of blood, bone marrow or cytology
and/or petechial hemorrhages are also possible. samples generally reveals the presence of a T cell lym­
phocyte population with no evidence of CD34 expression
(early hematopoietic stem cell marker), confirming the
Diagnosis
maturity of the lymphocytes in question. The presence of
Diagnosis of CLL is commonly made by examination of 30% or more lymphoblasts in the bone marrow is consid­
the peripheral blood and bone marrow by a clinical ered diagnostic for ALL. Lymphoblasts are intermediate‐
pathologist. A complete blood count (CBC) generally to‐large sized lymphocytes with moderate amounts of
reveals an absolute mild to marked lymphocytosis (6000 basophilic cytoplasm. Lymphoblasts are larger than neu­
to >100 000 lymphocytes/μL) and cytologically the nuclei trophils, have a condensed nuclear chromatin pattern,
appear small and mature with condensed chromatin and have a high nuclear to cytoplasmic ratio (Figure 133.2).
(Figure 133.1). Staging tests recommended for ALL are similar to
Other common hematologic findings include a mild CLL; however, one of the principal goals is to differenti­
normochromic, normocytic, nonregenerative anemia, a ate ALL from stage V lymphoma by degree of blood and
mild thrombocytopenia (>100 000/μL), and rarely neu­ bone marrow involvement, lack of significant lymphade­
tropenia. The hematologic abnormalities associated with nopathy and, most importantly, its immunophenotypic
feline CLL have not been well characterized although characteristics. Patients with stage V lymphoma can have
they are thought to be similar to dogs. A monoclonal a better prognosis since their disease does not originate
gammopathy or hyperglobulinemia in cats has been in the bone marrow. Immunophenotyping, especially
reported but is uncommon since most CLL are T cell in flow cytometry, can be very useful in these cases
origin. Bone marrow aspirates show a significant prolif­ because ALL patients will be CD34+, confirming an early
eration of small mature lymphocytes (usually >30%) hematopoietic origin. Both stage V lymphoma and CLL
except in granular T‐CLL which demonstrates a patients will be negative for this marker.