Page 1325 - Small Animal Internal Medicine, 6th Edition

CHAPTER 79 Lymphoma 1297

molecularly mediated distant effects of the neoplasm). Para-
neoplastic syndromes that have been encountered in dogs
VetBooks.ir with lymphoma include hypercalcemia, monoclonal and
polyclonal gammopathies, immune-mediated cytopenias
(typically immune-mediated hemolytic anemia or immune-
mediated thrombocytopenia), polyneuropathy, and hypo-
glycemia. Only hypercalcemia and gammopathies have been
documented in cats with this neoplasm, although they are
considerably less frequent than in dogs. Of all these syn-
dromes, humoral hypercalcemia of malignancy in dogs is of
main clinical relevance and typically resolves with the treat-
ment. Most paraneoplastic syndromes resolve when patients
are treated with chemotherapy.
Hematologic and serum biochemical features
A variety of nonspecific hematologic and serum bio-
chemical abnormalities can be detected in patients with
FIG 79.5 lymphoma. The hematologic abnormalities result from
Facial deformity and nasal discharge associated with infiltration of the bone marrow with neoplastic cells,
intranasal lymphoma in a 6-year-old cat. splenic hypofunction or hyperfunction (caused by neoplas-
tic infiltrates), chronic disease, or paraneoplastic immune-
renal and CNS lymphoma in cats, so some oncologists rec- mediated abnormalities. Certain hematologic abnormalities
ommend using antineoplastic drugs that achieve high CNS (i.e., monocytosis, eosinophilia, leukemoid reactions) may
concentrations (i.e., cytosine arabinoside, lomustine) in the result from the local or systemic production of bioactive
treatment of cats with renal involvement in an attempt to substances by the tumor cells (e.g., hematopoietic growth
prevent secondary CNS dissemination (see later). factors, interleukins). With the new flow cytometry (FCM)-
Dogs and cats with neural lymphoma are evaluated based hematology analyzer, neoplastic cells in circulation
because of a variety of neurologic signs that reflect the loca- are often “counted” as monocytes, so monocytosis should
tion and extent of the neoplasm. Although CNS signs are always prompt careful evaluation of the graphics or a blood
most common, peripheral nerve involvement may occur smear review. Given the fact that these analyzers evaluate
occasionally in cats. Three forms of presentation are clini- 10,000 to 15,000 leukocytes per run, it is common to iden-
cally recognized: solitary epidural lymphoma, neuropil tify neoplastic cells in circulation in dogs with lymphoma
(intracranial or intraspinal) lymphoma (also called true CNS (Fig. 79.6).
lymphoma), and peripheral nerve lymphoma. Solitary epi- The serum biochemical abnormalities result from either
dural lymphoma is common in young FeLV-positive cats. the production of bioactive substances by the tumor cells or
Neural lymphomas can be primary (e.g., epidural lym- from organ failure secondary to neoplastic infiltration. In
phoma), or they may be secondary to the multicentric form; general, the complete blood count (CBC) and biochemical
as discussed earlier, secondary CNS involvement may occur profile are not diagnostic in cats and dogs with lymphoma,
in cats with renal lymphoma. Additionally, dogs that have unless there are unclassified cells identified as abnormal lym-
been receiving chemotherapy for multicentric lymphoma phoid cells on evaluation of the blood smear or the graphics
can develop late CNS relapse; these patients develop acute from the analyzer.
onset of neurologic signs, usually while the multicentric neo- Common hematologic abnormalities include nonregen-
plasm is still in remission. This late CNS relapse is likely erative anemia, leukocytosis, neutrophilia (with or without
related to the fact that most drugs used to treat lymphoma a left shift), monocytosis, eosinophilia (usually in cats),
do not cross the blood-brain barrier when used at standard abnormal lymphoid cells in peripheral blood (i.e., leukemic
doses; thus the CNS becomes a sanctuary for tumor cells. In phase of lymphoma), thrombocytopenia, isolated or com-
our clinics, CNS signs in any dog with lymphoma before or bined cytopenias, and leukoerythroblastic reactions, among
during treatment are attributed to this neoplasm (and treated others. Lymphocytosis is rare in dogs and cats with lym-
accordingly) until proven otherwise. phoma; when present, it is usually of low magnitude (i.e.,
A variety of differential diagnoses should be considered <10,000-12,000/µL). Erythrocytosis occurs in approximately
in a dog or cat with suspected lymphoma. The clinician half of the dogs with renal lymphoma, but it is extremely
should always bear in mind that lymphomas are great imita- uncommon in cats (see Chapter 84).
tors; they can mimic numerous different neoplastic and non- Serum biochemical abnormalities are more common in
neoplastic disorders. The differential diagnoses for cats and dogs than in cats with lymphoma and consist mainly of
dogs with lymphoma are similar to those in patients with hypercalcemia or gammopathies. Hypercalcemia is one of
leukemia (see Chapter 80). the most common paraneoplastic abnormalities in dogs with
Occasionally, dogs with lymphoma are evaluated because lymphoma, occurring in approximately 20% to 40% of the
of clinical signs secondary to a paraneoplastic syndrome (i.e., patients; it is extremely rare in cats, and it is more prevalent