Page 1407 - Small Animal Internal Medicine, 6th Edition

CHAPTER 85 Leukopenia and Leukocytosis 1379

BOX 85.6 BOX 85.7
VetBooks.ir Causes of Lymphopenia in Cats and Dogs Causes of Lymphocytosis in Cats and Dogs

Corticosteroid or Stress-Induced Disorders (D, C)
(see Box 85.2) Physiologic or Epinephrine-Induced Disorders (C)
(see Box 85.2)
Loss of Lymph Prolonged Antigenic Stimulation
• Lymphangiectasia (D, C) • Chronic infection
• Chylothorax (D, C) • Ehrlichiosis (D, C?)
• Anaplasmosis (D, C)
Impaired Lymphopoiesis • Chagas’ disease (D)
• Chemotherapy (D, C) • Babesiosis (D)
• Long-term corticosteroid use (D, C) • Leishmaniasis (D)
• Hypersensitivity reactions (?)
Viral Diseases • Immune-mediated disease (?)
• Parvoviruses (D, C) • Postvaccinal reaction (D, C)
• Feline infectious peritonitis (C)
• Feline leukemia virus (C) Leukemia
• Feline immunodeficiency virus (C) • Lymphocytic (D, C)
• Canine distemper (D) • Lymphoblastic (C, D)
• Canine infectious hepatitis (D) Hypoadrenocorticism (D)

Note: Entries in boldface are common causes; entries in italics are Note: Entries in boldface are common causes; entries in italics are
relatively common causes; entries in regular typeface are relatively common causes; entries in regular typeface are
uncommon causes. uncommon causes.
C, Cat; D, dog; ?, poorly documented. C, Cat; D, dog; ?, poorly documented.

discontinued. Contrary to popular belief, lymphopenia does Recent vaccination should be ruled out in dogs with lym-
not appear to predispose to infection. phocytosis and reactive lymphocytes in the blood smear.
In addition, I pay particular attention to the absence of Most dogs with lymphocyte counts of more than 10,000
lymphopenia in a sick dog (or cat), because it suggests that cells/µL (10 × 10 /L) have chronic ehrlichiosis, CLL, or
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there is a lymphocyte response (i.e., vector borne diseases, leishmaniasis; dogs with monocytic ehrlichiosis or anaplas-
immune mediated diseases), that the stress leukogram is mosis frequently have increased numbers of large granu-
absent due to lack of corticosteroids (Addison), or that the lar lymphocytes (LGLs), larger lymphocytes with abundant
analyzer is counting other cells as lymphocytes. cytoplasm, and large azurophilic cytoplasmic granules. LGL
lymphocytosis can also occur in dogs with CLL. Lympho-
LYMPHOCYTOSIS cyte counts of more than 20,000 cells/µL (20 × 10 /L) are
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Lymphocytosis is defined as an absolute increase in lympho- extremely rare in dogs with ehrlichiosis; that is, dogs with
cyte numbers. It is common in several clinical situations, more than 20,000 lymphocytes/µL more likely have CLL.
including fear (cats; see earlier, “Neutrophilia”), vaccination A high proportion of these dogs also has hyperprotein-
(dogs and possibly cats), chronic ehrlichiosis (dogs), ana- emia caused by a monoclonal or polyclonal gammopathy
plasmosis (dogs and cats), Addison disease (hypoadreno- (see Chapter 89). The clinical and hematologic features of
corticism, dogs), and chronic lymphocytic leukemia (CLL). monocytic ehrlichiosis and CLL are similar (e.g., cytopenia,
The lymphocytes are morphologically normal in all these hyperproteinemia, hepatosplenomegaly, lymphadenopathy).
disorders, with the exception of vaccination reactions, in Serologic tests or polymerase chain reaction (PCR) testing
which reactive lymphocytes (larger cells with a dark blue for Ehrlichia canis, immunophenotyping of peripheral blood
cytoplasm) are commonly seen. High numbers of morpho- lymphocytes, PCR assay for clonality, and bone marrow
logically abnormal (blast) lymphoid cells are found in dogs aspiration findings may be helpful in differentiating these
and cats with acute lymphoblastic leukemia (see Chapter 80). two disorders. Bone marrow cytologic findings in dogs with
In cats with marked lymphocytosis and neutrophilia, chronic ehrlichiosis usually consist of generalized hemato-
endogenous release of catecholamines should be ruled out poietic hypoplasia and plasmacytosis, whereas hypoplasia
as the cause of these hematologic abnormalities. If the cat is with increased numbers of lymphocytes is more common
fractious and blood cannot be collected without a consider- in dogs with CLL; some dogs with CLL have normal bone
able struggle, a blood sample should be collected under marrow cytologic findings. Causes of lymphocytosis in cats
chemical restraint. and dogs are listed in Box 85.7.