Page 1272 - Small Animal Internal Medicine, 6th Edition

1244 PART XI Immune-Mediated Disorders

adjunctive immunosuppressive medication concurrently.
One dose of vincristine should be considered if the throm- TABLE 73.6
VetBooks.ir bocytopenia is severe (platelet count < 15,000/µL). Whole Causes of Severe Neutropenia in Dogs and Cats
blood transfusion rather than pRBCs should be adminis-
tered in dogs with Evans syndrome that are actively bleeding.
Dogs with Evans syndrome should not be treated with ETIOLOGY EXAMPLE
heparin because of the risk of exacerbating hemorrhage due Infection Parvovirus, ehrlichiosis, bacterial
to thrombocytopenia. sepsis
Drug associated Chemotherapeutic agents, cytotoxic
Prognosis drugs, vincristine, estrogens,
The prognosis for dogs with ITP is good to guarded, with a trimethoprim/sulfadiazine,
short-term survival rate of 74% to 93%. Most dogs respond phenobarbital
to medical treatment, although relapse occurs in 9% to 58% Bone marrow Aplastic anemia, Ehrlichia canis
of dogs as drug dosages are reduced. Dogs with megakaryo- suppression infection, myelodysplasia,
cytic hypoplasia have a poor prognosis. The prognosis for myeloid hypoplasia, leukemia
dogs with concurrent IMHA and ITP is also poor, with Immune mediated Primary immune-mediated
reported mortality rates as high as 80%, although in one neutropenia
study, mortality in dogs with Evans syndrome was similar to
that of dogs with IMHA alone. See Chapter 82 for more
information on this topic. Clinical Features
In the largest retrospective report of 35 dogs with suspected
FELINE IMMUNE-MEDIATED IMN, a variety of breeds were represented and 22/35 cases
THROMBOCYTOPENIA were female. Affected dogs were typically young, with a
Most cats with thrombocytopenia have an underlying cause median age of 5 years. Clinical signs included fever, lame-
identified, and primary feline immune-mediated thrombo- ness, anorexia, and lethargy, and the duration of clinical
cytopenia is an extremely rare disorder. The clinical pre- signs ranged from 3 to 180 days. Common abnormalities
sentation and response to treatment is similar to that of detected on CBC, serum biochemistry panel, and urinalysis
dogs. Spontaneous bleeding due to thrombocytopenia is less included severe neutropenia (median 110 cells/µL), throm-
common. In the rare cases that do not respond to glucocor- bocytopenia, mild anemia, hyperglobulinemia, and increased
ticoids alone, chlorambucil is recommended as an adjunc- alkaline phosphatase activity. It has been proposed that up
tive immunosuppressant. Practitioners should be aware that to 25% of dogs diagnosed with IMN have concurrent ITP. In
platelet clumping leading to marked pseudothrombocytope- the large retrospective study, 25% of dogs had thrombocyto-
nia (i.e., <30,000/µL) is more common in cats than in dogs, penia, with 14% having platelet counts of <99,000/µL.
so a blood smear for semiquantitative platelet estimation Further evaluation of affected dogs with bacterial culture,
or a platelet count performed in citrate or heparin tubes infectious disease serology, and imaging did not reveal a
should always be evaluated in asymptomatic thrombocyto- cause for the neutropenia. Bone marrow cytology and histo-
penic cats. pathology revealed myeloid hyperplasia in two thirds of
affected dogs and myeloid hypoplasia in the other one third
of dogs, with maturation arrest identified in 20%.
IMMUNE-MEDIATED NEUTROPENIA
Diagnosis and Treatment
Etiology A clinical diagnosis of IMN is made by exclusion of other
Immune-mediated neutropenia (IMN) is rare in dogs and causes of neutropenia. Additionally, antineutrophil antibod-
cats, accounting for approximately 0.4% of cases of neu- ies can be detected by flow cytometry. Blood samples can be
tropenia (see Chapter 85). In IMN (also called idiopathic submitted to the University of Tennessee Diagnostic Immu-
neutropenia or steroid-responsive neutropenia), serum anti- nology Laboratory (UTCVM Immunology Service, 2407
neutrophil IgG antibodies can be detected by flow cytometry River Dr, Knoxville, TN 37996; immunology@utk.edu). Pre-
in the serum. Antibody and complement directed against sumptive diagnosis may be made by rapid response to treat-
myeloid cells within the bone marrow have also been identi- ment with glucocorticoids at an initial dose of 2-4 mg/kg/
fied; however, because these tests are rarely done, the term day of oral prednisone. In dogs who do not initially respond
is primarily used for dogs and cats with “idiopathic” neu- to prednisone or those who relapse during prednisone taper-
tropenia that responds to steroids. As with other immune- ing, addition of an adjunctive immunosuppressive medica-
mediated disorders, IMN may be a primary disorder or tion is appropriate. Azathioprine and cyclosporine have been
may occur secondary to drug therapy, neoplasia, or other described for the treatment of IMN. Gradual withdrawal of
immune-mediated disorder (Table 73.6). The majority of corticosteroid therapy is conducted in a similar way as
canine cases reported in the literature have been primary. described for IMHA and ITP. Some dogs require long-term
Only one case of suspected IMN in a cat has been reported. immunosuppression. Routine monitoring is important to