Page 1263 - Small Animal Internal Medicine, 6th Edition

CHAPTER 73 Common Immune-Mediated Diseases 1235

TABLE 73.3
VetBooks.ir Secondary Causes of IMHA in Dogs and Cats DIAGNOSTIC TESTS INDICATED

EXAMPLES

Neoplasia Lymphoma Abdominal/thoracic radiographs
Hemangiosarcoma Abdominal ultrasound
Leukemia Bone marrow aspirate
Malignant histiocytosis Lymph node aspirates
Infection (see Box 73.1) Feline leukemia virus Serology
Hemotrophic mycoplasmosis IFA/PCR
Dirofilaria immitis Serology
Thoracic radiographs
Urinary tract infection
Chronic inflammation Prostatitis Urine culture
Colitis Ultrasound of urinary tract
Diskospondylitis Colonoscopy
Polyarthritis Spinal radiographs
Synovial fluid collection and radiographs
Exposure to drugs vaccines or toxins Antibiotics (sulfonamides, β-lactam Detailed history
antibiotics)
IFA, Immunofluorescent antibody; IMHA, immune-mediated hemolytic anemia; PCR, polymerase chain reaction.

Results of bone marrow evaluation in dogs with nonre- the lack of prospective studies of treatment efficacy, recom-
generative primary IMHA typically reveal erythroid hyper- mendations for approach to treatment in dogs with IMHA
plasia with a low myeloid/erythroid (M/E) ratio, although are based primarily on clinical experience rather than objec-
maturation arrest at the rubricyte or metarubricyte stage tive data.
may also be observed. Some dogs initially suspected to have When planning the management of a dog with IMHA,
IMHA on the basis of the presence of spherocytosis or a the goals of treatment should include prevention of RBC
positive Coombs test have pure red cell aplasia (PRCA). hemolysis, alleviation of tissue hypoxia by blood transfusion,
Myelofibrosis is identified on bone marrow core biopsy in prevention of thromboembolism, and provision of support-
many dogs with nonregenerative IMHA. In dogs with myelo- ive care.
fibrosis, collection of adequate bone marrow elements by
aspiration cytology is difficult. Myelofibrosis is likely a sec- PREVENTION OF HEMOLYSIS
ondary response to bone marrow injury and usually resolves Immunosuppressive drugs are the key for prevention of
in dogs that respond to treatment. hemolysis in dogs with IMHA. The mechanism of action and
In dogs without the classic morphologic changes of adverse effects associated with the use of various immuno-
immune-mediated hemolysis (regenerative anemia, autoag- suppressive drugs recommended for use in dogs and cats
glutination, spherocytes), confirming a diagnosis of IMHA with autoimmune disorders were discussed in Chapter 72.
is challenging. A positive direct Coombs test should be inter- High doses of glucocorticoids are the first line of treat-
preted cautiously in such cases because false-positive results ment for controlling hemolysis in dogs with IMHA. In dogs
may occur. The logical approach is to rule out other causes that can tolerate oral medication, prednisolone or predni-
of anemia (see Chapter 82) and use the Coombs test and sone at a dose of 2-4 mg/kg/day orally (PO) is the authors’
other indications of hemolysis as supporting evidence of corticosteroid of choice. Prednisolone may have higher bio-
IMHA if no other cause of anemia is identified. availability than prednisone in cats and possibly dogs, so it
is the best choice in both species. The higher end of the dose
Treatment range is recommended as a starting dose except in large-
Choosing an appropriate treatment regimen for dogs with breed dogs (>30 kg). Most dogs that respond to predniso-
IMHA is a frustrating task for the clinician. Lack of prospec- lone show some improvement within the first 7 days of
tive studies of treatment efficacy, the poor prognosis associ- treatment, but the full therapeutic effect may not be evident
ated with the disease, and the high cost of treatment and until 2 to 4 weeks after initiation of treatment. Indications
supportive care are some reasons for this frustration. In suggesting resolution of hemolysis include stabilization and
addition, serious complications such as pulmonary throm- then an increasing hematocrit, conversion from a positive to
boembolism and DIC are relatively common occurrences negative Coombs test, resolution of autoagglutination, reso-
but are hard to anticipate in individual patients. Because of lution of spherocytosis, normalization of the reticulocyte