Page 1381 - Small Animal Internal Medicine, 6th Edition

CHAPTER 82 Anemia 1353

Dogs and cats with ACD usually do not require specific erythroid dysplasia or dyserythropoiesis induced by the
or supportive therapy because treatment of the primary virus. Dogs with PRCA occasionally have circulating sphe-
VetBooks.ir disorder causes the anemia to resolve. Although some have rocytes, indicating an immune basis for the anemia. The
direct Coombs test is also positive in more than 50% of these
advocated the use of anabolic steroids in dogs and cats with
ACD, these agents appear to be of little or no benefit. For a
therapy. Cats and dogs with bone marrow aplasia-hypoplasia
recent review of ACD I dogs and cats, please see Chikazawa dogs, and their anemia responds to immunosuppressive
and Dunning. are pancytopenic (see Chapter 86).
FeLV and FIV testing should be done in all cats with
Bone Marrow Disorders severe nonregenerative anemia, independently of their MCV.
Neoplastic, hypoplastic, or dysplastic bone marrow disorders A bone marrow aspiration or biopsy specimen should also
can result in anemia and other cytopenias. In these condi- be obtained to rule out other bone marrow disorders.
tions, a so-called crowding out of the normal erythroid pre- The FeLV envelope protein p15E suppresses erythropoi-
cursors by neoplastic or inflammatory cells (myelophthisis), esis in vitro and causes aplastic anemia in FeLV-infected cats.
paucity or absence of erythroid precursors (hypoplasia or The anemia in these cats is usually chronic and severe—a
aplasia, respectively), or maturation arrest of the erythroid PCV of 5% to 6% is relatively common—and despite sup-
precursors (dysplasia) occur. All these disorders, with the portive therapy, the condition of the patient deteriorates,
exception of PRCA (see the following section), typically affect leading the owners to request euthanasia. The supportive
more than one cell line, and the patients are bicytopenic or treatment of these cats includes whole blood or packed RBC
pancytopenic (see Chapter 86). In general, these disorders transfusions, as needed; the interval between transfusions
are chronic and the clinical signs are those of anemia (see usually shortens with each transfusion until the cat needs
p. 1340), with or without signs of the underlying disorder. transfusions weekly. Interferon administered orally may
Although some information regarding the pathogenesis of improve clinical signs, without resolution of the anemia, in
this type of anemia can be obtained by evaluating the clinical some of these cats (see Chapter 96).
and hematologic data, a definitive diagnosis is usually made FeLV-negative cats with PRCA may have a positive direct
on the basis of the cytologic or histopathologic appearance Coombs test and frequently benefit from immunosuppres-
of a bone marrow specimen and possibly by the results of sive doses of corticosteroids. I typically use 4 to 5 mg of
serologic tests or PCR assay for the infectious agent (e.g., dexamethasone/cat PO q1 to 2 weeks instead of the conven-
FeLV, FIV, Ehrlichia canis). Numerous “anemia panels” that tional prednisone or prednisolone daily or every other day.
combine serology and PCR for common infectious agents This steroid formulation is safe and effective, and I have not
in both dogs and cats are offered by reference laboratories. seen the development of secondary diabetes mellitus in the
Bone marrow (or erythroid) aplasia-hypoplasia cats treated. The use of human recombinant erythropoietin
Bone marrow aplasia-hypoplasia is characterized by (EPO; see later) does not appear to be indicated in these cats
aplasia or hypoplasia of all the bone marrow cell lines (bone because their endogenous EPO activity is higher than that of
marrow aplasia-hypoplasia or aplastic pancytopenia) or of normal cats. In addition, the long-term use of human recom-
selected cell lines, for example, erythroid precursors (RBC binant EPO may lead to the development of anti-EPO anti-
aplasia-hypoplasia or PRCA). This form of anemia (or com- bodies and resultant refractory anemia.
bined cytopenias) can be caused by a variety of agents or Bone marrow aspirates in dogs and cats with PRCA reveal
disorders (see Chapter 86). The following discussion pertains erythroid hypoplasia or hyperplasia of the early erythroid
to PRCA; some authors have referred to PRCA as the non- precursors and a maturation arrest at the rubricyte or meta-
regenerative form of immune-mediated anemia. Patholo- rubricyte stage. As noted, this poses an interesting situation
gists prefer to use PRCA for patients in which there is because most clinical pathologists use PRCA only for the
aplasia-hypoplasia of all the RBC precursors. However, dogs and cats that have erythroid hypoplasia and IHA with
because the clinical and clinicopathologic findings are iden- delayed erythroid regeneration or nonregenerative form of
tical independently of where in the RBC series the matura- immune-mediated anemia for those with erythroid hyper-
tion arrest occurs, I prefer to use PRCA. plasia and a maturation arrest. However, from a clinical
Clinically, dogs and cats with PRCA are evaluated because standpoint, both situations behave the same way and respond
of the clinical signs already discussed. Pica is common in to the same treatment, so I prefer to use PRCA for dogs and
dogs with PRCA. In contrast to ACD, in which the degree cats with either of these bone marrow cytologic findings.
of anemia and thus the severity of the clinical signs is mild, The same treatment as that used during the maintenance
cats and dogs with PRCA usually have a PCV of less than phase of IHA is recommended for affected dogs (prednisone,
15% and are usually symptomatic. Hematologically, severe 2-4 mg/kg PO q24-48h, and/or azathioprine, 50 mg/m PO
2
(normocytic normochromic) nonregenerative anemia is q24-48h). In cats, I have successfully used dexamethasone
usually the only abnormality; macrocytosis in the absence of alone (as noted earlier) or in combination with chlorambu-
reticulocytes is a consistent finding in cats with FeLV- or cil, 20 mg/m PO q2 weeks. Responses occur in approxi-
2
FIV-related aplastic anemia, and mild microcytosis can mately 70% to 80% of patients, but clinical and hematologic
occasionally be present in dogs with PRCA. The large RBC recovery may take 2 to 3 months; long-term (often lifelong)
volume in cats with retroviral infections is attributed to the treatment is usually required. Supportive treatment and