Case-based approach to anemia (Proceedings) - Veterinary Healthcare
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Case-based approach to anemia (Proceedings)


CVC IN KANSAS CITY PROCEEDINGS


Generalized Bone Marrow Hypoplasia

Generalized bone marrow hypoplasia may result from radiation, toxic, or infectious insults to the bone marrow. Common toxins include estrogen, chloramphenicol, phenylbutazone, antifungals, and chemotherapeutic drugs. Infectious diseases resulting in bone marrow hypoplasia include feline leukemia and chronic Ehrlichiosis. Generalized bone marrow hypoplasia may also result from the crowding out of normal bone marrow precursors by neoplastic cells, a process termed myelopthisis. The most common neoplastic causes are the hematopoietic and lymphoid neoplasms including lymphosarcoma, granulocytic leukemia, and lymphoid leukemias. Myelofibrosis, the replacement of marrow spaces by connective/scar tissue, usually represents the endpoint of previous severe marrow injury (as in the case of estrogen toxicity and ionizing radiation) or it may occur spontaneously. Peripheral blood features of myelofibrosis usually include severe nonregenerative anemia, severe leukopenia, and a variable platelet response. Confirmation of the diagnosis depends on marrow core biopsy with a demonstration of connective tissue filling the marrow space.

Normal to Hypercellular Bone Marrow

Iron deficiency anemia results from chronic blood loss. In young animals, parasitic infection is the primary ruleout for iron deficiency anemia, while in older animals, gastrointestinal masses or ulcers are generally implicated. Chronic blood loss leads to depletion of bone marrow iron stores over time, resulting in inability to form hemoglobin. Nuclear maturation of RBC precursors is normal however. Precursors continue to divide, getting smaller in size because they never acquire a complete amount of hemoglobin. This results in a hypercellular bone marrow with a build up of metarubricytes. Diagnosis is based on the presence of microcytic, hypochromic anemia, thrombocytosis, source of blood loss, and a bone marrow smear containing no stainable iron. Low serum iron is not diagnostic as it may rapidly decrease with inflammatory disease as a result of tissue sequestration. Treatment is aimed at removal of the source of blood loss. Ferrous sulfate may be administered at a dose of 100-300 mg per day in dogs and 50-100 mg per day in cats if needed. Note that this dose refers to ferrous sulfate, not elemental iron. Reticulocytosis should develop within 3-4 days of supplementation.

Myelodysplasia refers to a poorly understood group of diseases characterized by non-regenerative anemia or pancytopenia and prominent dysplastic changes in the bone marrow. Abnormal erythrocytes are generally unable to completely differentiate and early cell death results. Myelodysplasia may result from idiopathic (primary), neoplastic, toxic, immune-mediated, or infectious (FeLV) causes. The myelodysplasias tend to carry a very guarded prognosis, with treatment aimed at immunosuppression, chemotherapy, and/or erythropoietin depending on the suspected cause.

General Comments on the Treatment of Non-Regenerative Anemias

Treatment of decreased production anemia is best aimed at identifying and eliminating any underlying disease processes or myelosuppressive drugs. Once this is done, clinical experience suggests that the most important thing we can do for patient is to buy time for the bone marrow to repopulate with normal precursor cells. Blood transfusions should be provided as needed until the patient is able to mount a regenerative response of their own. Most patients with non-regenerative anemia require transfusions every 4-6 weeks until their disease is well controlled. Broad-spectrum antibiotics are indicated in the event of severe neutropenia to prevent secondary infections. Immunosuppressive agents may be indicated if an immune-mediated disease (eg. red cell aplasia) is identified or strongly suspected. Myeloproliferative diseases and myelodysplasia tend to carry a poor prognosis, but other forms of decreased production anemia may respond well if the underlying disease or insult is eliminated and adequate time is provided for recovery.

Conclusion

A variety of diseases, both immunologic and non-immunologic in nature, may result in anemia and/or hemolysis in veterinary patients. Successful management relies upon accurate diagnosis and treatment of the underlying disease process. Simple test to help classify a patient's anemia as blood loss, hemolysis, or decreased production may facilitate correct diagnosis. Initiation of immunosuppressive therapy prior to performing a methodical search for infectious, neoplastic, or other causes of anemia may result in therapeutic "missteps" and treatment failure.

References

McManus PM, Craig LE. Correlation between leukocytosis and necropsy findings in dogs with immune-mediated hemolytic anemia: 34 cases (1994-1999). J Am Vet Med Assoc 2001;218:1308-1313.

Duval D, Giger U. Vaccine-associated immune-mediated hemolytic anemia in the dog. J Vet Intern Med 1996;10:290-295.

Stegman JR, Birkenheuer AJ, Kruger JM, et al. Transfusion-associated Babesia gibsoni infection in a dog. J Am Vet Med Assoc 2003;222:959-963.

Birkenheuer AJ, Levy MG, Breitschwerdt EB. Efficacy of combined atovaquone and azithromycin for therapy of chronic Babesia gibsoni infections in dogs. J Vet Intern Med 2004;18:494-498.

Van Audenhove A, Verhoef G, Peetermans WE, et al. Autoimmune haemolytic anaemia triggered by Bartonella henselae infection: a case report. Br J Haematology 2001;115:924-925.

Stokol T, Blue JT. Pure red cell aplasia in cats: 9 cases (1989-1997). J Am Vet Med Assoc 1999;214:75-79.

Stokol T, Blue JT, French TW. Idiopathic pure red cell aplasia and nonregenerative immune-mediated anemia in dogs: 43 cases (1988-1999). J Am Vet Med Assoc 2000;216:1429-1436.

Weiss DJ. Primary pure red cell aplasia in dogs: 13 cases (1996-2000). J Am Vet Med Assoc 2002;221:93-95.


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