Overview

• A disorder of hematopoietic precursor cells characterized by replacement of normal bone marrow with adipose tissue. There is decreased production of granulocytes, erythrocytes, and platelets, resulting in pancytopenia in the peripheral blood. The disease is sometimes also referred to as aplastic pancytopenia.
• In the acute form, neutropenia and thrombocytopenia predominate because of the shorter life spans of these cells; in the chronic form, nonregenerative anemia also occurs. In both forms, the bone marrow exhibits variable degrees of panhypoplasia.
• There are many precipitating causes of deficient hematopoiesis, including infectious diseases, drug administration, starvation and toxin exposure; immune-mediated mechanisms are often suspected.
• Hemic/lymphatic/immune systems affected.

Signalment

Dogs and cats, no apparent breed or sex predilection. In one study, the mean age of nine affected dogs was 3 years.

Signs

• Acute form: fever, petechial hemorrhages, epistaxis, hematuria, melena; i.e., signs due to neutropenia and thrombocytopenia.
• Chronic form: pale mucous membranes, weakness, lethargy; i.e., signs due to anemia, in addition to signs observed in acute forms.

Causes & Risk Factors

Often not identified

Differential Diagnosis

Causes of pancytopenia with normal to increased bone marrow cellularity (e.g., myelodysplastic disorders, leukemia, myelofibrosis).

CBC/Biochemistry/Urinalysis

• Leukopenia characterized by neutropenia with or without lymphopenia.
• Normocytic, normochromic, nonregenerative anemia.
• Thrombocytopenia.

Other Laboratory Tests

• Immunologic tests for infectious diseases (e.g., serologic titers, ELISA, IFA).
• PCR for infectious agents.
• Serologic test for antierythrocyte antibodies (Coombs' test).

Imaging

N/A

Diagnostic Procedures

• Bone marrow aspiration-frequently an inadequate or fatty sample is obtained because of decreased hematopoietic tissue and replacement by adipocytes.
• Bone marrow core biopsy-permits an evaluation of architecture and reveals hypoplasia of cell lines and replacement by adipose tissue.

Drug(s) Of Choice

• Cyclosporine A-10–25 mg/kg PO q12h (dogs), 4–5 mg/kg PO q12h (cats).
• Recombinant hematopoietic growth factors (e.g., rhG-CSF: 5 µg/kg/day SC).
• Androgen and corticosteroid administration have been largely unsuccessful.

Contraindications/Possible Interactions

N/A

Other Drugs

• Antibiotics to treat secondary infections if fever and neutropenia present.
• Whole or component blood transfusion if indicated.

Patient Monitoring

• Daily physical examination.
• CBC every 3–5 days to weekly.
• Repeat bone marrow evaluation if necessary.

Prevention/Avoidance

• Castration of cryptorchid males.
• Vaccination for infectious diseases.
• Frequent monitoring of CBC in cancer patients receiving chemotherapy or radiation.

Possible Complications

• Sepsis
• Hemorrhage

Expected Course and Prognosis

• Guarded to poor.
• Recovery of hematopoiesis may take weeks to months, if it occurs at all.
• Spontaneous recovery occasionally occurs, especially in younger animals.

See Also

Pancytopenia

Abbreviations

• ELISA = enzyme-linked immunosorbent assay
• FeLV = feline leukemia virus
• FIV = feline immunodeficiency virus
• IFA = immunofluorescent antibody (test)
• NSAID = nonsteroidal anti-inflammatory drug
• PCR = polymerase chain reaction
• rhG-CSF = recombinant human granulocyte colony-stimulating factor

Author R. Darren Wood

Consulting Editor Alan H. Rebar