Polycythemia vera in a cat and management with hydroxyurea

Abstract

Polycythemia vera (PV) was diagnosed in a four-year-old domestic shorthair evaluated for hind-limb ataxia, extension of all claws, and difficulty in jumping to elevated surfaces. Mild cardiac hypertrophy also was diagnosed. Initial laboratory evaluation revealed polycythemia (packed cell volume [PCV], 75%) and normal serum total protein (7.5 g/dl). Definitive diagnosis of PV was reached by excluding causes of relative and secondary absolute polycythemia using radiography, ultrasonography, and blood gases, and by measuring serum erythropoietin concentration by radioimmunoassay (13 mU/ml) and an enzyme-linked immunosorbent assay (ELISA) method (8.0 mU/ml). Bone-marrow biopsy revealed relative erythroid hyperplasia characteristic of myeloproliferative disease. Clinical signs were controlled with hydroxyurea (12.2 mg/kg body weight) and occasional phlebotomy. Polycythemia vera is an uncommon feline disease, and clinical reports on the use of hydroxyurea to manage the condition in the cat are lacking.

Hydroxyurea for Treatment of Polycythemia Secondary to Right-to-Left Shunting Patent Ductus Arteriosus in 4 Dogs

“…5,6 Most clinical reports cite cytopenias as the most frequent cause of dosage change or discontinuation of this drug when used to treat myeloproliferative disorders in dogs and cats. 10,22,25 In 1 report, reversible alopecia was reported as an adverse effect of chronic hydroxyurea therapy in a dog with chronic granulocytic leukemia at a dosage rate similar to that used in the present study (50 mg/kg administered 2 days out of 3). 23 Two of the dogs in this series had mild alopecia noted; the hair regrew without adjustments to medication.…”

“…Hydroxyurea is an antineoplastic agent that causes reversible bone marrow suppression by inhibiting DNA synthesis, and has been recommended for treatment of polycythemia and other blood dyscrasias in dogs, cats, and humans. 5,6,[20][21][22][23][24] Potential advantages of hydroxyurea over phlebotomy in polycythemic dogs with rPDA include avoidance of clinical adverse effects of phlebotomy, such as weakness, and decreased risk of thrombosis. In addition, use of hydroxyurea to control PCV avoids the development of iron deficiency, which, when accompanied by hypochromia and microcytosis, may increase blood viscosity.…”

“…The most effective dose regimen for chronic control of polycythemia in dogs is unknown. Multiple hydroxyurea dosage regimens have been suggested in the veterinary literature, but occur either as case reports of chemotherapy of polycythemia vera 6,22 or other myeloproliferative diseases 5,28,29 or as general recommendations regarding chemotherapy of myeloproliferative disease. 18,27 No primary reports of hydroxyurea treatment regimens for polycythemia secondary to cyanotic heart disease could be located.…”

The kinetics of clonal dominance in myeloproliferative disorders

“…In virtual cats, clonal dominance took 7.0 Ϯ 1.2 years, a time course of disease progression consistent with observations in clinical veterinary practice. [28][29][30] That clonal dominance in mice required 2 to 3 years, longer than a mouse's lifetime, may explain the absence of experimental murine models in which myeloproliferative disorders develop from a single transformed cell.…”

Case Report on Feline Polycythemia Vera

“…Polycythemia vera is relatively uncommon in small animal practice [1], but should still be considered in cases of neurologic disorders, especially with the presence of bright red ears, paws, or gums [2]. Due to the vascular effects of the disease such as decreased oxygen transport and obstructed blood flow, atypical cases may present first with secondary symptoms such as uveitis [3].…”