Essential thrombocythemia in a cat.

The diagnosis of essential thrombocythemia in a cat was made by fulfilling the five applicable criteria set forth by the Polycythemia Vera Study Group for use in humans. The criteria were 1) a platelet count persistently above 600,000/microL, 2) a normal initial hematocrit that did not rise in response to iron therapy, 3) normal serum iron concentration, 4) absence of collagen fibrosis of the bone marrow, and 5) no cause for reactive thrombocytosis. In addition, normal thrombopoietin concentrations and splenic hypofunction were demonstrated. Melphalan was not effective in decreasing the platelet count and the cat died of sepsis.