Hydroxycarbamide associated platelet count oscillations in a patient with polycythaemia vera. A case report and review of the literature.

We describe an unusual case of oscillating platelet counts in a patient with polycythaemia vera. Following commencement of cytoreductive hydroxycarbamide therapy, episodes of thrombocytopenia were followed regularly by thrombocytosis. Platelet counts fluctuated periodically between approximately 200 and 800 x 109/l, with a 28 day cycle duration. Frequent adjustment of the hydroxycarbamide dose was not successful in preventing the oscillations in platelet count. In contrast, maintenance of a constant dose led to a gradual damping of the cycles and thus termination of the large oscillations. The case further implicates hydroxycarbamide as a potential cause of cyclic variations in platelet counts, and demonstrates that cessation of this drug is not always necessary in order to treat this phenomenon.