PV is a myeloproliferative disorder resulting in an elevated absolute red blood cell mass because of uncontrolled red blood cell production. This is typically associated with an increase in WBC and PLT production. The increase in WBCs and PLTs is secondary to an abnormal clone of hematopoietic stem cells with increased sensitivity to different maturation growth factors. PV is overall rare, occurring in 0.6-1.6 persons per million population. The peak incidence of PV is 50–70 years of age. However, PV may occur in persons of all age groups, including young adults and children, albeit rarely .
The increased hematocrit of PV is the main determinant of blood viscosity. As the viscosity increases, cerebral blood flow decreases [6, 7]. PLT marginalization with increased contact to vessel walls occurs, along with local effect of a high hematocrit on vessel walls [6, 7]. This fulfils all three components of Virchow’s triad , and is consistent with the thought that many strokes in polycythemic patients are due to propagation of a local thrombus [6, 7, 13, 14].
Other mechanisms have been proposed. A 1960 case series from the Mayo Clinic that reviewed PV patients with neurological symptoms discussed the possibility of embolic etiology, but dismissed it because of lack of clinical evidence for a source . This was in the pre-CT, MRI and Doppler era, however, and its conclusions may now be premature in light of present-day neuroimaging. Four prior case reports in adults have documented scattered lesions in an embolic pattern without evidence of patent foramen ovale, cardiac vegetations, or plaque rupture [15–17]. In two of these cases, transesophageal echocardiography demonstrated left atrial “microthrombi” [15, 16]. While these were not seen in our case report, the echocardiogram was not obtained until after hemodilution had occurred, which may have resolved the tendency to form thrombi. Furthermore, any cardiac clot may not have been seen since it probably had already embolized prior to our investigations. We therefore postulate that the patient’s PV predisposed him to a prothrombotic state which resulted in an unseen cardiac thrombus which in turn embolized to the cerebrum.
Management of acute ischemic stroke in polycythemia is also unique; it is the only situation where the American Heart Association stroke guidelines suggest a possible value of hemodilution . Additionally, although a meta-analysis of publications did not show a convincing benefit of hemodilution in clinical outcomes of stroke patients in general, the conclusion was that it might be beneficial in polycythemic patients with acute ischemic stroke. If the etiology is the formation of microemboli in the atria due to hyperviscosity, then hemodilution with venisection is likely the most expedient and safest acute treatment.
We feel that there are unique aspects of this case. Firstly, it is example of an acute ischemic stroke due to PV which responded to hemodilution, of which there are few published case reports to date in the literature. Also, it is unusual for PV to present with acute embolic ischemia, as most previously published cases suggest local vessel wall thrombus propagation. We hope that this case reports serves as a reminder of the association of cerebral ischemia and PV.