What is the role of platelets in Polycythemia Vera (PV)?

From the Guidelines

In Polycythemia Vera (PV), platelets play a crucial role in the increased risk of thrombotic and bleeding complications due to their elevated counts and abnormal function. The management of PV involves controlling the hematocrit level to reduce the risk of thrombotic events, with a target hematocrit level of less than 45% as established by the CYTO-PV study 1. Low-dose aspirin is also recommended to reduce the risk of thrombotic complications, as shown in the ECLAP study, which demonstrated a significant reduction in the combined risk of nonfatal myocardial infarction, nonfatal stroke, pulmonary embolism, major venous thrombosis, or death from cardiovascular causes 1. Key points to consider in the management of PV include:

• The use of cytoreductive therapies such as hydroxyurea to control platelet counts and reduce the risk of thrombotic events
• The importance of monitoring platelet counts and hematocrit levels to guide treatment decisions and assess disease progression
• The role of low-dose aspirin in reducing the risk of thrombotic complications
• The need to maintain a hematocrit level of less than 45% to reduce the risk of cardiovascular death and major thrombotic events, as established by the CYTO-PV study 1 and recommended by the European LeukemiaNet 1. Overall, the management of PV requires a comprehensive approach that takes into account the patient's individual risk factors and disease characteristics, with the goal of reducing the risk of thrombotic and bleeding complications and improving quality of life. The most recent and highest quality study, the NCCN guidelines insights: myeloproliferative neoplasms, version 2.2018 1, provides recommendations for the management of PV, including the use of hydroxyurea, interferon alfa, and peginterferon alfa as effective options for the prevention of thrombotic complications.

From the Research

Role of Platelets in Polycythemia Vera (PV)

• Platelets play a significant role in the pathogenesis of vascular occlusive events in PV, with high platelet counts associated with an increased risk of thrombotic complications 2, 3.
• The European Collaboration on Low-dose Aspirin in Polycythemia Vera prospective study found that high platelet count was associated with a lower progression rate to acute leukaemia/myelofibrosis, but had no significant relationship with thrombotic events or mortality 2.
• Platelet activation and inhibition are critical in PV, with persistently enhanced platelet activation contributing to a higher risk of both arterial and venous thrombotic complications 4.
• The use of platelet-lowering agents, such as hydroxyurea, anagrelide, and interferon alfa, is recommended to prevent thrombotic complications in 'high-risk-for-thrombosis' patients with PV 5.
• Thromboelastography (TEG) measurements have shown that PV patients demonstrate abnormal hemostasis, with a major role played by platelets rather than plasma factors, and that the hypercoagulable state in PV patients is significantly augmented following isovolemic erythrocytapheresis 3.
• Hemorheologic considerations suggest that both raised packed cell volume (PCV) values and quantitative/qualitative platelet changes play a role in the pathogenesis of vascular occlusive events in PV, with low flow rates predisposing to occlusive events 6.