Do we need antiplatelet therapy in thrombocytosis? Pro

Aberrant Platelet Aggregation as Initial Presentation of Essential Thrombocythemia: Failure of Entero-Coated Aspirin to Reduce Platelet Hyperactivation

Essential thrombocythemia (ET) is a myeloproliferative neoplasm variant characterized by excessive production of platelets. Since the most common cause of mortality and morbidity in ET patients is thrombosis, the excessive production of platelets may cause thrombotic events. However, little is known about the function of platelets in ET. We report a female patient who presented as asymptomatic, without a remarkable medical history, and ET was diagnosed after an incidental finding of moderate thrombocytosis. Notably, together with thrombocytosis, an abnormal platelet phenotype was found for the presence of a massive, rapid and spontaneous formation of aggregates and platelet hypersensitivity to subthreshold concentrations of aggregating agonists. Bone marrow histopathological examination and genetic analysis with the JAK2 (V617F) gene mutation findings confirmed the initial suspicion of ET. Although the ET patient was placed on aspirin, the persistence of the platelet hyperactivation and hyperaggregability prompted a switch in antiplatelet medication from entero-coated (EC) to plain aspirin. As result, platelet hypersensitivity to agonists and spontaneous aggregation were no longer found. Collectively, our study demonstrates that platelet function analysis could be a reliable predictor of ET and that plain aspirin should be preferred over EC aspirin to attenuate platelet hyperreactivity.

[Role and mechanism of platelet-derived growth factor BB in thrombocytosis in Kawasaki disease]

OBJECTIVES

To study the role and mechanism of platelet-derived growth factor BB (PDGF-BB) on platelet production in Kawasaki disease (KD) mice and human megakaryocytic Dami cells through in vitro and invivo experiments.

METHODS

ELISA was used to measure the expression of PDGF in the serum of 40 children with KD and 40 healthy children. C57BL/6 mice were used to establish a model of KD and were then randomly divided into a normal group, a KD group, and an imatinib group (30 mice in each group). Routine blood test was performed for each group, and the expression of PDGF-BB, megakaryocyte colony forming unit (CFU-MK), and the megakaryocyte marker CD41 were measured. CCK-8, flow cytometry, quantitative real-time PCR, and Western blot were used to analyze the role and mechanism of PDGF-BB in platelet production in Dami cells.

RESULTS

PDGF-BB was highly expressed in the serum of KD children (P<0.001). The KD group had a higher expression level of PDGF-BB in serum (P<0.05) and significant increases in the expression of CFU-MK and CD41 (P<0.001), and the imatinib group had significant reductions in the expression of CFU-MK and CD41 (P<0.001). In vitro experiments showed that PDGF-BB promoted Dami cell proliferation, platelet production, mRNA expression of PDGFR-β, and protein expression of p-Akt (P<0.05). Compared with the PDGF-BB group, the combination group (PDGF-BB 25 ng/mL + imatinib 20 μmol/L) had significantly lower levels of platelet production, mRNA expression of PDGFR-β, and protein expression of p-Akt (P<0.05).

CONCLUSIONS

PDGF-BB may promote megakaryocyte proliferation, differentiation, and platelet production by binding to PDGFR-β and activating the PI3K/Akt pathway, and the PDGFR-β inhibitor imatinib can reduce platelet production, which provides a new strategy for the treatment of thrombocytosis in KD.

Reactive Thrombocytosis in Non-aneurysmal Subarachnoid Hemorrhage

BACKGROUND

 The role of reactive thrombocytosis in non-aneurysmal subarachnoid hemorrhage (NA-SAH) is largely unexplored to date. Therefore, the impact of a quantitative thrombocyte dynamic in patients with NA-SAH and its clinical relevance were analyzed in the present study.

METHODS

 In this retrospective analysis, 113 patients with nontraumatic and NA-SAH treated between 2003 and 2015 at our institution were included. World Federation of Neurosurgical Societies admission status, cerebral vasospasm, delayed infarction, hydrocephalus, need for ventriculoperitoneal (VP) shunt, and Fisher grade were analyzed for their association with reactive thrombocytosis.

RESULTS

 Reactive thrombocytosis was not associated with hydrocephalus (p ≥ 0.05), need for VP shunt implantation (p ≥ 0.05), cerebral vasospasm (p ≥ 0.05), or delayed cerebral ischemia (p ≥ 0.05).

CONCLUSION

 Our study is the first to investigate the role of thrombocyte dynamics, reactive thrombocytosis, and the clinical course of NA-SAH patients. Our analysis showed no significant impact of thrombocyte count on NA-SAH sequelae.

Toward the Relevance of Platelet Subpopulations for Transfusion Medicine

Circulating platelets consist of subpopulations with different age, maturation state and size. In this review, we address the association between platelet size and platelet function and summarize the current knowledge on platelet subpopulations including reticulated platelets, procoagulant platelets and platelets exposing signals to mediate their clearance. Thereby, we emphasize the impact of platelet turnover as an important condition for platelet production in vivo. Understanding of the features that characterize platelet subpopulations is very relevant for the methods of platelet concentrate production, which may enrich or deplete particular platelet subpopulations. Moreover, the concept of platelet size being associated with platelet function may be attractive for transfusion medicine as it holds the perspective to separate platelet subpopulations with specific functional capabilities.

Do we need antiplatelet therapy in thrombocytosis? Contra. Proposal for an individualized risk-adapted treatment

Thrombocytosis is a frequent laboratory finding but not a diagnosis. Therefore, elevated platelet counts (>450 x 10⁹/l) require careful diagnostic work-up to differentiate between reactive thrombocytosis (RT), caused by various conditions, and essential thrombocythemia (ET), a myeloproliferative neoplasm (MPN). In either setting, aspirin is widely used in clinical practice. However, RT (even at platelet counts >1000 x 10⁹/l) has never been shown to cause thrombosis or bleeding due to acquired von Willebrand factor defects in association with high platelet counts. Identification of reactive conditions and appropriate therapy of the underlying disorder are most relevant. By contrast to RT, ET and related MPN can be associated with thrombosis and/or hemorrhage. Current recommendations suggest the use of low-dose aspirin in all patients with ET unless contraindicated. However, the strength of this recommendation is weak, i. e. evidence level IIb grade B. A potential benefit of aspirin used for primary thromboprophylaxis in ET is mostly derived from the ECLAP study in polycythemia vera (PV). However, translating study results from PV to ET appears to be highly questionable and may be biased. In the absence of robust data regarding the benefit-risk balance of aspirin in ET, it appears reasonable (1) to stratify patients according to their individual thrombotic and bleeding risk, (2) to restrict the use of aspirin to high-risk categories and patients with microcirculatory disturbances, (3) to test for pharmacological efficacy (COX-1 inhibition; measurement of TXB₂), and (4) to modify the aspirin dosing regimen (twice instead of once daily) if required.