Functional compensation of the low platelet count by increased individual platelet size in a patient with May-Hegglin anomaly presenting with acute myocardial infarction

Why thromboembolism occurs in some patients with thrombocytopenia and treatment strategies

Platelets play such an important role in the process of thrombosis that patients with thrombocytopenia generally have an increased risk of bleeding. However, abnormal thrombotic events can sometimes occur in patients with thrombocytopenia, which is unusual and inexplicable. The treatments for thrombocytopenia and thromboembolism are usually contradictory. This review introduces the mechanisms of thromboembolism in patients with different types of thrombocytopenia and outlines treatment recommendations for the prevention and treatment of thrombosis. According to the cause of thrombocytopenia, this article addresses four etiologies, including inherited thrombocytopenia (Myh9-related disease, ANKRD26-associated thrombocytopenia, Glanzmann thrombasthenia, Bernard-Soulier syndrome), thrombotic microangiopathy (thrombotic thrombocytopenic purpura, atypical hemolytic uremic syndrome, hemolytic uremic syndrome, Hemolysis Elevated Liver enzymes and Low Platelets syndrome, disseminated intravascular coagulation), autoimmune-related thrombocytopenia (immune thrombocytopenic purpura, antiphospholipid syndrome, systemic lupus erythematosus), and acquired thrombocytopenia (Infection-induced thrombocytopenia and drug-induced thrombocytopenia, heparin-induced thrombocytopenia). We hope to provide more evidence for clinical applications and future research.

Thrombin generation in two families with MYH9-related platelet disorder

MYH9-related platelet disorders are inherited macrothrombocytopenias with additional clinical manifestations including renal failure, hearing loss, pre-senile cataract, and inclusion bodies in leucocytes that are present in different combinations. The MYH9 gene codes for the cytoplasmic contractile protein non-muscular myosin heavy chain IIA, present in several tissues. The bleeding tendency is usually mild to moderate but rarely, thrombotic complications are also seen. We report on the thrombin generation potential (ETP) in patients with MYH9-related disease with and without arterial thrombosis. In family A, four affected members [c.5521G>A mutation causing p.(Glu1841Lys)] were evaluated. Three of them had a moderate bleeding tendency and in two renal insufficiency and hearing loss were already present. These two patients had an arterial thrombosis (myocardial infarction and pons infarction, respectively) before 50 years of age. In family B, two members were affected [c.4679T>G, resulting in p.(Val1560Gly)]. Their bleeding tendency was mild (bleeding scores 4 and 3, respectively). Thrombelastography (ROTEM) was normal in all six individuals. ETP was below the normal range in family B. However, in family A, the two members affected by thrombosis had a normal ETP, indicating that other factors compensated for the low platelet count and might have contributed to the arterial thrombosis.

Myocardial Infarctions and Other Acute Coronary Syndromes in Rare Congenital Bleeding Disorders

Objective:

To investigate the occurrence of myocardial infarction or other acute coronary syndromes in rare congenital bleeding disorders.

Patients:

All patients with factor I (FI), factor II (FII), factor V (FV), factor VII (FVII), factor X (FX), factor XI (FXI), or factor XIII (FXIII) deficiency or abnormality reported to have presented a myocardial infarction or another acute coronary syndrome were investigated. The condition had to be demonstrated by objective means, including a coronary/angiography. Cases of stable angina were excluded.

Results:

A total of 53 patients (4 had FI, 2 had FV, 2 had FVII, 36 had FXI, 1 had FXIII deficiency, and 8 patients had platelet disorders) met the inclusion criteria . No patient with FII or FX deficiency and acute coronary disease met the inclusion criteria. In the majority of patients, common risk factors were present, namely hypertension, hypercholesterolemia, smoking, and diabetes. Replacement therapy was involved in 5 cases.

Conclusion:

The congenital hypocoagulability present in these patients was unable to allow a protection from acute coronary diseases. The significance of the findings is discussed.

Occurrence of thrombosis in congenital thrombocytopenic disorders: a critical annotation of the literature

Patients with a low platelet count are prone to bleeding. The occurrence of a thrombotic event in congenital thrombocytopenic patients is rare and puzzling. At least nine patients with Glanzmann thrombasthenia have been reported to have had a thrombotic event, eight venous and one arterial (intracardiac, in the left ventricle). On the contrary, three patients with Bernard-Soulier syndrome have been shown to have had arterial thrombosis (myocardial infarction) but no venous thrombosis. Finally, seven patients with the familiar macrothrombocytopenia due to alterations of the MYH9 gene have been reported to have had thrombosis (five myocardial infractions, one ischemic stroke, one deep vein thrombosis and one portal vein thrombosis). The significance of these findings is discussed with particular emphasis on the discrepancy between venous and arterial thrombosis seen in patients with Glanzmann thrombasthenia and Bernard-Soulier syndrome.

Romiplostim administration shows reduced megakaryocyte response-capacity and increased myelofibrosis in a mouse model of MYH9-RD

Macrothrombocytopenia in MYH9-related disease (MYH9-RD) results from defects in nonmuscular myosin-IIA function. Thrombopoietin receptor agonists (eltrombopag; romiplostim) seem to improve hemostasis, but little is known about their biologic effects in MYH9-RD. We administered romiplostim to Myh9−/− mice (100 μg/kg, every 3 days, during 1 month). MKs increased to similar numbers in Myh9−/− and wild-type (WT) mice (with an increase in immature MKs), but Myh9−/− platelet count response was much less (2.5-fold vs 8-fold increase). A strong increase in MK nuclei emboli in the lung, in WT and Myh9−/− mice, indicates increased transmigration of MKs from the BM. Prolonged (but not acute) treatment with romiplostim decreased expression of GPIb-IX-V complex and GPVI, but not of GPIIbIIIa, and bleeding time increased in WT mice. Microcirculation was not altered by the increased number of large platelets in any of the assessed organs, but in Myh9−/− mice a much stronger increase in BM reticulin fibers was present after 4 weeks of romiplostim treatment vs WT mice. These data further encourage short-term use of thrombopoietic agents in patients with MYH9-RDs; however, myelofibrosis has to be considered as a potential severe adverse effect during longer treatment. Reduction of GPIbIX/GPVI expression by romiplostim requires further studies.

Cerebral infarction in a patient with macrothrombocytopenia with leukocyte inclusions (MTCP, May-Hegglin anomaly/Sebastian syndrome)

We report on a 78-year-old woman patient with macrothrombocytopenia with leukocyte inclusions (MTCP, May-Hegglin anomaly/Sebastian syndrome), who had no history of hemorrhagic symptoms and had a platelet count of 10,000 or less, but had a cerebral infarction. The patient was found to have idiopathic thrombocytopenic purpura, hypertension, and atrial fibrillation 16 years ago, yet received no medication. She was found to have had a cerebral infarction with aphasia as the chief complaint and was admitted to our hospital. Thrombocytopenia was found in three family members. Blood examinations revealed normal bleeding time and platelet aggregation ability. The patient was found to have the triad of giant platelets, thrombocytopenia, and inclusion bodies in leukocytes. Genetic analysis showed a mutation of the MYH-9 gene in the patients second daughter. Consequently, this patient received a diagnosis of MTCP. There have only been a few reports of the onset of thrombosis in patients with MTCP and no reports of the onset of cerebral infarction. Our report is the first case of MTCP in a patient with cerebral infarction.

Platelet-VWF complexes are preferred substrates of ADAMTS13 under fluid shear stress

Endothelial cells secrete prothrombotic ultralarge von Willebrand factor (VWF) multimers, and the metalloprotease ADAMTS13 cleaves them into smaller, less dangerous multimers. This reaction is stimulated by tensile force applied to the VWF substrate, which may occur on cell surfaces or in the circulating blood. The cleavage of soluble VWF by ADAMTS13 was accelerated dramatically by a combination of platelets and fluid shear stress applied in a cone-plate viscometer. Platelet-dependent cleavage of VWF was blocked by an anti-GPIbalpha monoclonal antibody or by a recombinant soluble fragment of GPIbalpha that prevents platelet-VWF binding. Multimeric gel analysis showed that shear and platelet-dependent cleavage consumed large VWF multimers. Therefore, ADAMTS13 preferentially acts on platelet-VWF complexes under fluid shear stress. This reaction is likely to account for a majority of VWF proteolysis after secretion and to determine the steady-state size distribution of circulating VWF multimers in vivo.

Inherited giant platelet disorders. Classification and literature review

Inherited giant platelet disorders are extremely rare. The aim of this article is to review the clinical and laboratory features of this heterogeneous group and to arrive at a working classification. We conducted our literature search using the National Library of Medicine database. A total of 12 clinical entities were described. We classified them into 4 groups depending on the clinical and structural abnormalities. The pathophysiology of these disorders is largely unknown, and more research is needed, particularly in the light of recent advances in laboratory medicine. This review may provide a valuable reference for clinicians and may form a basis for future classification and research.