Perry J.J. van Genderen

Prevention and treatment of thrombotic complications in essential thrombocythaemia : efficacy and safety of aspirin

The efficacy and safety of aspirin in the prevention and treatment of thrombosis in essential thrombocythaemia (ET) was retrospectively analysed in a cohort of 68 ET patients. 41 patients presented with thrombosis, five patients with bleeding; two patients had a paradoxical combination of bleeding and thrombosis at presentation. At presentation, patients with bleeding had significantly higher platelet and leucocyte counts than patients with thrombosis. During long‐term follow‐up the incidence of thrombosis was significantly reduced in patients receiving aspirin, either as monotherapy or in combination with cytoreduction. However, treatment with aspirin (500 mg/d) was associated with an increase in (minor) bleeding complications. In patients receiving aspirin, bleeding occurred particularly at platelet counts exceeding 1000×109/l. The overall 5‐ and 10‐years survival probability was 93% and 84% respectively, indicating that life expectancy in ET is close to normal. Although our data need confirmation in prospective clinical trials, they suggest that aspirin, particularly in lower doses (100 mg/d), may be a safe antithrombotic agent in ET with an acceptable risk for bleeding, if applied to patients with a platelet count <1000×109/l and/or absence of a bleeding history.

Coagulation disorders in young adults with acute cerebral ischaemia

Abstract We analysed the results of coagulation studies in an unselected series of young adults with acute cerebral ischaemia. Our aims were (a) to determine the prevalence of coagulation disorders among these patients, (b) to investigate the relation between the presence of coagulation abnormalities and large vessel disease or potential sources of cardiac embolism and (c) to evaluate the occurrence of thrombotic events in patients with or without coagulation disorders. One hundred and twenty consecutively admitted patients (53 men, 67 women, median age 38 years, range 15–45) who presented with acute cerebral infarction (n = 89) or a transient ischaemic attack (n = 31) were evaluated. Diagnostic studies consisted of electrocardiography, echocardiography, duplex scanning, and/or angiography. Coagulation studies included activity tests of protein S, protein C, antithrombin, plasminogen, measurement of immunoglobulin G (IgG) anticardiolipin antibodies (ACLA), and a dilute prothrombin assay. Initially, 30 patients had increased ACLA titres and 28 had an abnormal dilute prothrombin assay, suggesting lupus anticoagulant. Decreased protein S, protein C and antithrombin activity were detected in 20, 3 and 3 patients, respectively, excluding patients in whom the abnormalities could be explained by the use of medication, by pregnancy or puerperium. We detected a decreased activity of plasminogen in 5 patients. The disorders could be confirmed by a second assessment in only 2 patients with a protein S deficiency, in none of the patients with a protein C or antithrombin deficiency and in 1 patient with plasminogen deficiency. However, the abnormalities persisted in 19 of 21 patients with increased anticardiolipin IgG titres and in 9 of 20 patients with lupus anticoagulant. A confirmed coagulation disorder was not associated with stroke type or vascular risk factors, but it was more common among patients with large vessel disease (odds ratio: 3.8, 95% confidence interval (CI): 1.1–12.8). Sixteen patients had a recurrent thromboembolic event, but the risk of recurrence was not increased among patients with a confirmed coagulation disorder. Our results suggest that idiopathic coagulation disorders are found in about a quarter of young stroke patients. They are difficult to predict and probably interact with other risk factors.

Thromboxane‐dependent platelet activation in vivo precedes arterial thrombosis in thrombocythaemia: a rationale for the use of low‐dose aspirin as an antithrombotic agent

The clinical course of patients with polycythaemia vera (PV) and essential thrombocythaemia (ET) is frequently complicated by arterial thrombotic events. The pathogenesis is not clearly understood but attributed to abnormalities in platelet function. An increase in platelet thromboxane formation has been described in the majority of asymptomatic patients with thrombocythaemia, probably reflecting spontaneous platelet activation in vivo. In the present study we prospectively investigated whether an increase in platelet thromboxane formation actually precedes arterial microvascular thrombosis. In addition, we studied the effect of selective inhibition of platelet thromboxane formation on clinical outcome by reinstitution of low‐dose aspirin (50 mg/d). Six ET patients and one PV patient participated in this study. Within 10 d after withdrawal of aspirin, three patients developed arterial microvascular thrombosis of extremities (erythromelalgia), which was preceded by a 3–30‐fold increase in urinary thromboxane excretion as compared with patients who remained asymptomatic. The increased urinary thromboxane excretion and clinical signs could be inhibited by a platelet‐specific aspirin regimen of 50 mg/d without affecting vascular cyclooxygenase, indicating that platelets were the main source of the increased thromboxane generation. These data suggest that in symptomatic patients an enhanced formation of thromboxane by platelets, reflecting platelet activation in vivo, precedes the development of arterial microvascular thrombosis. These data provide a rationale for using low‐dose aspirin as an antithrombotic agent in thrombocythaemia.

Decreased half-life time of plasma von Willebrand factor collagen binding activity in essential thrombocythaemia: normalization after cytoreduction of the increased platelet count

Patients with essential thrombocythaemia (ET) exhibit a decrease of large von Willebrand factor (VWF) multimers in plasma, which is inversely related to the platelet count. In the present study we investigated whether the decrease of large VWF multimers in plasma with increasing platelet counts is the consequence of increased turnover of large VWF multimers in vivo. To that end we measured the half‐life times of endogenously released VWF:Ag and VWF:CBA (collagen binding activity) after intravenous administration of desmopressin (DDAVP) to nine ET patients and nine control subjects (N). In addition, the half‐life times of VWF:Ag and VWF:CBA were also measured in four ET patients after cytoreduction of the increased platelet count to normal or nearly normal values. Estimated half‐life times of VWF:Ag did not differ between ET patients and normals (11.0 ± 4.0 h v 12.4 ± 2.5 h, P  > 0.05). Estimated half‐life times of VWF:CBA were significantly lower in ET patients as compared with normal individuals (6.1 ± 2.0 h v 8.4 ± 2.5 h, P  < 0.05). After cytoreduction of the increased platelet count to (nearly) normal values in all four ET patients the half‐life time of VWF:CBA significantly (P = 0.014) increased from 5.2 ± 1.2 h to 8.7 ± 2.0 h. Our data suggest that platelets may play a role in the homeostasis of circulating von Willebrand factor, which may compromise normal haemostasis at fairly increased platelet counts.

Interference with the Host Haemostatic System by Schistosomes

Schistosomes, parasitic flatworms that cause the tropical disease schistosomiasis, are still a threat. They are responsible for 200 million infections worldwide and an estimated 280,000 deaths annually in sub-Saharan Africa alone. The adult parasites reside as pairs in the mesenteric or perivesicular veins of their human host, where they can survive for up to 30 years. The parasite is a potential activator of blood coagulation according to Virchows triad, because it is expected to alter blood flow and endothelial function, leading to hypercoagulability. In contrast, hepatosplenic schistosomiasis patients are in a hypocoagulable and hyperfibrinolytic state, indicating that schistosomes interfere with the haemostatic system of their host. In this review, the interactions of schistosomes with primary haemostasis, secondary haemostasis, fibrinolysis, and the vascular tone will be discussed to provide insight into the reduction in coagulation observed in schistosomiasis patients. Interference with the haemostatic system by pathogens is a common mechanism and has been described for other parasitic worms, bacteria, and fungi as a mechanism to support survival and spread or enhance virulence. Insight into the mechanisms used by schistosomes to interfere with the haemostatic system will provide important insight into the maintenance of the parasitic life cycle within the host. This knowledge may reveal new potential anti-schistosome drug and vaccine targets. In addition, some of the survival mechanisms employed by schistosomes might be used by other pathogens, and therefore, these mechanisms that interfere with host haemostasis might be a broad target for drug development against blood-dwelling pathogens. Also, schistosome antithrombotic or thrombolytic molecules could form potential new drugs in the treatment of haemostatic disorders.

Salmonella Subtypes with Increased MICs for Azithromycin in Travelers Returned to the Netherlands

Antimicrobial susceptibility was analyzed for 354 typhoidal Salmonella isolates collected during 1999–2012 in the Netherlands. In 16.1% of all isolates and in 23.8% of all isolates that showed increased MICs for ciprofloxacin, the MIC for azithromycin was increased. This resistance may complicate empirical treatment of enteric fever.

Atypical Transient Ischemic Attacks in Thrombocythemia of Various Myeloproliferative Disorders

Neurological symptoms of transient unsteadiness, dysarthria, dysphasia, dysbasia, transient monoor hemiparesis, hemiparesis, scintillating scotomas, amaurosis fugax, vertigo, dizziness, migraine accompaniments, syncope and seizures were the presenting manifestations of thrombocythemia in various myeloproliferative disorders. Erythromelalgia preceded or followed the neurologic ischemic attacks. The neurologic and ocular attacks usually had a sudden onset, lasted for a few seconds to several minutes and occurred independently or sequentially rather than simultaneously. This clinical syndrome is caused by platelet-mediated ischemic and thrombotic processes in the end-arterial microvasculature and reflects the existence of a platelet dependent and aspirin responsive arterial thrombophilia in thrombocythemia as novel disease entity, which confirms and elucidates Mitchells hypothesis.

3 Acquired von Willebrand disease

Acquired von Willebrand disease (AvWD) is an acquired bleeding disorder which may suddenly become manifest in individuals, usually in the absence of a personal or family history of bleedings and frequently in association with monoclonal gammopathies, lymphoproliferative, myeloproliferative and autoimmune disorders. In a minority of the cases AvWD may develop in association with drugs or solid tumours. Pathogenetic mechanisms involve autoantibodies directed against von Willebrand factor (vWF) resulting in a rapid clearance of vWF from the circulation and/or inactivation of plasma vWF; absorption or adsorption of plasma vWF to malignant cells; drug-induced or cell-mediated proteolysis of plasma vWF; acquired decrease in synthesis of vWF and/or release of vWF from storage sites; or precipitation of plasma vWF. Treatment options include—whenever possible—treatment of the underlying disorder or symptomatic treatment aimed at replacing the loss of vWF by either infusion of vWF-rich concentrates or administration of desmopressin (DDAVP). In selected cases with anti-vWF antibodies, administration of high-dose intravenous gammaglobulin, plasma exchange or extracorporeal immunoadsorption may be successful.

Acquired von Willebrand Disease in Myeloproliferative Disorders

The laboratory features of acquired von Willebrand defect (AvWD) in myeloproliferative disorders (MPD) are characterized by a very high platelet count, a normal or prolonged bleeding time, a normal factor VIII and von Willebrand factor (vWF) antigen level, but a decreased vWF-ristocetine cofactor activity and collagen binding activity with a decrease or absence of large vWF-multimers simulating a type II von Willebrand factor deficiency. Although the pathogenesis of type II AvWD in MPD remains unclear, evidence is accumulating that the increased number of platelets in the circulating blood seems to be directly responsible for the observed decrease of large vWF-multimers in plasma leading to a spontaneous bleeding tendency at very high platelet counts. This observation may have clinical implications for the use of platelet anti-aggregants such as aspirin in MPD at platelet counts in excess of 1000 to 2000 x 10(9)/L.

Effectiveness of High‐Dose Intravenous Gamma Globulin Therapy in Acquired von Willebrand's Disease

An 82‐year‐old patient with acquired von Willebrands disease in association with a non‐Hodgkin lymphoma and a benign IgGλ monoclonal paraproteinaemia is described with severe recurring nasopharyngeal bleedings, who responded poorly to desmopressin (DDAVP) and factor VIII/von Willebrand factor concentrates but was successfully treated with high‐dose intravenous γ‐globulin therapy.