Platelet function abnormalities in the myeloproliferative disorders

Platelet-rich plasma serotonin levels in chronic myeloproliferative disorders: evaluation of diagnostic use and comparison with the neutrophil PRV-1 assay

In a prospective study of 109 subjects, an enzyme-linked immunosorbent assay (ELISA) was used to measure platelet-rich plasma (PRP) serotonin levels in patients with polycythaemia vera (PV; n = 27), essential thrombocythaemia (ET; n = 14), myelofibrosis with myeloid metaplasia (MMM; n = 30), secondary or spurious polycythaemia (SP; n = 22) and controls (n = 16). Nine study subjects who were taking a selective serotonin reuptake inhibitor (SSRI) all displayed a markedly decreased PRP serotonin level (median, 24.2 ng/10(9) platelets; range, 0-49.3) and were therefore excluded from further analysis. Among the remaining 100 subjects, the median and range of PRP serotonin levels, in ng/10(9) platelets, was significantly lower in MMM (89.5; 0-278.3), PV (204.8; 0-496.0) and ET (385.3; 136.8-1025.7) compared with both SP (608.8; 369.0-1780.1) and controls (567.2; 359.9-1071.1). Neutrophil polycythaemia rubra vera-1 (PRV-1) expression was concurrently assayed by real-time polymerase chain reaction in 69 patients (23 PV, 17 SP, 12 ET, seven MMM, 10 controls). PRP serotonin measurement performed as well as the PRV-1 assay in distinguishing PV from SP (93% vs. 86% test accuracy). The current study suggests that PRP serotonin concentration might be considered as one of the several biological markers that complement each other for the diagnosis of PV.

Platelet activation via the collagen receptor GPVI is not altered in platelets from chronic myeloid leukaemia patients despite the presence of the constitutively phosphorylated adapter protein CrkL

In this study, we show that the adapter proteins CrkL and Cbl undergo increases in tyrosine phosphorylation and form an intracellular complex in platelets stimulated with the snake venom toxin convulxin, a selective agonist at the collagen receptor glycoprotein VI (GPVI). Constitutive tyrosine phosphorylation of CrkL has previously been reported in platelets from chronic myeloid leukaemia (CML) patients. This was confirmed in the present study, and shown to result in a weak constitutive association of CrkL with Cbl and a number of other unidentified tyrosine-phosphorylated proteins. There was no further increase in phosphorylation of CrkL in CML platelets in response to GPVI activation, whereas phosphorylation of Cbl and its association with CrkL were potentiated. In addition, this was accompanied by a small increase in p42/ 44 mapkinase (MAPK) activity in CML platelets. The functional consequence of the presence of constitutively phosphorylated proteins in CML platelets was investigated by measurement of aminophospholipid exposure and alpha-granule secretion. This revealed little alteration in the concentration-response curves for either in CML platelets stimulated via GPVI, although maximal levels of P-selectin were depressed. Despite the minimal effect on platelet activation in CML patients, we cannot exclude a role for CrkL or Cbl in signal transduction pathways stimulated via GPVI.

Thrombosis and bleeding in myeloproliferative disorders: identification of at-risk patients with whole blood platelet aggregation studies

Seventy-five patients with chronic myeloproliferative disorders were studied to investigate platelet function by simultaneous measurement of platelet aggregation by the impedance method and ATP dense granule release using a whole blood platelet lumi-aggregometer, in an attempt to identify patients at risk for thrombosis and bleeding. Thirty-nine patients had at least one abnormal result indicating platelet hyperactivity (i.e. impedance or release with one agonist being above the reference range); 16 patients had platelet hypoactivity (i.e. at least one result was below the reference range), whilst 14 had co-existence of hyper- and hypoactivity. Six patients had normal results. 20/53 patients with platelet hyperactivity (alone or mixed) had a positive history of venous and/or arterial thrombosis; in comparison, only two of the other 22 patients had a positive history. During a median follow-up of 33 months, nine patients with and one patient without platelet hyperactivity respectively developed new thrombotic events before the addition of specific therapy. A total of 50 patients with and eight patients without platelet hyperactivity respectively received specific treatment including aspirin and/or cytotoxic therapy. All but one elderly patient with platelet hyperactivity have remained free of new thrombotic events on specific therapy. Two of the 17 patients with platelet hypoactivity had major clinical bleeding. These observations highlight the need to test platelets for hyper- as well as hypo-function and suggest a useful role for routine whole blood platelet aggregation studies to identify the patients at risk for thrombosis or bleeding.

Hemorrhagic and thrombotic complications in patients with myeloproliferative diseases

OBJECTIVE

To correlate the incidence of hemorrhage and thrombosis to bleeding time (BT) and platelet aggregation in 27 consecutive patients with myeloproliferative diseases (MPD).

DESIGN

Retrospective study.

SETTING

Public tertiary referral center.

PATIENTS

Eighteen patients with chronic myelogenous leukemia (CML), 5 with polycytemia vera (PV), 2 with essential thrombocytemia (ET) and 2 with idiopathic myelofibrosis (MF). Duke's BT and epinephrine-induced platelet aggregation were performed on the patients and on 10 healthy individuals.

RESULTS

Eleven patients presented symptoms (41%):9 with hemorrhage (33%) and 5 with thrombosis (19%). There were less symptomatic patients in the CML group (28%) than in the other MPD (67%), without statistical significance (Fisher, p = 0.06). Duke's BT was longer in symptomatic patients (Mann-Whitney, p < 0.05). Platelet aggregation was abnormal in 7 patients (26%) and 71% of them were symptomatic (Fisher, p = 0.07).

CONCLUSIONS

The high incidence of bleeding and thrombosis in patients with MPD was related to prolonged BT, but not to platelet aggregation abnormalities.

Bleeding time and platelet function in essential thrombocythemia and other myeloproliferative syndromes

Bleeding time (BT) and platelet function tests have been widely used in patients with essential thrombocythemia (ET), with the aim to support diagnosis and to identify laboratory predictors of haemorrhagic and thrombotic complications. BT is significantly prolonged in 7-19% of ET patients and several functional abnormalities have been observed in platelet structure, biochemistry and survival. However, the attempt to relate these in vivo and in vitro platelet dysfunctions with diagnosis or clinical sequelae has been generally disappointing. Therefore, BT and platelet function tests are currently not recommended in the initial evaluation or during the follow-up of patients with ET, unless in the setting of a clinical or biological study. A noteworthy exception is represented by a subset of patients characterized by very high platelet count (> 1500 x 10(9)/L) and bleeding symptoms, who can have an acquired von Willebrand disease. In these cases, prolonged BT and abnormal multimeric pattern of von Willebrand factor are useful for diagnosing and monitoring this acquired hemorrhagic disease. BT and platelet function tests should be included in the baseline evaluation of ET patients enrolled in prospective clinical trials aiming assess their predictive role on clinical end-points.

Thrombosis and hemorrhage in oncology patients

As outlined in this review, patients with cancer may harbor many alterations of hemostasis. These are multifaceted and must be considered when trying to control hemorrhage or thrombosis in cancer patients. Also, hemorrhage or thrombosis is often the final fatal event in many patients with metastatic solid tumor or hematologic malignancies. Patients with malignancy present a major clinical challenge in this new era of oncologic awareness and more aggressive care, which has led to prolonged survival for patients and a longer time frame during which these complications may develop. Therefore, these complications are occurring more commonly. It is important to realize that these alterations of hemostasis exist and must be approached in a sequential and logical manner with respect to diagnosis; only in this way can responsible, efficacious, and rational therapy be delivered to patients. By far the most common alteration of hemostasis in malignancy is that of hemorrhage associated with thrombocytopenia, either drug-induced, or radiation-induced, or from bone marrow invasion. Hemorrhage resulting from DIC, however, is also quite common and may present as hemorrhage, thrombosis, thromboembolus, or any combination thereof. Many antineoplastic drugs and radiation therapy may lead to or significantly enhance hemorrhage in patients with malignancy. Thrombosis, also commonly seen in patients with malignancy, is often a manifestation of low-grade DIC. When approaching the patient with malignancy and either hemorrhage or thrombosis, all the potential defects in hemostasis must be considered, defined from the laboratory standpoint, and treated in as precise and logical manner as possible.

Platelet function defects associated with hemorrhage or thrombosis

Platelet dysfunction, especially acquired forms, is a common cause of hemorrhage, especially when associated with trauma or surgery. Although the hereditary platelet function defects are generally quite rare, hereditary storage pool disease is common enough to be suspected in an individual, usually a child, with characteristic historical and clinical findings. The acquired platelet function defects, especially those resulting from drugs, are common and should promptly be suspected in patients developing easy and spontaneous bruising, mild-to-moderate mucosal membrane hemorrhage, or unexplained bleeding associated with trauma or surgery. The template bleeding time is generally useful as a screening test of platelet function, but a normal template bleeding time, in the face of a suggestive history, suggestive clinical findings, or in a patient frankly bleeding, is not reliable, and platelet aggregation or lumiaggregation should be done in appropriate clinical situations. Also, prolongation of the template bleeding time is an unreliable predictor of clinical bleeding propensity. The mainstay of therapy for almost all these defects, if bleeding is significant, is the liberal infusion of appropriate numbers of platelet concentrates. The acquired platelet function defects should also be managed by attempts to treat or control the underlying disease, if possible, and offending drugs or potentially offending drugs should immediately be stopped.

Electrokinetic behaviour and surface sialic acid status of blood platelets in essential thrombocythaemia (ET)

We have previously reported, for platelets from patients with idiopathic thrombocytopenic purpura, that there was in increased electrophoretic mobility that was related to their increased sialic acid content. Heterogeneity in the circulating platelet pool of patients with essential thrombocythaemia (platelet counts 600-1000 x 10(9)/l) has also been investigated by preparative continuous flow electrophoresis (CFE). The surface charge-dependent separation profiles of all the patients' platelets showed marked anodal shifts compared with the profiles of platelets from age- and sex-matched control subjects separated under identical conditions. The increase above normal in the net electronegativity of the patients' platelets could not be accounted for by differences in surface neuraminidase-labile or total platelet sialic acid content.

An abnormal pattern of multiple platelet function abnormalities and increased thromboxane generation in patients with primary thrombocytosis and thrombotic complications

Platelet aggregation (PA) induced by ADP, collagen and epinephrine, plasma levels of beta-thromboglobulin (beta TG) and thromboxane B2 (TXB2) and serum TXB2 generation were studied in 11 patients with primary thrombocytosis (7 with essential thrombocythaemia and 4 with polycythaemia vera) and compared with 16 healthy subjects. 5 patients suffered from peripheral vascular ischaemia and another 3 had venous thrombosis, but none had bleeding complications. The patients showed an abnormal pattern of platelet function and of thromboxane generation distinct from the healthy subjects in three aspects. a) Shape change was 5-26 times greater, the lag-time of collagen PA was 2.3-2.9 times longer and the extent of epinephrine PA was nil or very low. ADP- or collagen-induced PA was also reduced (p less than 0.02). b) Plasma TXB2 generation (corrected to a normal platelet concentration) stimulated by the three PA inducers was within the range of the healthy subjects in spite of the reduced extent of PA. c) Plasma beta TG level and serum TXB2 generation (both corrected to a normal platelet concentration) were 2.9-7.1 times higher (p less than 0.001) indicating enhanced in vivo platelet activation and possibly increased thrombin generation. These abnormalities were not detected in another 4 patients with secondary thrombocytosis. The abnormal pattern of platelet function and thromboxane generation can be a useful laboratory method in the evaluation of patients with primary thrombocytosis. It might also explain the thrombotic complications which occurred in 8 of the patients in a manner such that increased or normal TXB2 generation overcomes the reduced extent of PA. In this respect, the pronounced serum TXB2 synthesis might be a marker of intravascular thrombosis.

Platelet function and interferon alpha-2a treatment in essential thrombocythaemia

The effects of interferon (IFN) alpha-2a treatment on platelet function were evaluated in 20 patients affected by essential thrombocythaemia (ET). Baseline data documented the well-known abnormalities of in vitro platelet aggregation and the constant presence of a delta-storage pool deficiency. The therapy in all patients reduced the platelet count, and in the majority of them caused a partial improvement of in vitro platelet aggregation. Although the mean intraplatelet ADP level improved during treatment, it always remained below the normal range documenting persistence of the delta-storage pool deficiency. The plasma beta-TG levels, which initially were high, significantly decreased during treatment, but the beta-TG ratio and the platelet beta-TG values always remained within the normal range--this suggests an absence of platelet activation either before or during therapy. Our results demonstrate that, despite significantly reducing the platelet count, IFN alpha-2a treatment only partially corrects the qualitative platelet abnormalities in ET.

Platelets of patients affected with essential thrombocythemia are abnormal in plasma membrane and adenine nucleotide content

The adenine nucleotides present in distinct cellular compartments of platelets of 27 patients affected with essential thrombocythemia have been measured. In order to quantify granule-bound nucleotides and adenylic cytoplasmic pool, platelets have been stimulated with thrombin or treated with increasing digitonin concentrations, respectively. Among patients, we have identified two groups: 12 patients (Group 1) had normal platelet level of ATP and ADP both in dense granules as well as in cytoplasmic pool. The other patients (Group 2) had granule ATP and ADP significantly lower and ATP/ADP ratio significantly higher than controls. In these patients an increase in hypoxanthine level, derived from metabolic ATP degradation occurring during stimulation, was observed. In addition, in the latter patients an increased resistance of plasma membrane to digitonin was shown, suggesting that membrane fluidity should be reduced owing to a modified cholesterol/phospholipid ratio.

Qualitative platelet defects in chronic myeloproliferative disorders: evidence for reduced ATP secretion

19 consecutive untreated patients with chronic myeloproliferative disorders and thrombocytosis were subjected to comprehensive platelet function tests including platelet aggregometry. 12 patients had essential thrombocythaemia (ET) and 7 patients had polycythaemia vera (PV). Bleeding time was normal. Arachidonic acid, collagen and ristocetin aggregation were abnormal only in a minority of patients, whereas ADP aggregation was impaired in 16 out of 19 patients. The most conspicuous findings were abolished second-wave adrenalin aggregation, increased ADP aggregation threshold, and markedly reduced ATP secretion during collagen-induced aggregation. This triad of qualitative platelet defects seems to be a good diagnostic marker of chronic myeloproliferative disease with thrombocytosis.

Budd-Chiari syndrome and thrombosis of other abdominal vessels in the chronic myeloproliferative diseases

Of 501 patients with chronic myeloproliferative diseases (c-MPD) 18 developed thrombosis of major abdominal vessels including 6 with hepatic vein thrombosis (Budd-Chiari syndrome). The complication was seen in 14 of 140 (10%) patients with polycythemia vera (PV), 3 of 23 (13%) patients with essential thrombocythemia (ET), 1 of 106 (1%) patients with idiopathic myelofibrosis (IMF), and none of 232 patients with chronic myelogenous leukemia (CML). Leading symptoms and signs were abdominal pain, progressive splenomegaly, widening abdominal girth, ascites, venous collaterals, and nausea and vomiting. The diagnostic modalities with highest specificity were angiography and explorative laparotomy. A causal relationship between the thrombotic event and hematocrit, thrombocyte count, or hemostatic abnormalities at the time of diagnosis could not be established. Detailed laboratory tests of platelet function and coagulation and fibrinolytic parameters of 5 surviving patients did not show any specific defect. Despite medical and surgical intervention, 39% of the patients died within 2 months after diagnosis of the thrombosis. The majority of the survivors developed further complications like liver cirrhosis with portal hypertension and esophageal varices or the short bowel syndrome after extensive bowel resection for mesenterial infarction.

Platelet function in myeloproliferative disorders: characterization and sequential studies show multiple platelet abnormalities, and change with time

Bleeding and thrombosis are well known major causes of morbidity and mortality in patients with myeloproliferative disorders (MPD) but the relationship between these clinical events and the commonly found platelet function abnormalities have not been established. In this study we performed simultaneous laboratory evaluations in 54 patients with MPD to investigate abnormalities in platelet aggregation and cyclooxygenase activity, the latter by using an in vitro aspirin inhibition test; the studies were repeated in 22 patients 1-27 months later. We have found platelet hyper- and hypofunction co-existing in some patients (9/54), and change of platelet function during the course of the disease (7/22) with platelet hypofunction being the only constant abnormality over time. These results may explain the lack of correlation between the clinical events and the limited assessment of platelet function in the hitherto published studies, and also suggest the need for repeated evaluations to properly assess the relative risk for bleeding and thrombosis.

Polycythaemia and thrombocythaemia in the elderly

The investigation of elderly patients presenting with raised PCV values has been described. Suitable clinical and laboratory investigation enables the separation of those with a raised red cell mass (RCM) into three groups: primary proliferative polycythaemia (PPP), secondary polycythaemia and idiopathic erythrocytosis. Those patients with a raised PCV but normal RCM either have apparent polycythaemia (normal plasma volume) or relative polycythaemia (low plasma volume). PPP is a clonal disorder with a peak incidence in the elderly. It commonly presents with vascular occlusive symptoms/signs involving larger vessels, both arterial and venous. The microvasculature may also be involved, particularly when there is associated thrombocythaemia. Effective treatment is required to minimize the future vascular occlusive incidence and diminish the complication rate of surgery if it is ever required. Both the PCV and the platelet count, if elevated, should be adequately controlled. 32P is probably the simplest treatment and is very effective, but venesection and intermittent low-dose busulphan is equally satisfactory in the co-operative patient with good peripheral veins. Secondary polycythaemia may arise from a variety of causes, particularly from arterial hypoxaemia and renal lesions. Occasionally, more than one pathology is identified in the elderly patient. Lung disease is the most common cause of hypoxaemia. Venesection may be indicated in those patients with excessively raised PCV values. The term idiopathic erythrocytosis should only be used for patients who have been adequately investigated. These patients most commonly present with ischaemic or vascular occlusive symptoms/signs. Relative polycythaemia may be caused by fluid loss, but generally the origin of the low plasma volume is not established. Apparent polycythaemia may represent a physiological variant or a stage before the development of a definitely raised RCM. The management of idiopathic erythrocytosis, and relative and apparent polycythaemia, should initially involved removal of known risk factors if present (e.g. hypertension) with the addition of venesection in selected patients. Reactive thrombocytosis in the elderly is most commonly due to malignant disease of chronic infection. The high platelet count is usually asymptomatic, and antiplatelet therapy is rarely required. Primary thrombocythaemia (PT) is a clonal myeloproliferative disorder similar to PPP. The finding of splenomegaly, abnormal platelet morphology or function helps to separate PT from reactive thrombosis. PT most commonly presents with digital or transient cerebral ischaemia or haemorrhage.(ABSTRACT TRUNCATED AT 400 WORDS)

Intermittent melphalan in the treatment of essential thrombocytosis with haemorrhage or thrombosis

178 episodes of essential thrombocytosis with symptoms of haemorrhage or thrombosis, were treated in 15 patients with melphalan (5 mg/m2 orally during 4 d). An average reduction in the platelet count of 77% was achieved by oral melphalan in 14 responding patients. 1 patient appeared to be refractory to oral therapy, but a decrease of the thrombocyte count was achieved after intravenous administration of melphalan. All responding patients experienced a relief of the thrombocytosis-associated clinical symptoms. Reduction of the thrombocyte count persisted for 3-4 wk.

The myelodysplastic syndromes--a study of haemostatic function and platelet ultrastructure

The myelodysplastic syndromes (MDS) are characterised by dysplastic marrow and cytopenia. Clinically detectable bleeding is uncommon and usually attributed to thrombocytopenia. We have investigated some aspects of haemostatic function in 17 patients with MDS and compared the results with findings from 17 control patients matched for age and sex. No specific disorder of blood coagulation or fibrinolysis was identified. The main abnormalities observed in the patients were: prolongation of the bleeding time which was greater than could be explained on the basis of thrombocytopenia in 13 patients; absent, or severely impaired platelet aggregation in response to collagen in 7 patients; impaired platelet production of malondialydehyde when stimulated with collagen and abnormal release of 14C-5 hydroxytryptamine in 5 patients; and abnormalities of ultrastructure in all 5 patients whose platelets were viewed by electron microscopy.

Platelet-associated IgG and IgM in myelofibrosis

Elevated levels of platelet-associated IgG and/or IgM were found in 15 of 18 patients with myelofibrosis (83%). All but 5 patients with elevated PAIg had active disease. The amounts of PAIg were not correlated to either S-Ig, platelet count or spleen size. Levels of PAIgG well above the normal range were especially found in patients with short duration of disease and/or a transitional myeloproliferative state. It is debated whether immune-mediated platelet dysfunction may be of importance for the development of bone marrow fibrosis, mediated by the release of platelet-derived growth factors in the bone marrow. Elevated PAIg may also contribute to abnormal haemostasis and thrombocytopenia in myelofibrosis.

Functional significance of the platelet alpha2-adrenoceptor: studies in patients with myeloproliferative disorders

Platelet alpha-adrenoceptor status was examined in 35 patients with myeloproliferative disorders (MPD) and 35 normal controls by means of radioligand binding studies with 3H-yohimbine (3H-YOH) and in vitro platelet function tests. A group of 'adrenaline insensitive' MPD patients identified in the functional studies were found to be identical to normal controls and other MPD patients with respect to their alpha 2-adrenoceptor status as assessed by the binding studies. Possible explanations for the dissociation between radioligand binding studies and functional responses in the platelet are discussed.

An altered platelet granule glycoprotein in patients with essential thrombocythemia

The protein profiles of washed platelets from nine patients with essential thrombocythemia were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In four patients, an additional protein band (reduced Mr of 170,000) was clearly identified in both unstimulated platelet preparations and thrombin-released supernatant fractions. This band was also evident, though to a lesser extent, in three more patients, but it could not be located in the two remaining patients nor in any of ten controls. Subsequent characterization of the 170,000 reduced protein in one patient indicated that (a) it was glycosylated, as judged by periodic acid-Schiff staining, and (b) that native protein was a disulfide-linked multimer (possibly trimeric), which (c) partially bound to the activated platelet plasma membrane in the presence of calcium, and (d) was immune precipitated by anti-glycoprotein G antisera. The combined evidence is consistent with the 170,000 reduced protein being a modified form of the normal subunit of the platelet alpha-granule constituent, glycoprotein G (also termed thrombospondin and thrombin-sensitive protein).

Thrombohaemorrhagic complications in 101 cases of myeloproliferative disorders: relationship to platelet number and function

A series of 101 consecutive patients with chronic myeloproliferative disorders including polycythaemia vera, chronic myelogenous leukaemia, idiopathic myelofibrosis and essential thrombocythaemia have been studied. The aim was to establish the incidence of thrombotic and haemorrhagic complications and the possible role played by platelet number and function. The total incidence of haemostatic complications was 21% and the platelet functional tests investigated (platelet aggregation, generation of malondialdehyde, endogenous serotonin, beta-thromboglobulin and platelet coagulant activity) were of little help for predicting these clinical complications.

The possible value of platelet aggregation studies in patients with increased platelet number

ADP, adrenalin and collagen platelet aggregation studies were performed in 54 patients with elevated platelet counts: 38 patients showed primary thrombocythemia and 16 secondary thrombocytosis. Patients with primary thrombocythemia (78.7%) showed a decrease aggregation pattern while in patients with secondary thrombocytosis platelet aggregation response was entirely normal. An increase in platelet aggregation was obtained in four patients with primary thrombocythemia. The platelet aggregation response did not appear to be related to circulating platelet number. A relationship between increased platelet aggregation and the occurrence of thrombosis was demonstrated. Similarly, a correction between impaired platelet aggregation and bleeding was also present. These results emphasize the diagnostic value of platelet aggregation studies in patients with elevated platelet number.

Defective platelet aggregation and increased platelet turnover in patients with myelofibrosis and other myeloproliferative diseases

In 9 patients with myeloproliferative diseases (MPD) (6 with myelofibrosis, MF, 1 with Ph1 positive chronic granulocytic leukaemia, CGL, 1 with primary eosinophilia, PE, 1 with pre-leukaemia syndrome, preL) collagen, epinephrine, and ADP-induced aggregation, N-ethylmaleimide-induced malondialdehyde (MDA) production, beta-thromboglobulin (beta-TG) plasma levels, and platelet turnover were studied. Collagen-induced aggregation was found to be normal in 7 patients, absent in 1, and reduced in 1. In all but 3 patients, aggregation with ADP was markedly reduced. Epinephrine-induced aggregation was decreased in 7 patients. No difference was found between mean MDA production in MPD (3.21 +/- 0.50 nmol/10(9) PLTs) and in control group of 21 normal subjects (3.04 +/- 0.26 nmol/10(9) PLTs). Mean beta-TG levels were significantly higher (P less than 0.01) in MPD patients (165.00 +/- 28.29 ng/ml) than in healthy controls (81.76 +/- 14.63 ng/ml). Mean platelet production half-time was significantly shorter in MPD (2.48 +/- 0.24 d) than in the control group (3.43 +/- 0.17 d), after adjustment for age by covariance analysis (P less than 0.005). Our data do not indicate an abnormal prostaglandin synthesis and are consistent with the hypothesis that a disseminated intravascular platelet aggregation might take place in MPD patients.

Platelet dysfunction in myeloproliferative syndromes

The most common abnormality of the platelets in 43 patients with a variety of myeloproliferative syndromes was impaired or absent aggregation when stimulated with collagen and adrenaline. Eight unselected cases studied in more detail showed a normal prostaglandin synthesis pathway as evidenced by normal aggregation with arachidonic acid and the production of normal amounts of malonyldialdehyde. Mixing experiments with aspirin-tested platelets showed correction of the abnormal adrenaline and collagen responses and confirmed that the nature of the defect was different from that induced by aspirin. Stimulation of "myeloproliferative" platelets with thrombin after blocking the prostaglandin pathway with aspirin resulted in reduced aggregation, indicating either a deficiency of the storage pool of adenine nucleotides in the platelets or an abnormality of a membrane receptor for thrombin.

Platelet function in preleukaemia

Platelet function was studied in 17 patients with preleukaemia and the results were compared with those of 28 patients with other chronic myeloproliferative disorders. The test pattern included bleeding time (Ivy), platelet retention (Hellem II), PF-3 activity and availability after exposure to ADP and kaolin, and ADP-, epinephrine-, collagen- and ristocetin-induced aggregations. Platelet function was frequently impaired in patients with preleukemia. The defects were similar to those found in other myeloproliferative disorders. The most consistent finding was defective aggregation. Patients with thrombocytosis and/or with increased amounts of megakaryocytes in the bone marrow had fewer defects in platelet function. Retention defect was more common in patients with hypolobulated megakaryocytes, especially in those having a specific marker, the 5q- chromosome, in their bone marrow cells.

The effect of acetyl salicylic acid and dipyridamole on thromboembolic complications in splenectomized patients with myelofibrosis

The effect of combined treatment with acetyl salicylic acid and dipyridamole on thrombic phenomena was studied in splenectomized patients with an aggressive form of myelofibrosis. 3 of these patients had thrombotic episodes, shortened platelet survival and an abnormal platelet aggregation pattern. The treatment with antiplatelet drugs resulted in a decreased platelet utilization as evidenced by clinical improvement and an increasing platelet concentration.

Platelet storage pool deficiency and prostaglandin synthesis in chronic granulocytic leukaemia

Platelet function was evaluated in eight patients with chronic granulocytic leukaemia (CGL), seven Ph1 positive and one Ph1 negative. Seven of the eight patients' platelets had an absence of the second wave of adrenaline induced aggregation on at least one occasion, while five had impaired collagen aggregation. The platelets of all seven patients with abnormal responses to adrenaline, aggregated with arachidonic acid, thus ruling out a cyclo-oxygenase deficiency. A marked decrease in the ADP, serotonin, and dense body content of platelets was found in all five patients evaluated. Mixtures of CGL patient platelets with platelets from normal donors who had ingested aspirin gave a normal biphasic response to adrenaline. Normal release of the storage pool contents from aspirin treated platelets was shown by stirring a mixture of CGL platelets and 14C-serotonin labelled aspirin treated platelets with adrenaline. The CGL platelets alone or in the mixture produced malondialdehyde in response to adrenaline. These experimental results suggest that CGL platelets have a storage pool deficiency but can synthesize prostaglandins and thromboxanes in response to arachidonic acid and adrenaline.

A fatal myeloproliferative syndrome in a family with thrombocytopenia and platelet dysfunction

Three siblings with a lifelong history of a bleeding disorder and thrombocytopenia died from a myeloproliferative disease. In 2, the terminal event resembled juvenile chronic myelogenous leukemia, and in the third, the diagnosis was acute monocytic leukemia. A family study revealed that the mother and 5 other siblings had a variety of hematologic abnormalities. These included chronic thrombocytopenia, abnormal platelet function, elevated concentrations of HgbF or serum vitamin B12, and low leukocyte alkaline phosphatase (LAP) scores either singly or in combination. At the time of study, none had evidence of malignancy. Members of this family have a myeloproliferative disorder that has the potential for terminating in nonlymphocytic leukemia, a combination of events which appears not to have been reported previously.

Changes in distribution of platelet membrane glycoproteins in patients with myeloproliferative disorders

Glycoproteins have been discovered to be important to platelet function both in normal and pathological states. We have studied membrane glycoprotein patterns in 16 patients with various myeloproliferative disorders. There was an abnormal ratio of glycoprotein I:glycoprotein IV in patients with myeloproliferative disease compared with controls. There was no discernible correlation between glycoprotein pattern and aggregation response or platelet count, but patients with megathrombocytes had higher values for glycoprotein IV than those without megathrombocytes. These experiments suggest that patients with myeloproliferative disorders may have alterations in membrane glycoproteins that could alter platelet function.