Platelet function in essential thrombocythemia. Decreased epinephrine responsiveness associated with a deficiency of platelet alpha-adrenergic receptors

Platelet distribution width for differential diagnosis of thrombocytosis

Differential diagnosis of thrombocytosis is not always obvious. The routine clinical chemistry laboratory classically provides only limited help in distinguishing between reactive thrombocytosis (RT) and autonomous thrombocytosis, where platelet production escapes normal regulatory processes, and which is seen in myeloproliferative diseases (MPD) such as essential thrombocythemia and polycythemia vera. We explored the clinical use of platelet distribution width (PDW) in the differential diagnosis of thrombocytosis. During a 3-month period, 250 patients presenting with a platelet count >500 × 109/L were studied; 174 were classified as having RT, 42 had a diagnosis of MPD, and 34 patients were excluded because they had a hemopathy different from MPD, and either did or did not present a known etiologic factor for RT. First, we determined that in the RT group the value of PDW was closely linked to both mean platelet volume (MPV) and platelet count (PLT) (PDW = 79.5 − 0.005 PLT − 3.5 MPV; r = 0.848, R2 = 0.720). Therefore a new parameter, PDWresidual, was defined (PDWresidual = PDWobserved − PDWexpected). Second, the discrimination between reactive and autonomous thrombocytosis obtained with PDWresidual was compared with that obtained with either PDW, MPV, or PLT. PDWresidual proved much more powerful than each of the other parameters used separately: 76% of MPD patients had a PDWresidual above the 95th percentile value of the RT population and none of the MPD patients had a PDWresidualbelow the 50th percentile. Thus, the combined interpretation of PLT, MPV, and PDW through the use of a PDWresidualappears highly useful in the differential diagnosis of thrombocytosis. Also, through simple modeling, more information can be drawn from parameters such as PDW that hitherto were mostly discarded as being without clinical interest.

Platelet alpha 2-adrenergic receptors in hypercholesterolemia: relationship between binding studies and epinephrine-induced platelet aggregation

BACKGROUND

Platelets isolated from patients with hypercholesterolemia are more sensitive in vitro to various aggregating agents, including epinephrine, than those isolated from normocholesterolemic subjects. Increased platelet reactivity is one mechanism that may explain the enhanced risk of thromboembolism in hypercholesterolemia. This study assessed whether platelet hyperreactivity to epinephrine in hypercholesterolemia is associated with higher alpha 2-adrenergic receptor density or affinity for epinephrine.

METHODS

Platelet aggregation and binding studies, with use of [3H]yohimbine as ligand, were performed on platelets isolated from 30 patients with type IIa hypercholesterolemia and 23 control subjects.

RESULTS

Platelet aggregation in response to epinephrine was significantly higher in patients with hypercholesterolemia than in control subjects. A statistically significantly higher alpha 2-adrenergic receptor density was observed in a subgroup of 13 patients with hypercholesterolemia than in 13 sex- and age-matched control subjects (280 +/- 61 and 230 +/- 49 fmol/mg protein respectively; p < 0.03), but no difference was observed in receptor affinity for the ligand. In these subgroups plasma total and levels of low-density lipoprotein (LDL) cholesterol were inversely correlated with platelet aggregation but directly correlated with platelet receptor density.

CONCLUSION

Platelet alpha 2-adrenergic receptor density is increased in hypercholesterolemia and directly correlates with plasma total and levels of LDL cholesterol, providing at least a partial explanation for the enhanced platelet response to epinephrine that is observed in hypercholesterolemia.

Megakaryocytes and platelets in myeloproliferative disorders

Increased megakaryocyte (MK) proliferation in bone marrow is a feature common to the three Ph-negative myeloproliferative disorders (MPDs), i.e. essential thrombocythaemia (ET), polycythaemia vera (PV), and myelofibrosis with splenic myeloid metaplasia (MMM), and to chronic myelocytic leukaemia (CML). Enlarged MKs with multilobulated nuclei and cell clustering in close proximity are the hallmark of all the Ph negative MPDs. Clonality of haematopoietic cells, based on X chromosome inactivation, can now be studied in a majority of female patients in all nucleated cell fractions as well as in platelets. Cytofluorometric studies have demonstrated a shift towards higher ploidy classes in PV and ET MKs which may be useful in discriminating between both primary and reactive thrombocytosis and CML patients which show a significant shift to lower MK ploidy values. The role of MK proliferation on the evolution of myelofibrosis common to MPDs has been firmly established. Implication of platelet-derived growth factor (PDGF) in myelofibrosis has already been demonstrated. More recently transforming growth factor beta (TGF beta) synthesized and secreted by MK has been implicated in fibroblasts stimulation. A significant increase in circulating colony-forming units of MKs (CFU-MK) has been repeatedly observed in MPDs as well as a spontaneous MK colony formation in a majority of ET patients. Hypersensitivity to thrombopoietin (TPO) in relation to a functional defect of the TPO-MPL pathway may play a major role in spontaneous MK growth. There is no currently available test of platelet functions able to predict the risk of occurrence of thrombotic or haemorrhagic complications in MPD patients. However, the role of platelet activation in the pathogenesis of ischaemic erythromelalgia has been established and a correlation between presenting haemorrhagic manifestations and platelet counts in excess of 1000 x 10(9)/l has been found.

Signal transduction system in epinephrine stimulated platelets; comparison between epinephrine sensitive and insensitive platelets

We recently reported the high prevalence of impaired platelet responsiveness only to epinephrine in healthy Japanese. This abnormality was associated with a 50% decrease in the number of alpha 2-adrenergic receptors. Platelets from non-responders (NR) do not undergo secondary platelet aggregation even after exposure to 100 microM epinephrine, but they can potentiate the effect of ADP to provoke platelet aggregation. To further define the nature of the defect and to delineate controversial steps of epinephrine stimulated signal transduction, a signaling pathway of epinephrine was investigated in platelets from NR and R(normal responder to epinephrine). In a unique particle counting apparatus, epinephrine initially triggered the formation of small platelet aggregates composing of 10-1000 cells from both R and NR, but the aggregates became larger (4600 > cells) only in platelets from R. Thus, platelets from NR lack the ability to form larger aggregates. A similar defect was reproduced by treating normal platelets with aspirin. In the presence of fibrinogen, platelets from NR lacked phospholipase A2 activation, determined by arachidonic acid liberation in the presence of inhibitors to cyclooxygenase and lipoxygenase. In the absence of fibrinogen, aggregation and phospholipase A2 activation were not evident in R and NR. The surface expression of GPIIb/IIIa was markedly decreased in platelets from NR after stimulation by epinephrine, in comparison with those from R. The resting level and epinephrine stimulated increase in cAMP were not significantly different between NR and R. Incubating R platelets with a half saturating dose of yohimbine rendered them insensitive to epinephrine. These results indicated that the impaired platelet aggregation induced by epinephrine was due to the impaired surface exposure of glycoproteins GPIIbIIIa integral to the activation of phospholipase A2, which requires the full and normal occupancy of the alpha 2-adrenergic receptor by epinephrine.

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.

Disorders of platelet function

Qualitative platelet disorders are described and reviewed above. The acquired platelet function defects are very common, and sometimes result in hemorrhage, especially in association with trauma or surgery. However, the specific biochemical defect is absent, and no characterized platelet abnormalities have been recognized. On the other hand, the hereditary qualitative platelet defects are rare, but the platelet abnormalities are characteristic. The study of these patients had led to an increased understanding of the normal primary hemostatic mechanism. Recently, the molecular basis analysis of the platelet defects has been developed. This will help us understand the molecular events involved in platelet adhesion and aggregation.

Prevalence of impaired responsiveness to epinephrine in platelets among Japanese

The responsiveness of platelets only to epinephrine was markedly impaired in 23/140 (16%) healthy Japanese. The impaired responsiveness was not altered by changes in time and environment. Circulating level of catecholamines did not affect the responsiveness of platelets to epinephrine. A pilot family study indicated a possible familial nature of the defect. 3H methyl-yohimbine binding studies indicated that this defect was due to the decreased number of alpha 2 adrenergic receptor. Despite the defect, the potentiating effect of epinephrine on platelet aggregation stimulated by a low dose of ADP was normal. This abnormality is not apparently associated with any bleeding disorders and the clinical implication is unknown at present. It is, however, essential to acknowledge the prevalence of such defect in pursuing research on platelets stimulated by epinephrine.

Essential thrombocytosis: underemphasized cause of large-vessel thrombosis

PURPOSE

The purpose of this study was to describe the clinical course of patients seen with large-vessel thrombosis in association with essential thrombocytosis (ET).

METHODS

This study was a retrospective review of all patients treated for large-vessel thrombosis caused by ET during a 2-year period at University of Washington teaching hospitals.

RESULTS

Five patients presented with arterial (femoral-popliteal-tibial: aortic), portal (two cases), or systemic venous (inferior vena cava) thrombosis and required operation. Two were known to have ET; in three others ET was diagnosed after operation when platelet counts persistently in excess of 500,000/mm3 were noted. The diagnosis of ET was established in each case by ruling out causes of reactive thrombocytosis and (in the three new cases) by evidence for megakaryocyte hyperplasia on bone marrow biopsy. Platelet counts in all five patients were reduced to normal levels by cytoreductive therapy, and no further thrombotic episodes have occurred during 18 months (mean) of follow-up. During this 2-year period ET accounted for more large-vessel thrombotic complications in our institutions than all other more frequently described hypercoagulable states combined.

CONCLUSIONS

ET is an underemphasized cause of large-vessel thrombosis.

Treatment of essential thrombocythemia with anagrelide

Essential thrombocythemia (ET) is a myeloproliferative disorder characterized by persistent elevation in platelet count. It is a rare disorder in children, and children who have symptoms require treatment. We report the successful use of anagrelide, with few toxic effects, in the treatment of three children with ET.

Issues in the diagnosis and management of essential thrombocythemia

OBJECTIVE

To summarize the current trends in the diagnosis and management of essential thrombocythemia (ET) and to discuss the treatment of young and pregnant patients with ET.

DESIGN

We review our experiences in the diagnosis and management of ET.

MATERIAL AND METHODS

A definitive diagnosis of ET at initial examination is seldom possible because of the low incidences of associated clonal cytogenetic abnormalities and palpable splenomegaly. The criteria of the Polycythemia Vera Study Group for the diagnosis of ET are provided, as are the clinical and laboratory features that help to distinguish ET from reactive thrombocytosis.

RESULTS

Patients with ET have an almost normal life expectancy if thrombohemorrhagic complications are controlled. Although a previous history of thrombosis is an established risk factor for further episodes, the adverse effects of extreme thrombocytosis and age are less well defined. Determining which patients require therapy is controversial. The management of young or pregnant patients necessitates special considerations.

CONCLUSION

Until additional data become available, no strong recommendations can be given in support of or against specific therapy for asymptomatic young patients. We favor treatment in asymptomatic patients with cardiovascular risk factors but not in asymptomatic women who are pregnant or are of childbearing age.

Heterogeneous abnormalities of platelet dense granule ultrastructure in 20 patients with congenital storage pool deficiency

Studies on platelet dense granule structure were carried out in 20 patients with various types of congenital storage pool deficiency (SPD), including 15 with specific deficiencies of dense granules and dense granule substances (delta-SPD), and five with combined deficiencies of dense and alpha-granules (alpha delta-SPD). Dense granules were identified by their high affinity for uranyl ions (uranaffin reaction), by their ability to accumulate the fluorescent dye mepacrine, and by their inherent electron opacity on unfixed, unstained whole mount preparations. By all these methods, dense granules were markedly decreased in seven albino patients with the Hermansky-Pudlak syndrome (HPS) variant of delta-SPD. These findings suggest that the basic defect in these patients is a specific abnormality in organelle development which prevents the formation of an intact granule structure, a quantitative abnormality which may differ from that in animals with related pigment disorders. In contrast, eight non-albino patients with delta-SPD had, on average, only a slightly reduced number of uranaffin-positive and mepacrine-positive granules, but a shift in uranaffin-granule distribution towards those lacking a dense core ('empty granules'), suggesting a more qualitative type of dense granule defect. These results are consistent with previous evidence suggesting a decreased uptake of ATP across the granule membrane in delta-SPD. In addition, on whole mounts, these patients' platelets contained substantial numbers of electron dense chains and clusters which contained P and Ca, but with a P/Ca ratio less than that of typical dense granules, and which were retained, along with a larger amount of ATP, after thrombin treatment of the platelets. The various findings in these patients raise the possibility that these structures may represent microvesicles, derived from the Golgi apparatus, which provide a transport mechanism for concentrating adenine nucleotides and calcium in dense granules and which is impaired in some patients with SPD. Additional defects may account for the more extensive granule abnormalities observed in alpha delta-SPD.

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.

Inherited platelet-storage pool deficiency associated with a high incidence of acute myeloid leukaemia

A family with an inherited bleeding disorder extending over four generations, and multiple cases of myeloblastic and myelomonoblastic leukaemia was studied. Ten members of the family had, by history, a haemorrhagic diathesis. There were three documented cases of myeloblastic leukaemia, two documented cases of myelomonoblastic leukaemia and two more cases of leukaemia by history. In four of the cases the bleeding diathesis clearly antedated the leukaemia, in two by many years. The bleeding disorder is characterized by a long bleeding time, abnormal platelet aggregation, low platelet ADP and decreased numbers of platelet dense bodies consistent with a dense granule storage pool deficiency. The number of dense granules was decreased by immunofluorescence employing quinacrine or using an antibody to the dense granule membrane protein, granulophysin, confirming an absolute decrease in dense granule numbers rather than the presence of empty granule sacs. This congenital storage pool deficiency is associated with a high incidence of acute myeloid leukaemia in this family.

Thrombotic and hemorrhagic complications in essential thrombocythemia. A retrospective study of 103 patients

A retrospective study of 103 patients with essential thrombocythemia was carried out to evaluate the incidence of thrombohemorrhagic complications and establish whether there were any correlations between these events and clinical or laboratory data. At onset or during the course of the disease, 26 patients (25.2%) presented thrombotic and 12 (11.6%) hemorrhagic complications: among the latter, six patients had gastrointestinal bleeding during antiaggregant therapy. No significant correlations were observed between thrombohemorrhagic complications and platelet count, age, sex, platelet function, bleeding time, or therapeutic regimen. However, there was a statistically significant correlation between a positive patient history for thrombotic events and an increase in thromboses. In agreement with other authors, it is believed that the best approach in asymptomatic patients is strict surveillance without treatment. Chemotherapy and/or treatment with antiaggregant agents should be reserved for symptomatic patients or patients with a positive history for thrombotic events.

Basal and induced prothrombinase expression in platelets from patients with essential thrombocythaemia (ET)

Both the basal and the collagen plus thrombin-stimulated prothrombinase activities have been measured in platelets from eight patients with essential thrombocythaemia (ET). On a mean basis these activities were significantly lower than the values recorded for a group of age and sex matched control subjects. When the Ca2+ ionophore A23187 was substituted for the agonist mixture the induced expression of prothrombinase activity was essentially the same for the patient and control groups. It is suggested that the defect in prothrombinase expression seen with ET platelets may reside in either membrane signal transduction processes concerned with Ca2+ mobilization or in Ca2+ sensitive cytoskeletal control of membrane phospholipid topography.

Deficient elevation of the cytoplasmic calcium ion concentration by epinephrine in epinephrine-insensitive platelets of patients with myeloproliferative disorders

Elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i) by epinephrine and epinephrine-induced inhibition of prostaglandin E1 (PGE1)-stimulated cyclic adenosine monophosphate (cAMP) accumulation were assessed in platelets from three groups of subjects; normal controls (NS, n = 11) and patients with myeloproliferative disorders whose platelets were either sensitive (ES, n = 9) or specifically insensitive (El, n = 7) to the aggregatory effect of epinephrine. The inhibition by epinephrine of cAMP accumulation in the platelets exposed to 500 nM PGE1 was not significantly different between the three groups. Therefore, despite the defective aggregation response to epinephrine, platelets from the El group seemed to retain normal response, which was attained through alpha 2-adrenergic receptors, guanine nucleotide binding regulatory protein, and the adenylate cyclase system. However, in aequorin-loaded, washed platelets, the epinephrine-stimulated rise in [Ca2+]i showed significant decrease in the El group compared with the other groups (P less than 0.01). Thus the mechanism for the impaired aggregation response to epinephrine in platelets from the El group could include the defect that exists in the pathway from receptor binding of epinephrine to the aggregation response through [Ca2+]i elevation.

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.

Platelet membrane abnormalities in myeloproliferative disorders: decrease in glycoproteins Ib and IIb/IIIa complex is associated with deficient receptor function

The number and functional activity of membrane glycoproteins (GP) Ib and IIb/IIIa were investigated in platelets from 11 patients with myeloproliferative disorders (MPD). Three patients had essential thrombocythaemia, two had chronic myeloid leukaemia and six had polycythaemia vera. The numbers of GPIb and GPIIb/IIIa molecules were detected on the platelet surface using different 125I-labelled monoclonal antibodies. The functional properties of GPIb and GPIIb/IIIa were evaluated using purified 125I-labelled asialo von Willebrand factor (vWF) and purified 125I-labelled fibrinogen, respectively, in a binding assay. Binding of the anti-GPIIb/IIIa antibody was decreased by 40% in almost all patients studied and, when measured, it was accompanied by decreased fibrinogen binding to activated platelets. Binding of anti-GPIb antibodies to platelets was also slightly decreased or virtually the same in eight out of 11 patients. The decrease correlated with decreased binding of asialo vWF. The increased plasma glycocalicin levels, measured in four patients, depended on the high platelet count. Scatchard analysis revealed normal receptor binding affinity for all ligands tested in all but one patient. In this report we demonstrate that abnormalities in the concentrations of GPIIb/IIIa membrane proteins are commonly present in patients with MPD, while a decrease in GPIb concentration is also seen, although in fewer patients. These abnormalities are accompanied by a concurrent decrease in the respective receptor functions. These findings may explain part of the haemorrhagic tendency often encountered in MPD.

Slowly progressive ischemic stroke as first manifestation of essential thrombocythemia

We report a case of essential thrombocythemia, the only clinical manifestation of which consisted of neurologic symptoms, including anomic aphasia, tactile and painful hypesthesia in the right hand, headache, and Gerstmann syndrome, with a relatively benign and slowly progressive clinical course. Neuroradiologic examination disclosed a large ischemic area in the left temporoparietal region. Cerebral angiography revealed an occlusion of the cortical branches of the left middle cerebral artery with total sparing of the carotid vessel. These findings are discussed in relation to the possible pathogenetic mechanisms of the vascular occlusion due to abnormal platelet function in essential thrombocythemia.

[Megakaryocytic myelosis--clinical aspects, morphology and platelet function]

The study reviews 22 patients, aged between 19 to 73 years, with megakaryocytic myelosis. In the course of the disease 11 patients presented haemorrhagic manifestations, 12 patients thrombotic complications, and 6 patients the association of haemorrhage and thrombosis. The maximum platelet counts ranged from 524 to 2700 x 10(9)/l. The bone marrow showed a conspicuous megakaryocytic proliferation with polyploidy of the nuclei, giant forms and clusters. Marked alterations of erythro- and granulopoiesis were excluded. There was no evidence for a reactive thrombocytosis in any case. Patients with thrombocythaemia due to megakaryocytic myelosis (n = 14), with secondary thrombocytosis of various origin (n = 16), and a control group of healthy donors (n = 20) were investigated with respect to the aggregation behaviour and the total calcium content of blood platelets. In 9 of 14 patients with megakaryocytic myelosis platelet rich plasma did not respond to epinephrine (15 mumol/l), a concentration which induced at least weak aggregation in 14 of 16 patients with secondary thrombocytosis and also in healthy subjects. In patients with megakaryocytic myelosis the mean extent of aggregation induced by epinephrine, collagen or adenosine diphosphate was significant lower as compared to controls whereas in patients with secondary thrombocytosis in most cases this parameter did not differ significantly from that of controls. The total calcium content of platelets was significantly lower in both groups of patients as compared to controls. In 14 patients with megakaryocytic myelosis the concentration of the glycoprotein (GP) IIb-IIIa complex was estimated by crossed- and rocket-immunoelectrophoresis and found to be decreased in 8 of them.(ABSTRACT TRUNCATED AT 250 WORDS)

Multimeric composition of plasma von Willebrand factor in chronic myeloproliferative disorders

In chronic myeloproliferative disorders (CMPD) thrombohaemorrhagic complications occur occasionally in association with thrombocytosis. We studied the multimeric composition of plasma von Willebrand factor (vWf) in 15 patients with polycythaemia vera (PV), 12 with essential thrombocythaemia (ET) and eight with primary myelofibrosis (PMF). The relative content of large (multimer band greater than or equal to 11) multimers calculated by densitometer scan following SDS-agarose gel electrophoresis was 18.5 +/- 4.4% (mean +/- SD) in normal controls, 8.3 +/- 7.9% in PV, 8.1 +/- 4.6% in ET and 19.6 +/- 6.7% in PMF. The patients with PV and ET but not PMF had a significantly lower percentage of large multimers than normal controls (P less than 0.001). The relative content of large multimers was negatively correlated with WBC and platelet count (P less than 0.02 each) in PV. It was negatively correlated with platelet count (P less than 0.005) and was positively correlated with a ratio of ristocetin cofactor/vWf antigen (RCof/vWf:Ag) (P less than 0.01) in ET. These results indicate that acquired defects of vWf are quite common in PV and ET but not in PMF. In addition, some CMPD patients with high platelet counts completely lacked large multimers. The negative correlation of the relative content of large multimers with platelet count suggests that large multimers may be preferentially consumed during thrombocytosis or degraded by protease(s) from increased blood cells.

Preleukemic syndromes and other syndromes predisposing to leukemia

The myelodysplastic and myeloproliferative syndromes are syndromes in childhood that may precede leukemia. Clinical and biologic features are reviewed in this article. Although rare, they offer an unique opportunity to observe the evolution of leukemia and give clues that are helping us to understand the leukemogenic process.

Essential thrombocythemia. Clinical characteristics and course of 61 cases

Sixty-one patients with essential thrombocythemia (ET) were followed from 1974 through 1987 at the Medizinische Poliklinik. Fifty-one patients (84%) presented with thromboembolic complications, and eight patients (13%) with hemorrhages. In seven patients (12%), a thrombocytosis was detected accidentally. Disturbances of the microcirculation (67%), mainly of the fingers and toes (53%), were the most frequent thromboembolic symptoms. The mean age of all patients was 58 years (male patients, 61 years; female patients, 56 years). The average platelet count at diagnosis was 897,000/microliter. The average maximal platelet count was 1.231 X 10(6)/microliter (range, 500,000/microliter to 4 X 10(6)/microliter). Seventy-two percent had a moderate leukocytosis (average, 12,400/microliter), 34% a splenomegaly, 29% a hepatomegaly. Signs of hypermetabolism were infrequent, lactate dehydrogenase (LDH) and uric acid elevations, if present, were moderate. Bleeding time and viscosity were normal in most patients. Spontaneous platelet aggregation was increased in 81% of patients (n = 40). Platelet aggregation studies with the aggregation inducing substances adenosine diphosphonate (ADP), platelet activating factor (PAF), thrombin, collagen, and adrenalin showed hypoaggregation in most patients. Adrenalin-induced aggregation distinguished best between ET-patients and reactive thrombocytosis showing hypoaggregation in all ET-patients tested (n = 16) and in none of 22 controls. Bone marrow studies were performed in 57 patients. The histologic studies (done in 49 patients) were consistent with a chronic myeloproliferative disorder in all cases. In 41 cases (84%) the picture of a megakaryocytic myelosis was found, in 12 of these a granulocyte-rich form of megakaryocytic myelosis. Cytologic studies only (eight patients) did not differentiate ET well from reactive thrombocytosis. Platelet aggregation studies and bone marrow histology may be of help in the diagnosis of difficult cases of thrombocytosis. The Philadelphia status was negative in all cases studied (14 patients). Fourteen patients died. The causes of death were thromboembolic complications in probably 11 and acute leukemia in two patients. The probability of 10-year survival is 64% after a mean follow-up time of approximately 5 years. It appears that considering the average age of ET patients at diagnosis, life expectancy is close to normal.

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.

[Thrombocyte function in essential thrombocythemia and reactive thrombocytosis]

Blood of 16 patients with essential thrombocythemia (ET), 9 patients with reactive thrombocytosis (RT) and 13 healthy persons was used for platelet aggregation studies. When the aggregation was induced with adenosine diphosphate (0.01 microM), collagen (0.1 micrograms/ml) or platelet activating factor (PAF 0.5 microM) the plasma of the patients with ET showed significantly decreased aggregation (35%-44% of the value for the control groups). Independent of inhibitors of platelet aggregation, thrombin (0.05 U/ml) caused similar aggregation in healthy controls and patients with ET; patients with RT showed an increase aggregation. Adrenalin-induced aggregation discriminated best between patients with ET and controls. Adrenalin in concentrations ranging from 0.01 micrograms/ml to 100 micrograms/ml caused comparable dose-related amounts of aggregation in healthy controls and patients with RT. Over the whole concentration range, patients with ET showed significantly decreased aggregation (28%-34% of the value for the control groups). This difference proved to be independent of the influence of inhibitors of platelet aggregation. Though concentrations of alpha1-acid glycoprotein never reached inhibitory levels in the plasma of patients with ET (n = 12) they were significantly higher compared with those in normal plasma (n = 12). Fibrinogen concentrations in plasma of ET-patients (n = 12) were in the normal range. Cellular adenosine 3'-5'-cyclic monophosphate concentrations in ET (n = 10) are comparable with normal values (n = 5). The significance of the results for diagnosis and better pathophysiological understanding of ET is discussed.

Acquired von Willebrand disease in patients with polycythemia rubra vera

Platelet function and factor VIII complex were evaluated in ten patients with polycythemia rubra vera. Seven patients showed abnormal epinephrine-induced aggregation. The intracellular concentrations of adenosine diphosphate (ADP) were below normal, and the ratio of adenosine triphosphate (ATP)/ADP was greater than normal. In four of eight cases, there was a decrease in ristocetin cofactor activity and a reduction in the slowly migrating forms of vWF:Ag on crossed immunoelectrophoresis. Defect of large multimers of vWF:Ag was also observed. The ratio of vWF:Ag to ristocetin cofactor was elevated in these patients. Plasma from the patients had no effect on normal plasma except in one case, in which isolated IgG appeared to cause inactivation of ristocetin cofactor. Treatment with 1-deamino-8-arginine vasopressin caused correction of the vWF abnormalities with rapid return of ristocetin cofactor to baseline in some patients. The present study shows that the alterations of multimeric structure of vWF occur in more than 50% of patients with polycythemia rubra vera and are in some part due to the inhibitor specific for vWF.

Essential thrombocythemias. Clinical evolutionary and biological data

This retrospective study reviewed 94 patients, aged 6 to 90 years, with thrombocythemia. The women/men ratio was 1.76. At onset or, less commonly, during the course of the disease, 45% of the patients presented hemorrhagic manifestations, 29% thrombotic complications, and only 14% the association of hemorrhage and thrombosis. The average platelet count was 1200 X 10(9)/1, with no difference according to sex or age. Platelet hypoaggregation was seen in practically all the cases (94%), although myelofibrosis was less frequent (54%). The frequency of hemorrhages increased when the platelet count was above 1000 X 10(9)/1 (P less than 0.01), but the occurrence of thrombosis was correlated neither with platelet count nor with thrombopathy. Survival time was lengthy: 80% of survival (standard error 6%) was observed at 100 months. Transformation to acute leukemia was observed in five patients. Because the disease course is most often prolonged, therapeutic measures must be conservative: anti-aggregating drugs in small doses, and chemotherapy beginning with nonalkylating agents.

Acquired von Willebrand disease and storage pool disease in chronic myelocytic leukemia

Platelet function was evaluated in 20 patients with chronic myelocytic leukemia (CML), all Ph positive. Seven showed abnormal epinephrine-induced aggregation, while four had impaired both ADP- and collagen-induced aggregation. The platelets of all patients aggregated with arachidonic acid, thus ruling out cyclooxygenase or lipoxygenase deficiency. The intracellular concentrations of ATP and ADP were significantly below normal, and the ratio of ATP/ADP was greater than normal in all 12 patients. ATP released from platelets by Lumi-aggregometer was reduced. In four patients with abnormal ristocetin-induced aggregation, vWF:Ag, RCoF, and FVIII:C were all reduced. No significant inactivation of factor VIII was induced in normal plasma by incubation with patient's plasma. The crossed immunoelectrophoretic analysis revealed that vWF:Ag in these patients was mainly composed of more anodic component as compared with that of normal plasma. The ratio of vWF:Ag/RCoF was significantly greater than normal. A marked increase of factor VIII and a rapid return of vWF:Ag and RCoF to the baseline after the 1-deamino-8-arginine vasopressin (DDAVP) infusion were observed. Transient increase in vWF:Ag after the infusion of DDAVP appeared with less anodic forms and in the same relative proportion as that in normal plasma. The present study shows that in some patients with CML storage pool disease occurs with acquired von Willebrand disease.

Essential thrombocytosis with the Philadelphia chromosome (Ph')

Essential thrombocytosis is a myeloproliferative disease not known to have consistent cytogenetic abnormalities. A 46-year-old black woman with essential thrombocytosis and a Philadelphia chromosome is reported. Iron deficiency and tuberculosis were present but when effectively treated did not result in resolution of thrombocytosis. Megakaryocytic hyperplasia of bone marrow, abnormal platelet function studies and a compatible clinical state suggested the diagnosis of essential thrombocytosis. The diagnostic criteria for other myeloproliferative diseases were not met. The Philadelphia chromosome was consistently obtained from bone marrow preparations. We conclude that the Philadelphia chromosome may be found in essential thrombocytosis as well as other, previously reported, myeloproliferative diseases.

Acquired von Willebrand syndrome due to an inhibitor specific for von Willebrand factor antigens

A patient with acquired von Willebrand syndrome associated with polycythemia rubra vera is described. Her plasma factor VIII procoagulant activity (67 U/dl) and factor VIII-related antigen (117 U/dl) were normal but no von Willebrand factor activity could be detected. Factor VIII crossed immunoelectrophoresis revealed decreased levels of less anodic polymeric forms of factor VIII. Mixture of her plasma or immunoglobulin G (IgG) fraction with normal plasma resulted in complete recovery of factor VIII activity and related antigen but no measurable von Willebrand factor activity, confirming the presence of an unique inhibitor. The limited specificity of this inhibitor to antigenic sites solely on the von Willebrand portion of the factor VIII bimolecular complex is distinct from all previous reports of this syndrome. This unique inhibitor offers a molecular probe to examine the von Willebrand factor: platelet interaction.

Simultaneous measurement of epinephrine-induced platelet aggregation in 14 plasma samples

A method is described for the simultaneous measurement of epinephrine-induced platelet aggregation in 14 different plasma samples in 15 min. It is based upon discontinuous registration of platelet aggregation and computer evaluation of the data. The samples are placed in holders mounted over magnetic stirring bars in a 37 degrees C water bath and the extinction is measured by removing the samples one after the other, placing them in a Braun Universal Aggregometer and returning them to their holders in the water bath. The time required to reach 37% of maximal aggregation was chosen as the evaluation criterion. It sufficed for the determination of aggregation sensitivity. This method for the first time permits measurement of a complete titration curve rapidly and under identical conditions and can be used to show the influence of a wide range of aggregation inducers and the concurrent effects of inducers plus various blocking agents. A correlation between aggregation sensitivity and alpha 2-receptor binding capacity in platelets, measured by competitive radioactive binding, was established in samples from 10 healthy volunteers. One group exhibited high aggregation sensitivity coupled with high alpha 2-binding capacity and the other showed low sensitivity with low binding capacity.

Simple linear regression in medical research

This article discusses the method of fitting a straight line to data by linear regression and focuses on examples from 36 Original Articles published in the Journal in 1978 and 1979. Medical authors generally use linear regression to summarize the data (as in 12 of 36 articles in my survey) or to calculate the correlation between two variables (21 of 36 articles). Investigators need to become better acquainted with residual plots, which give insight into how well the fitted line models the data, and with confidence bounds for regression lines. Statistical computing packages enable investigators to use these techniques easily.

Variations in circulating catecholamines fail to alter human platelet alpha-2-adrenergic receptor number or affinity for [3H]yohimbine or [3H]dihydroergocryptine

A series of studies were performed to determine the relationship between physiologic levels of circulating plasma norepinephrine and epinephrine and human platelet alpha-2 binding site number and the affinity (KD) of these sites for antagonist radioligands. In one study, alpha-2-adrenergic binding site number and affinity were compared using both [3H]yohimbine and [3H]dihydroergocryptine as radioligands. There was good absolute and relative comparison for binding site number, but only a relative relationship for KD. In 46 normal subjects, there was no significant relationship between site number or KD and age, plasma epinephrine, or plasma norepinephrine concentration. Even after plasma epinephrine was raised nearly 20-fold by means of an intravenous infusion for 4 h in seven normal subjects, neither sites (608 +/- 68 vs. 567 +/- 120 sites/platelet) nor KD (2.01 +/- 0.94 vs. 2.14 +/- 1.15 nM) were significantly changed. Similarly, neither sites (445 +/- 55 vs. 421 +/- 53 sites/platelet) nor KD (1.44 +/- 0.29 vs. 2.10 +/- 0.75 nM) were significantly changed in six normal subjects when plasma norepinephrine levels increased during oral administration of prazosin for 1 wk. Thus, in a cross-sectional analysis and after a change in plasma catecholamine concentrations, there was no relationship in normal subjects between platelet alpha-2 binding site number or affinity of these sites for antagonist radioligands and the circulating catecholamine levels to which the platelets were exposed. In a group (n = 7) of patients who lack epinephrine-induced platelet aggregation due to abnormal thrombopoiesis, binding site number was decreased (304 +/- 36 vs. 572 +/- 29 sites/platelet, P less than 0.001) and KD tended to be greater (8.69 +/- 2.44 vs. 5.40 +/- 0.31 nM, P = NS) than in normal subjects (n = 46), despite having similar plasma catecholamine levels. There was no difference in binding site number (491 +/- 116 sites/platelet) and KD (5.61 +/- 0.84 nM) in patients (n = 5) with autonomic insufficiency and low levels of upright plasma norepinephrine when compared with the normal subjects. Two patients were examined before and after the removal of a pheochromocytoma. Their binding site number and KD were normal before the operation and essentially unchanged after the tumor removal and fall of plasma catecholamines. Thus, this study demonstrates that within the physiologic and pathophysiologic range of plasma catecholamines (in men), there is no relationship between the circulating catecholamine concentration and either platelet alpha-2 adrenergic binding site number or the affinity of these sites for antagonist radioligands.

Human platelet alpha 2-adrenoceptors: relationship between radioligand binding studies and adrenaline-induced aggregation in normal individuals

Using the alpha 2-adrenoceptor selective radioligand [3H]yohimbine maximum binding capacities (Bmax), dissociation constants (KD), and the affinity (KI) of adrenaline for the binding sites were measured in platelets obtained from a group of 42 normal individuals. These results were compared with the efficacy of adrenaline induced aggregation in platelet rich plasma in the same subjects. Wide interindividual variation was found in Bmax values as measured in whole platelets (sites/platelet) or platelet lysates (fmol/mg protein) and in KI values for adrenaline displacement of [3H]yohimbine binding. Adrenaline's ability to induce platelet aggregation measured as the concentration required to achieve half maximal aggregation assessed from dose-response curves showed similar interindividual variation. No correlation was found, however, between alpha 2-adrenoceptor status as assessed by radioligand binding studies and the functional studies. These results suggest that the present understanding of the relationship between alpha 2-adrenoceptor occupation and platelet aggregation may be incorrect.