Megakaryocytes and platelets in immune thrombocytopenic purpura

The Double Hazard of Bleeding and Thrombosis in Hemostasis From a Clinical Point of View: A Global Assessment by Rotational Thromboelastometry (ROTEM)

Hemostasis is a complex dynamic process involving bleeding and thrombosis as two end-points. Conventional coagulation tests which are measured in plasma examine only isolated portions of the coagulation cascade, thereby giving no information on important interactions essential to the clinical evaluation of hemostatic function. Thromboelastography (TEG), originally described in 1948 has improved over the decades and become a valuable tool of coagulation testing because of the limitations of standard coagulation tests. TEG is a technique that provides data about the entire coagulation system, from the beginning of clot formation to fibrinolysis, involving both cellular and plasma components of hemostasis. Rotational thromboelastometry (ROTEM) which evolved from TEG technology overcome several limitations of classical TEG while maintaining a good correlation with conventional TEG determination. ROTEM analyses are useful for rapid assessment of global clotting function in various clinical situations including liver transplantation, cardiac surgery, obstetrics, trauma, hemophilia and idiopathic thrombocytopenic purpura. ROTEM has been also reported to be useful in identifying various hypercoagulable conditions including major surgery, malignancy, Behcet’s disease and apheresis. Further developments in ROTEM based transfusion strategies may also reduce transfusion requirements and improve clinical outcomes by optimizing the administration of blood components. This is a literature review of ROTEM including its technique, interpretation and specially clinical applications in different scenarios of bleeding and thrombotic disorders.

Can thrombelastography be a new tool to assess bleeding risk in patients with idiopathic thrombocytopenic purpura?

Thrombelastography (TEG) analyses the status of blood coagulation including abnormalities associated with low platelet count. The aim of this study was to investigate the changes in TEG parameters in idiopathic thrombocytopenic purpura (ITP) patients. Thirty nine patients with ITP (platelet count < 100 × 103  µl⁻¹) were included in the study. Age-matched 17 patients with thrombocytopenia due to chemotherapy were selected as a control group. Platelet count was positively correlated with maximum clot formation (MCF) in INTEM (r = 0.716, p < 0.001) and MCF in EXTEM (r = 0.679, p < 0.001); negatively correlated with clot formation time (CFT) in INTEM (r = -0.755, p < 0.001) and CFT in EXTEM (r = -0.585, p < 0.001) in ITP patients. Platelet count was positively correlated with MCF in INTEM (r = 0.776, p < 0.001) and MCF in EXTEM (r = 0.878, p < 0.001); negatively correlated with CFT in INTEM (r = -0.627, p < 0.001) in control group. Receiver operating characteristic curves to describe the critical platelet count and fibrinogen level that affect MCF revealed 31 × 103 µl⁻¹ and 375 mg dl⁻¹ as cut-off values, respectively. In conclusion, ROTEM determines the contribution of fibrinogen and platelets to clot strength in patients with ITP. MCF appears to be the most important TEG parameter in predicting bleeding in ITP patients that makes TEG superior to other hemostatic tests.

Effect of platelet count on secretion capacity: formulization and use of the formulae for evaluation of platelet secretion in thrombocytopenic patients

The correlation between platelet count and bleeding time is nonlinear. The bleeding time prolongs more prominently as platelet count decreases toward 10 000 microl(-1); however, it becomes stable near 100 000 microl(-1). Clinical observations suggest that platelet functional capacity may also play a role in bleeding complications during thrombocytopenia. However, no routine method has been described for evaluation of platelet function during thrombocytopenia. To test if platelet functional capacity is affected by the cell count, as suggested by the platelet count-bleeding time correlation. To evaluate lumiaggregometry as a possible tool for studying platelet functions and prediction of bleeding in thrombocytopenic patients. Collagen-induced ATP release was studied in different dilutions of 22 healthy platelet-rich plasmas. The relationship between platelet count and ATP release was formulized. ATP release was also tested in 24 thrombocytopenic (10 000-50 000 microl(-1). ) patients, and the results were compared with expected levels derived from the formulae. ATP release increased in a cubic fashion as platelet count elevated. ATP secretion values were within normal limits or increased in patients with idiopathic thrombocytopenic purpura. However, some patients with megakaryocyte deficiency had a secretion defect. ATP secretion was decreased in four out of seven patients with bleeding symptoms compared with no persons without bleeding (P = 0.003). Platelet functional capacity is affected by the cell count. Lumiaggregometry is potentially useful in evaluating platelet functions during thrombocytopenia.

Anti-beta2-glycoprotein I in childhood immune thrombocytopenic purpura

Immune thrombocytopenic purpura (ITP) etiology is not clarified. Phospholipid antigen antibodies (aPls) occur in ITP patient sera. We studied predictive values of elevated anti-beta2-glycoprotein I (anti-beta2-GP1) or anticardiolipin antibody (aCl) concentrations for secondary ITP detection, comparing levels with steroid therapy responsiveness in three groups of children and adolescents. Participants' antinuclear antibodies, aCls (IgM, IgG) and anti-beta2-GPI (IgG) were assessed. Significantly higher aCl (IgM), aCl (IgG) and anti-beta2-GPI (IgG) mean concentrations occurred in chronic ITP cases compared with acute or control cases. Of chronic ITP cases, 77.8% showed elevated IgG aCl serum concentrations, and all presented increased IgG anti-beta2-GPI serum levels. Significant positive correlation between increased levels of IgG anti-beta2-GPI and increased IgG aCl serum concentrations was determined; these increased IgG concentrations significantly correlated with steroid therapy resistance. A total of 76.1% of ITP cases had positive aPls (all chronic ITP cases, five acute ITP cases). Elevated aCl or anti-beta2-GPI serum IgG isotype concentrations occurred in all nine splenectomized ITP children with positive aPls (three showed increased IgM aCl levels). Follow-up of the initially studied ITP children (2000-2004) revealed 16.7% developed clinical and laboratory criteria of systemic lupus erythrematosus (one acute ITP in remission, six chronic ITP); elevated IgG aCl serum concentrations were found at study start in these seven cases, and six had increased anti-beta2-GPI. IgG classes of both aCls and anti-beta2-GPI may be determinant cofactors for the developing risk of antiphospholipid syndrome or autoimmune diseases in ITP. Great attention should be paid to both assays as predictors for steroid therapy response.

Immune complex-associated thrombocytopenic purpura syndrome in sexually mature Göttingen minipigs

Eleven cases of thrombocytopenic purpura (TP) in sexually mature male or female Göttingen minipigs occurred sporadically over 3 1/2 years in a closed breeding colony protected by strict barrier conditions. Typical clinical signs of TP, including extensive subcutaneous haemorrhages, were seen in all affected animals. Haematological abnormalities included marked thrombocytopenia and anaemia. A consistent histopathological finding was the presence of membranoproliferative lesions in the renal glomeruli. Immunohistochemically, glomerular deposits were positively labelled for complement factor C1q and often also for immunoglobulins. Bone marrow findings consisting of increased numbers of immature and apoptotic megakaryocytes were compatible with a state of increased platelet consumption. Based on the combined presence of thrombocytopenia and renal immune complexes, it is suggested that the syndrome was related to a type III hypersensitivity reaction. However, further studies are needed to verify this hypothesis.

Anti-platelet antibodies associated with the Canale-Smith syndrome bind to the same platelet glycoprotein complexes as those of idiopathic thrombocytopenic purpura patients

The Canale-Smith syndrome (CSS) is an inherited disease characterized by massive lymphadenopathy, hepatosplenomegaly and systemic autoimmunity to erythrocytes and platelets. Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disease in which approximately 60-80% of patients have anti-platelet antibodies directed against specific platelet glycoprotein complexes (GPCs) located on their membrane: GP IIb/IIIa, GPIb/IX, and GPIa/IIa. Almost all (95-100%) of the antibody-positive patients have antibodies directed against GPIIb/IIIa alone, or in combination with other glycoprotein targets. Our objective was to determine the specificities of the anti-platelet antibodies in CSS patients. The detection of anti-platelet antibodies was performed using a commercially available ELISA, the Pak-AUTO (GTI, Brookfield, WI), in which highly purified GPIIb/IIIa, GPIb/IX, and GPIa/IIa are immobilized on microtitre plates, incubated with serum or plasma, and subsequently developed with an antihuman polyclonal immunoglobulin. Of 14 CSS patients tested, 11 (79%) had anti-platelet antibodies in their serum directed toward at least one of the three major GPC, nine (82%) of which were against GPIIb/IIIa alone or in combination. Antibodies detected in the sera of ITP patients had similar specificities. No such antibodies were detected in samples from 25 consecutive normal controls. These results demonstrate that a genetically defined defect in lymphocyte apoptosis results in a humoral autoimmune response with anti-platelet specificities very similar to the common idiopathic form of autoimmune thrombocytopenia.

Pregnancy complicated by Evan's syndrome

Evan's syndrome was initially diagnosed in a 26-year-old pregnant patient. Following the introduction of high dose steroid therapy, the patient developed possible disseminated gonococcal infection which was followed by preterm labor and abruptio placentae. A cesarean delivery was performed at the 34th week of pregnancy following platelet infusion. While the infant survived, the mother had delayed postpartum hemorrhage.

Mathematical analysis of the relative contributions of decreased production and increased peripheral destruction in idiopathic thrombocytopenic purpura and implications in splenectomy

We utilize a model of platelet concentration kinetics and bone marrow production based on three terms (a constant loss term, a random loss term and a higher order loss term) to compare a hypoplastic bone marrow patient and a patient with Idiopathic Thrombocytopenic Purpura (ITP) for the same platelet concentration. We compare this model to published data and show that in many ITP patients there is an overall decrease in platelet production. However, for almost all cases of ITP there is an increase in peripheral platelet destruction, even in those cases where total bone marrow production is less than that in a normal individual or is severely depressed. We are able to graphically depict the variable contributions of decreased production and increased peripheral destruction in patients with ITP and hence give insight into their relative contributions in a given patient. We apply a unique feature of our model, the newly postulated destruction term proportional to the platelet concentration squared (the higher order loss term), to explain cases of antibody negative ITP. Application of our model to data on patients splenectomized as treatment for ITP shows promise in predicting which patients are likely to respond.

Correlation of platelet Fc gammaRIIA polymorphism in refractory idiopathic (immune) thrombocytopenic purpura

Fc gammaRIIA, a low affinity receptor for IgG, is a polymorphic molecule: Fc gammaRIIA-HH131, Fc gammaRIIA-HR131 and Fc gammaRIIA-RR131. This polymorphism influences the efficiency of the receptor to bind with IgG2. Recent reports on altered distribution amongst individuals with heparin-induced thrombocytopenia (HIT) prompted us to examine the Fc gammaRIIA polymorphism in a cohort of patients with refractory idiopathic (immune) thrombocytopenic purpura (ITP), in whom severe disease had required them to undergo splenectomy. 29 post splenectomy ITP individuals and 61 normal controls were investigated. Polymerase chain reaction (PCR) and a Southern blotting technique were used to determine the Fc gammaRII polymorphism. Although the distribution of the allotypes of Fc gammaRIIA in the control population was similar to that found in other European studies of Caucasian populations (15 (25%) HH131; 35 (57%) HR131; 11 (18%) RR131), the patient group was skewed towards the RR131 allotype which has least efficiency for IgG2 binding (3 (10%) HH131; 12 (42%) HR131; 14 (48%) RR131; P<0.005). These findings suggest that Fc gammaRIIA polymorphisms may be implicated in the pathophysiology of ITP or may be responsible for modulating the immune response in this heterogeneous autoimmune disease.