Heparin-induced thrombocytopenia and thrombosis

The effect of antisense oligodeoxynucleotide to rat troponin T (TnT) mRNA on its expression in differentiated rat L6 myotubes in culture was examined. The target sequence following the initiation codon was between nucleotides 83 and 97 and is found in all mRNAs produced from the f-TNT gene. Our studies showed that chimeric oligomer with one phosphorothioate linkage at the 3'-end was considerably more resistant to nucleases than was a phosphodiester oligomer. The chimeric oligomer produced >50% inhibition of TnT polypeptide synthesis. Synthesis of myosin heavy chain (MHC), troponin I (TnI), and alpha and beta tropomyosins (Tm) was not inhibited by the anti-TnT oligomer. However, synthesis of alpha-actin and troponin C (TnC) was somewhat affected by this treatment. Furthermore, compared with the untreated control myotubes, the steady-state level of TnT mRNA was reduced by approximately 40%-50% in anti-TnT oligomer-treated myotubes. Cellular levels of three other muscle mRNAs, alpha-Tm, s-TnI, and alpha-actin were also reduced by approximately 30%-40%. In contrast, fast TnI, beta-Tm, and TnC mRNA levels were not significantly affected by this treatment. Therefore, inhibition of TnT synthesis in differentiated myotubes uncoupled the coordinated expression of muscle proteins.     

Heparin-induced thrombocytopenia: pathophysiology

We have used computer modeling of insulin 3-D structure and experimental data about action of site point mutation on insulin activity to design functionally important domain with signaling activity and synthesized peptide than might be sufficient for the binding to insulin receptor. The designed and synthesized peptide consist of ten residues and may be obtained in two forms: oxidized and reduced (with or without disulfide bond). The synthesized decapeptide peptide represents functionally important site for binding to the insulin receptor. Amino acid residues at position 1-8 correlate with B-chain of insulin at position (B19-B26). Residues at position 9.10 correlate with A-chain at position A-10-A21. This peptide was tested with cell culture L-929 (glucose uptake) in comparison with bioactive commercial peptide (R-G-FF) and insulin. It was shown that synthesized peptide exhibit biological activity at molar concentration 0.01-1 mkM. Our results successfully demonstrate the synthetic insulin fragment have insulin-like biological activity.     

Heparin-induced thrombocytopenia and thrombosis

Although heparin is widely used as the injectable anticoagulant of choice, it has several potential shortcomings. These include heparin resistance, excessive bleeding, allergic reactions, and, with longterm use, occasional osteoporosis or alopecia. Perhaps the most notorious complication is heparin-induced thrombocytopenia and thrombosis (HITT); although unusual, it often results in major morbidity or death. Until recently, reliable diagnostic tests and anticoagulation alternatives have not been widely available. After a review of the pharmacology of heparin and related drugs, advances in the prevention, diagnosis, and treatment of this problem are discussed.     

Heparin-induced thrombocytopenia and thrombosis: presentation after cardiopulmonary bypass

Heparin-induced thrombocytopenia and thrombosis syndrome was diagnosed in a 63-year-old woman 11 days after coronary artery bypass grafting. Her only presenting complaints were incisional leg pain and vague chest discomfort. The syndrome was suspected when her platelet count was found to be 37,000/microL. A subsequent ventilation-perfusion lung scan showed findings highly probable for pulmonary embolism. An inferior venacavogram obtained before a pulmonary angiogram revealed a large retrohepatic thrombus at the right atrial junction. The patient was successfully treated with the defibrinogenating agent ancrod (Arvin). A diagnosis of heparin-induced thrombocytopenia and thrombosis syndrome should be considered and heparin therapy should be avoided in patients with low platelet counts who have been previously treated with heparin.     

Heparin-induced thrombocytopenia with thrombotic complications during prophylactic treatment with low-molecular-weight heparin

Heparin-induced thrombocytopenia is very uncommon with low-molecular-weight heparin, especially when given for prophylaxis of venous thromboembolism. In two of the four published cases, with thrombotic complications, thrombocytopenia may have been related to cross-reactivity between unfractionated heparin and low-molecular-weight heparin. We report one patient who received low-molecular-weight heparin for prophylaxis against venous thromboembolism without any previous injection of unfractionated heparin, and experienced thrombocytopenia with thrombotic complications. Heparin-induced thrombocytopenia was confirmed by several laboratory assays. This observation emphasizes the need for platelet count monitoring during low-molecular-weight heparin therapy.     

Heparin-induced thrombocytopenia, paradoxical thromboembolism, and other side effects of heparin therapy

Although several new anticoagulant drugs are in development, heparin remains the drug of choice for most anticoagulation needs. The clinical effects of heparin are meritorious, but side effects do exist. Important untoward effects of heparin therapy including heparin-induced thrombocytopenia, heparin-associated osteoporosis, eosinophilia, skin reactions, allergic reactions other than thrombocytopenia and alopecia will be discussed in this article.     

Heparin-induced thrombocytopenia: new insights into the impact of the FcgammaRIIa-R-H131 polymorphism

Heparin-induced thrombocytopenia (HIT), a severe complication of heparin treatment, can be associated with new thrombotic complications. HIT antibodies activate platelets via the platelet Fcgamma-receptor (FcgammaRIIa), which carries a functionally relevant polymorphism (FcgammaRIIa-R-H131). The effect of this polymorphism on the clinical manifestations of HIT is controversial. We determined prospectively the FcgammaRIIa-R-H131 genotypes in 389 HIT patients, in 351 patients with thrombocytopenia or thrombosis due to causes other than HIT and without detectable HIT antibodies, and in 256 healthy blood donors. For this purpose, a novel nested sequence-specific primer-polymerase chain reaction (SSP-PCR) was developed. FcgammaRIIa-R/R131 was found to be overrepresented in the HIT patients (27%) compared with the control groups (non-HIT patients [21%] and blood donors [20%]). In a subgroup of 122 well-characterized HIT patients, the genotype distribution in patients presenting with thrombocytopenia only was compared with that of patients who developed thromboembolic complications. The frequency of FcgammaRIIa-R/R131 among patients with thrombotic events was significantly elevated (37% v 17%; P = .036). Our results indicate that genotype distribution can be correlated to the clinical outcome of patients with HIT. We speculate that the reduced clearance of immune complexes in patients with the FcgammaRIIa-R/R131 allotype causes prolonged activation of endothelial cells and platelets, thus increasing the risk for thrombotic complications.     

Heparin-induced thrombocytopenia: IgG-mediated platelet activation, platelet microparticle generation, and altered procoagulant/anticoagulant balance in the pathogenesis of thrombosis and venous limb gangrene complicating heparin-induced thrombocytopenia

Until recently, the confusing clinical profile of HIT and the widespread unavailability of reliable diagnostic assays have conspired to produce under-recognition-if not frank skepticism-of the clinical importance of HIT. However, during the 1990s, HIT has emerged as one of the major-if not the most important-immunohematologic problems in clinical medicine. The clinical and laboratory investigations summarized here have contributed to a greater understanding of the frequency, clinical spectrum, pathogenesis, laboratory diagnosis, and-potentially-the prevention of this important drug allergy. Further, the demonstration of increased platelet procoagulant activity and, thrombin generation in HIT, together with insights into the pathogenesis of a new clinicopathologic syndrome (venous limb gangrene), help explain how a disorder characterized by IgG-mediated platelet activation can lead to such diverse clinical sequelae as venous thrombosis, pulmonary embolism, disseminated intravascular coagulation, and venous limb gangrene. These studies should lead to improved treatment of HIT (new emphasis on suppression of thrombin generation, eg, hirudin and its analogs), future avoidance of HIT (preparation of low-molecular-weight heparins and heparinoids that are less immunogenic), and a greater understanding of the interaction between platelet activation and procoagulant/anticoagulant processes.     

Fetal thrombocytopenia and its relation to maternal thrombocytopenia

BACKGROUND: Neonates with severe thrombocytopenia can have bleeding leading to death or lifelong residual defects. The predictors, frequency, and consequences of fetal thrombocytopenia are not known, nor is it known if there are maternal clinical features that could predict fetal thrombocytopenia. METHODS: We conducted a seven-year cross-sectional study in which platelet counts were determined in newborns' umbilical-cord blood and blood obtained from their mothers at consecutive deliveries in one obstetrical unit. The relations of the umbilical-cord platelet count to maternal risk factors were determined. RESULTS: Platelet counts were determined in blood samples from 15,471 mothers and 15,932 newborn infants. The cord-blood platelet count was less than 50,000 per cubic millimeter in 19 infants (0.12 percent; 95 percent confidence interval, 0.07 to 0.19 percent), whereas the platelet count was less than 150,000 per cubic millimeter in 6.6 percent of the mothers (95 percent confidence interval, 6.2 to 7.0 percent). One infant among those born to 756 mothers with incidental thrombocytopenia, 5 infants among those born to 1414 mothers with hypertension, and 4 infants among those born to 46 mothers with idiopathic thrombocytopenic purpura had cord-blood platelet counts between 20,000 and 50,000 per cubic millimeter. Only 6 infants (0.04 percent; 95 percent confidence interval, 0.01 to 0.08 percent) had cord-blood platelet counts of less than 20,000 per cubic millimeter; all their mothers were among the 18 whose 19 fetuses were at risk for neonatal alloimmune thrombocytopenia. Two of these infants had in utero intracranial hemorrhage. In addition, 3 infants born to these 18 women had cord-blood platelet counts between 20,000 and 50,000 per cubic millimeter; there was 1 stillbirth due to intracranial hemorrhage. CONCLUSIONS: Moderate-to-severe fetal thrombocytopenia is a rare event. The only severely affected neonates with morbidity or mortality due to this condition are those born to mothers with antiplatelet alloantibodies.     

Rifampicin-induced thrombocytopenia

Rifampicin occasionally causes thrombocytopenia when given as part of an intermittent regimen. A case is reported of severe thrombocytopenia developing after one dose of rifampicin, following a 4-month gap in daily therapy. The literature on rifampicin-induced thrombocytopenia is reviewed.     

Chlorpropamide-induced thrombocytopenia

Thrombocytopenia is a rare complication of chlorpropamide therapy. An immunological mechanism is generally held responsible, but has never previously been proved. In the present case the existence of such a mechanism has been established.     

Diltiazem-associated thrombocytopenia

Nine days after starting diltiazem therapy for new-onset atrial fibrillation, a patient's platelet count had diminished to 61 x 10(3)/mm3, and 2 weeks later the nadir was reached at 23 x 10(3)/mm3. No hypersensitivity reaction otherwise was noted, and other hematologic values were unaffected. The patient's platelet counts were not affected by platelet transfusions. Bone marrow examination showed normal to increased numbers of megakaryocytes, suggesting peripheral destruction. After discontinuing diltiazem and administering high-dose immunoglobulin infusions, the platelet count returned to normal. This case suggests an immune-mediated cause for thrombocytopenia after exposure to diltiazem.     

Rifampicin-induced immune thrombocytopenia

Rifampicin-induced thrombocytopenia is reported in three patients with pulmonary tuberculosis. All three patients gave a definite history of having had prior exposure to rifampicin. Immunological studies in all three patients showed the presence of antiplatelet antibodies, resulting in thrombocytopenia. Moreover, binding of these antibodies to the platelet membrane was more avid in the presence of rifampicin, thereby implicating the drug. The avidity of the rifampicin-dependent antibodies was demonstrated by platelet aggregation inhibition test, and estimation of the rifampicin-dependent antibody was done by studying the platelet-associated immunoglobulin [PAlgG] by ELISA which was also used to quantitate antiplatelet antibodies. Immunofluorescence test was also performed to detect antiplatelet antibodies.     

Splenunculectomy in recurrent thrombocytopenia

A 13-year-old boy developed thrombocytopenic purpura in 1953 which improved during 4 weeks of cortisone therapy. Following 13 years of intermittent symptoms the platelet count was found to be 8,000/mul. After splenectomy the patient was asymptomatic for 8 years, but had a recurrence of symptoms and thrombocytopenia in 1974. An initial spleen scan with 99Tcm sulfur colloid was negative; but when repeated with a gamma-camera and shielded liver, a splenunculus was demonstrated. After splenunculectomy a rapid remission occurred, and the patient has been well for 13 months.     

Splenic angioma with thrombocytopenia

A case of splenectomy with thrombocytopenia but without hypersplenism is described. The etiology, proven by splenectomy, was a splenic angioma. The isotopic examinations necessary to localize the site of a vascular tumor and the relations between thrombocytopenia and hemangioma are discussed.