Vessel wal

Metabolic and Inflammatory Disorders Acute febrile illnesses may result in vascular damage. This can result from immune complexes containing viral antigens or the viruses themselves. Certain pathogens, such as the rickettsiae causing Rocky Mountain spotted fever, replicate in endothelial cells and damage them. Vascular purpura may occur in patients with polyclonal gammopathies but more commonly in those with monoclonal gammopathies, including Waldenstrom's macroglobulinemia, multiple myeloma, and cryoglobulinemia.

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von Willebrand Disease vWD is the most common inherited bleeding disorder. Estimates from laboratory data suggest a prevalence of approximately 1%, but data based on symptomatic individuals suggest that it is closer to 0.1% of the population. vWF serves two roles: (1) as the major adhesion molecule that tethers the platelet to the exposed subendothelium; and (2) as the binding protein for FVIII, resulting in significant prolongation of the FVIII half-life in circulation.

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Patients with type 2 vWD have functional defects; thus, the vWF antigen measurement is significantly higher than the test of function. For types 2A, 2B, and 2M, vWF activity is decreased, measured as ristocetin cofactor or collagen binding activity. In type 2A vWD, the impaired function is due either to increased susceptibility to cleavage by ADAMTS13, resulting in loss of intermediate- and high-molecular weight (M.W.) multimers, or to decreased secretion of these multimers by the cell.

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Thrombotic Thrombocytopenic Purpura TTP and HUS were previously considered overlap syndromes. However, in the past few years the pathophysiology of inherited and idiopathic TTP has become better understood and clearly differs from HUS. TTP was first described in 1924 by Eli Moschcowitz and characterized by a pentad of findings that include microangiopathic hemolytic anemia, thrombocytopenia, renal failure, neurologic findings, and fever. The full-blown syndrome is less commonly seen now, probably due to earlier diagnosis.

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Hemolytic Uremic Syndrome HUS is a syndrome characterized by acute renal failure, microangiopathic hemolytic anemia, and thrombocytopenia. It is seen predominantly in children and in most cases is preceded by an episode of diarrhea, often hemorrhagic in nature. Escherichia coli O157:H7 is the most frequent, although not only, etiologic serotype. HUS not associated with diarrhea (termed DHUS) is more heterogeneous in presentation and course.

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Laboratory Testing for HIT HIT (antiheparin/PF4) antibodies can be detected using two types of assays. The most widely available is an enzyme-linked immunoassay (ELISA) with PF4/polyanion complex as the antigen. Since many patients develop antibodies but do not develop clinical HIT, the test has a low specificity for the diagnosis of HIT. This is especially true in patients who have undergone cardiopulmonary bypass surgery, where approximately 50% of patients develop these antibodies postoperatively.

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Immune Thrombocytopenic Purpura: Treatment The treatment of ITP utilizes drugs that decrease reticuloendothelial uptake of the antibody-bound platelet and/or decrease antibody production. However, the diagnosis of ITP does not necessarily mean that treatment must be instituted. Patients with platelet counts 30,000/µL appear not to have increased mortality related to the thrombocytopenia.

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Table 109-1 Drugs Definitively Reported to Cause Isolated Thrombocytopeniaa Abciximab Digoxin Acetaminophen Eptifibatide Acyclovir Hydrochlorothiazide Aminosalicylic acid Ibuprofen Amiodarone Levamisole Amphotericin B Octreotide Ampillicin Phenytoin Carbamazepine Quinine Chlorpropamide Rifampin Danazol Tamoxifen Diatrizoate meglumine (Hypaque Meglumine) Tirofiban Trimethoprim/sulfamethoxazole Diclofenac Vancomycin a Drugs that preceded thrombocytopenia and full recovery occurred after drug discontinuation, but recurred with re-introduction of the drug, and ot...

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Thrombocytopenia Thrombocytopenia results from one or more of three processes: (1) decreased bone marrow production; (2) sequestration, usually in an enlarged spleen; and/or (3) increased platelet destruction. Disorders of production may be either inherited or acquired. In evaluating a patient with thrombocytopenia, a key step is to review the peripheral blood smear and to first rule out "pseudothrombocytopenia," particularly in a patient without an apparent cause for the thrombocytopenia. Pseudothrombocytopenia (Fig.

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Approach to the Patient: Thrombocytopenia The history and physical examination, results of the CBC, and review of the peripheral blood smear are all critical components in the initial evaluation of the thrombocytopenic patients (Fig. 109-2). The overall health of the patient and whether he/she is receiving drug treatment will influence the differential diagnosis. A healthy young adult with thrombocytopenia will have a much more limited differential diagnosis than an ill hospitalized patient who is receiving multiple medications.

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Harrison's Internal Medicine Chapter 109. Disorders of Platelets and Vessel Wall Disorders of Platelets and Vessel Wall: Introduction Hemostasis is a dynamic process in which the platelet and the blood vessel wall play key roles. Platelets become activated upon adhesion to von Willebrand factor (vWF) and collagen in the exposed subendothelium after injury. Platelet activation is also mediated through shear forces imposed by blood flow itself, particularly in areas where the vessel wall is diseased, and is also affected by the inflammatory state of the endothelium.

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