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Lecture 13
Hemolytic Anemia II
| Question | Answer |
|---|---|
| Microscopic findings characteristic of thrombotic microangiopathy | (1)Vessel wall thickening of arterioles and capillaries (2)Swelling or detachment of endothelial cells from basement membrane (3)Material accumulation in the subendothelial space (4)Intraluminal thrombosis |
| Syndrome of thrombotic microangiopathy, thrombocytopenia, neurologic deficits, fever, and mild renal dysfunction. | Thrombotic Thrombocytopenic Purpura |
| A syndrome of thrombotic microaniopathy and severe renal dysfunction associated with E. coli O157:H7 infection. | Hemolytic Uremic Syndrome |
| Classic pentad of symptoms of Thrombotic Thrombocytopenic Purpura | (1) Microangiopathic hemolysis (2) Thrombocytopenia (Platelets <80,000 with normal PT and PTT) (3) Neurologic deficits (4) Fever (5) Renal Dysfunction |
| What is the most common cause of renal failure in children? | Shiga toxin induced Hemolytic Uremic Syndrome |
| Pathophysiology of hemolytic uremic syndrome | Diffuse endothelial damage caused by toxins (eg Shiga toxin) that in turn trigger caogulation and formation of thrombi. Increased shear stress around thrombi cause fragmentation of red cells. |
| What are the predisposing factors for renal failure in Shiga-toxin induced Hemolytic Uremic Syndrome? | (1) WBC > 13,000 (2) Treatment with anti-motility agents (3) Treatment with antibiotics (4) Genetic factors |
| Pathophysiology of renal failure caused by Shiga toxin | Shiga toxin released by bacteria is carried to the renal endothelium by leukocytes. Renal endothelial cells internalize toxins via glycosphinolipid on cells membrane. Toxin induce changes in endothelium to a procaoagulant state, promoting thrombosis. |
| Pathophysiology of Thrombotic Thrombocytopenic Purpura | Autoantibodies inhibit ADAMTS13 causing accumulation of unusually large von Willebrane multimers (UlvWF). Shear stress of circulation exposes platelet binding sites on UlvWF, causing large thrombi and obstruction of small vessels. |
| What is the metalloprotease present in plasma that cleave unusually large von Willebrane multimers (UlvWF)? | ADAMTS13 |
| What is the genetic syndrome associated with Thrombotic thrombocytopenic purpura? | Schulman-Upshaw Syndrome |
| What drugs have been associated with Thrombotic thrombocytopenic purpura and Hemolytic uremic syndrome? | Ticlopidine, Clpidogrel, Quinine, Mitomycin, Cyclosporin, and Pentostatin |
| What illness and conditions have been associated with Thrombotic thrombocytopenic purpura and Hemolytic uremic syndrome? | (1) HIV (2) Post bone marrow transplantation (3) Cancer (4) Pregnancy (5) Autoimmune disorders (6) Abnormal components of the complement pathways (factor H) |
| What is the mortality of Thrombotic thrombocytopenic purpura and Hemolytic uremic syndrome without treatment? | 100% |
| What is the first line of therapy for Thrombotic thrombocytopenic purpura and Hemolytic uremic syndrome? | Plasma exchange |
| (T or F) Platelets can be safely given in Thrombotic thrombocytopenic purpura and Hemolytic uremic syndrome. | False. Platelet transfusion is contraindicated because they may exacerbate the underlying condition and should be only given for life threatening bleeding. |
| What treatments for Thrombotic thrombocytopenic purpura and Hemolytic uremic syndrome can be added if plasma exchange fails? | Other therapies can be added - glucocorticoids, rituximab, vincristine, staph protein A columns, and splenectomy. |
| Type of hemolysis associated with cardiace hemolysis | Direct Coombs Test negative intravascular hemolysis |
| What is the most common cause of cardiac hemolysis? | Cardiac hemolysis largely occurs with prosthetic valves especially aortic valves and those with valvular leaks. |
| What inherited membrane abnormalities are associated with hemolysis? | (1) Hereditary spherocytosis (2) Hereditary Elliptocytosis (3) Hereditary pyropoikilocytosis (4) Hereditary stomatocytosis |
| What is the membrane defect in hereditary spherocytosis? | Decreased spectrin resulting in membrane loss, spherocyte formation and decreased deformability. |
| What is the membrane defect in hereditary elliptocytosis? | Defective formation of spectrin tetramers |
| What is the membrane defect in hereditary pyropoikilocytosis? | Defective formation of spectrin tetramers |
| What is the membrane defect in hereditary stomatocytosis? | Defect in Na permeability |
| What two RBC enzyme defects are associated with hemolytic anemia? | (1) G6PD deficiency (2) Pyruvate kinase Deficiency |
| What is the most abundant protein in the underlying protein lattice of RBC membrane? | Spectrin |
| Pathogenesis of Hereditary Spherocytosis | Decreased amount of spectrin in RBC membrane causing decreased attachment of protein lattice to lipid bilayer. This results in spherocyte formation, which are poorly deformable. Decrease in the amount of membrane results in increased osmotic fragility. |
| What is the most common hereditary hemolytic disorder in Caucasians? | Hereditary Spherocytosis |
| What hemolytic disorder is characterized by spherocytes on peripheral blood smear with negative Direct Coombs Test? | Hereditary Spherocytosis |
| What is the most common pattern of inheritance of hereditary spherocytosis? | Autosomal dominant inheritance |
| What is a confirmatory test for Hereditary Spherocytosis? | Osmotic fragility test. Spherocytes have increased osmotic fragility. |
| Pathogenesis of Hereditary Elliptocytosis | Defects in self assembly of spectrin, spectrin-ankyrin binding, protein 4.1, and glycophorin C. |
| What may cause aplastic crisis in a hereditary spherocytosis? | Parvovirus B19 infection |
| Treatment for symptomatic hereditary spherocytosis | Splenectomy |
| What is the inheritance pattern of Hereditary Elliptocytosis? | Autosomal dominant inheritance |
| Treatment for symptomatic Hereditary Elliptocytosis | Splenectomy. Most patients require no treatment. |
| Pathogenesis of Glucose-6-Phosphate Dehydrogenase Deficiency | Hydrogen peroxide accumulates due to inadequate glutathione. Oxidative damage to hemoglobin by excess hydrogen peroxide causes Heinz body formation. Hydrogen peroxide also damages RBC membrane. Both intravascular and extravascular hemolysis occur. |
| What is the inheritance pattern of Glucose-6-Phosphate Dehydrogenase Deficiency? | Sex-linked |
| What is the most common variant of Glucose-6-Phosphate Dehydrogenase Deficiency? | Type B. Almost all whites and 70% of blacks have this type of G6PD deficiency. |
| Favism | Ingestion of fava beans causing life-threatening hemolysis in G6PD deficiency. Found in people of Mediterranean ancestry. Enzyme activity is absent and minor oxidative stress causes life-threatening hemolysis. |
| What are Heinz bodies? | Aggregates of denatured HgB |
| Function of Embden-Meyerhof glycolytic pathway | Provides energy as ATP for (1) Na/K pump affecting osmotic/volume balance (2) Phosphorylation of spectrin which affects membrane deformability |
| Pathogenesis of Pyruvate Kinase Deficiency | Cannot produce adequate amounts of ATP via the Embden-Meyerhoff glycolytic pathway affecting stability and deformability of the RBC. |
| What is the inheritance pattern of Pyruvate Kinase Deficiency? | Autosomal recessive |
| Treatment of severe hemolysis due to Pyruvate Kinase Deficiency | Splenectomy |
| What tests are needed for diagnosis of Pyruvate Kinase Deficiency? | (1) Enzyme screening test (2) Fluorescent spot test (3) Reticulocyte count |
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