Macrocytic Anaemia Past Paper 2008 PDF

PRESENTER DR J. N. OLIWA FACILITATOR DR. F. ABDALLAH 18/03/2008  Introduction-definitions and classification of anaemia  Macrocytic anaemia-megaloblastic vs. nonmegaloblastic  Metabolism of Vitamin B12 & Folate  Deficiencies of Vitamin B12 & Folate  Pathophysiology & clinical...

PRESENTER DR J. N. OLIWA FACILITATOR DR. F. ABDALLAH 18/03/2008  Introduction-definitions and classification of anaemia  Macrocytic anaemia-megaloblastic vs. nonmegaloblastic  Metabolism of Vitamin B12 & Folate  Deficiencies of Vitamin B12 & Folate  Pathophysiology & clinical features  Diagnosis & Lab. Features  Management  Summary  Introduction Anemia or anæmia/anaemia from the Greek (Ἀναιμία) (an-haîma) meaning "without blood", is defined as a qualitative or quantitative deficiency of hemoglobin, a molecule inside red blood cells (RBCs). Anaemia is functionally defined as an insufficient erythrocyte mass to adequately deliver oxygen to peripheral tissues, leading to hypoxia (lack of oxygen) in organs. The three main classes of anemia include excessive blood loss (acutely such as a hemorrhage or chronically through low-volume loss), excessive blood cell destruction (hemolysis)  Macrocytosis is a term used to describe erythrocytes that are larger than normal, typically reported as mean cell volume (MCV) greater than 95 fL. The amount of hemoglobin in the cell increases proportionately, so the mean cell hemoglobin concentration (MCHC) remains within normal limits.  The most common cause of macrocytic anemia is megaloblastic anemia, which is the result of impaired DNA synthesis.  Nonmegaloblastic macrocytic anemias are those in which no impairment of DNA synthesis occurs.  Are disorders caused by impaired DNA synthesis and are characterised by the presence of megaloblastic cells (larger than normal with nuclear cytoplasmic asynchrony).  This thought to be due to faster synthesis of cytoplasmic constituents (RNA&proteins) compared to DNA leading to delayed maturation of the nucleus.  Underlying defect is deficiency of either folate or cobalamin (Vit B12). Folate is needed for the conversion of deoxyuridine monophosphate (dUMP) to deoxthymidine monophosphate (dTMP)  Cobalamin is needed to convert 5methyl tetrahydrofolate to its active form THF and in the process Homocysteine to Methionine. Are those in which no impairment of DNA synthesis occurs. Causes include :-*  Alcohol Hypopituitarism  Liver disease Scurvy  Hypothyroidism PEM  Reticulocytosis  Aplastic anaemia  Red cell aplasia  Myelodysplasia  Cytotoxic drugs Paraproteinaemia (such as myeloma)  Pregnancy  Neonatal period * These are usually associated with a normoblastic marrow  Vitamin B12 is an essential water-soluble vitamin, member of the vitamin B complex. It contains cobalt. It is exclusively synthesised by bacteria and is found primarily in meat, eggs and dairy products. B12 is the most chemically complex of all the vitamins.  The DRI for vitamin B12 is 2.4 micrograms for adults. Amounts listed on a nutrition label are based on 6 µg/day. For example, 25% of the Daily Value =.25 * 6 µg = 1.5 µg. There has been considerable research into possible plant food sources of B12. Fermented soya products, seaweeds, and algae such as spirulina have all been suggested as containing significant B12. However, the present consensus is that any B12 present in plant foods is likely to be unavailable to humans and so these foods should not be relied upon as safe sources.  Protein-bound vitamin B12 is released in the stomach's acid environment and is bound to R protein (haptocorrin). Pancreatic enzymes cleave this B12 complex (B12-R protein) in the small intestine. After cleavage, intrinsic factor, secreted by parietal cells in the gastric mucosa, binds with vitamin B12. Intrinsic factor is required for absorption of vitamin B12, which takes place in the terminal ileum.  Vitamin B12 in plasma is bound to transcobalamins I and II. Transcobalamin II is responsible for delivering vitamin B12 to tissues. The liver stores large amounts of vitamin B12.  Enterohepatic reabsorption helps retain vitamin B12. Liver vitamin B12 stores can normally sustain physiologic needs for 3 to 5 yr if B12 intake stops (eg, in people who become vegans) and for months to 1 yr if enterohepatic reabsorption capacity is absent. Causes of Vitamin B12 Deficiency Cause Source Inadequate diet Vegan diet Breastfeeding of infants by vegan mothers Fad diets Impaired absorption Lack of intrinsic factor (due to pernicious anemia, destruction of gastric mucosa, gastric surgery, or gastric bypass surgery) Intrinsic factor inhibition Decreased acid secretion Small-bowel disorders (eg, inflammatory bowel disease, sprue, cancer, biliary or pancreatic disorders) Competition for vitamin B12 (in fish tapeworm infestation or blind loop syndrome) AIDS Inadequate utilization Enzyme deficiencies Liver disorders Transport protein abnormality Drugs Antacids Metformin GLUCOPHAGE Nitrous oxide (repeated exposure)  Folic acid is composed of a pterin ring connected to p- aminobenzoic acid (PABA) and conjugated with one or more glutamate residues. It is distributed widely in green leafy vegetables, citrus fruits, and animal products. Humans do not generate folate endogenously because they cannot synthesize PABA, nor can they conjugate the first glutamate.  Folates are present in natural foods and tissues as polyglutamates because these forms serve to keep the folates within cells. In plasma and urine, they are found as monoglutamates because this is the only form that can be transported across membranes. Enzymes in the lumen of the small intestine convert the polyglutamate form to the monoglutamate form of the folate, which is absorbed in the proximal jejunum via both active and passive transport.  A healthy individual has about 500-20,000 mcg of folate in body stores. Humans need to absorb approximately 50-100 mcg of folate per day in order to replenish the daily degradation and loss through urine and bile. Otherwise, signs and symptoms of deficiency can manifest after 4 months.  The current standard of practice is that serum folate levels less than 3 ng/mL and a red blood cell (RBC) folate level less than 140 ng/mL puts an individual at high risk of folate deficiency. The RBC folate level generally indicates folate stored in the body, whereas the serum folate level tends to reflect acute changes in folate intake.  Leafy vegetables such as spinach, turnip greens, lettuces, dried beans and peas, fortified cereal products, sunflower seeds and certain other fruits and vegetables are rich sources of folate. Some breakfast cereals (ready-to-eat and others) are fortified with 25% to 100% of the recommended dietary allowance (RDA) for folic acid. 1. Inadequate ingestion of folate- containing foods  Poor nutrition is prevalent among people with alcoholism and patients with psychiatric morbidities, as well as elderly people (due to conditions such as ill-fitting dentures, physical disabilities, and social isolation).  Because folates are destroyed by prolonged exposure to heat, people of certain cultures that involve traditionally cooking food in kettles of boiling water may be predisposed to folate deficiency.  Moreover, for patients with renal and liver failure, anorexia and restriction of foods rich in protein, potassium, and phosphate contribute to decreased folate intake. 2. Impaired absorption  The limiting factor in folate absorption is its transport across the intestinal wall. Folate transport across the gut wall mainly is carrier mediated, saturable, substrate specific, pH dependent (optimal at low pH), sodium dependent, and susceptible to metabolic inhibitors. Passive, diffusional absorption also occurs, to a minor degree. With this in mind, a decreased absorptive area due to small bowel resection or mesenteric vascular insufficiency would decrease folate absorption.  Celiac disease and tropical sprue cause villous atrophy. The process of aging causes shorter and broader villi in 25% of the elderly population. Achlorhydria leads to elevation of gastric pH above the optimal level (ie, pH of 5) for folate absorption.  Anticonvulsant drugs, such as Dilantin, interfere with mucosal conjugase, hence impairing folate absorption.  Zinc deficiency also decreases folate absorption because zinc is required to activate mucosal conjugase.  Bacterial overgrowth in blind loops, stricture formation, or jejunal diverticula likewise would decrease folate absorption. 3. Impaired metabolism  This leads to inability to utilize absorbed folate: Antimetabolites that are structurally analogous to the folate molecule can competitively antagonize folate utilization. Methotrexate and trimethoprim both are folate antagonists that inhibit dihydrofolate reductase.  Hypothyroidism has been known to decrease hepatic levels of dihydrofolate reductase as well as methylene THFA reductase.  Furthermore, congenital deficiency involving the enzymes of folate metabolism also can show impaired folate utilization.  People with alcoholism can have very active alcohol dehydrogenase that binds up folate and thus interferes with folate with folate utilization. 4. Increased requirement Factors that increase the metabolic rate can increase the folic requirement:-  Infancy (a period of rapid growth)  Pregnancy (rapid fetal growth)  Lactation (uptake of folate into breast milk)  Malignancy (increased cell turnover)  Concurrent infection (immunoproliferative response)  Chronic hemolytic anemia (increased hematopoiesis) all can result in an increased folate requirement. 5. Increased excretion/loss  Increased excretion of folate can occur subsequent to vitamin B-12 deficiency. During the course of vitamin B-12 deficiency, methylene THFA is known to accumulate in the serum, which is known as the folate trap phenomenon.  In turn, large amounts of folate filter through the glomerulus, and urine excretion occurs.  Another mechanism of excess excretion occurs in people with chronic alcoholism who can have increased excretion of folate into the bile.  Patients undergoing hemodialysis also have been known to have excess folate loss during procedures. 6. Increased destruction  Superoxide, an active metabolite of ethanol metabolism, is known to inactivate folate by splitting the folate molecule in half between the C9 and N10 position.  The relationship between cigarette smoking and low folate levels has been noted as possibly due to folate inactivation in exposed tissue.  Symptoms are attributable to the underlying condition causing the anemia or directly to the anemia.  Because the anaemia dvps slowly, it produces few symptoms until the hct is severely depressed. Symptoms may incl. weakness, palpitations, fatigue, lightheadedness, and shortness of breath.  Lemon-yellow skin colouration is due to the pallor and mild jaundice due to incr. breakdown of Hb due to ineffective erythropoiesis.  The thrombocytopenia occas. leads to easy bruising (aggravated by vit C def)  Anaemia and reduced leucocyte count predispose to infections. Cobalamin def. has also been assoc’d with impaired bactericidal function of macrophages.  Glossitis, angular stomatitis and mild malabsorption are due to the abnormalities of epithelial cells.  Epithel.surf. of the mouth, stomach, small intestines, resp, urinary and female genital tracts are affected. The cells show macrocytosis, increased numbers of multinucleate dying cells (may be confused for atypia).  The gonads are affected and infertility is common.  Maternal folate def. has been implicated as a cause of prematurity and recurrent foetal loss.  NTDs(anaenceph, encephalocoeles, memingomyelocoeles, occulta) and incidence of cleftlip&palate are also assoc’d with maternal folate def. As (Relationship is unclear, but is inverse) Demyelination of the cord Severe NTDs Glossitis 1. Complete CBC with platelet count  The hemoglobin/hematocrit level may provide a guide to diagnosis, and it determines presence and severity of anemia.  WBC and platelet count may be decreased in primary marrow disturbances.  The MCV is a calculated average volume of the erythrocytes. An MCV greater than 100 fL is, by definition, macrocytosis. Because evaluation of the RBC size is key to the diagnosis of an anemia, the MCV is considered to be the most important of the RBC indices. 2. Peripheral blood smear morphology may be helpful. Round macrocytes suggest liver or marrow infiltrative disease, whereas oval macrocytes tend to suggest a megaloblastic disorder.  This study provides clues to the etiology of macrocytosis.  Hypersegmented neutrophils and macro-ovalocytes strongly suggest megaloblastic anemia.  Nucleated RBCs, teardrop cells, decreased and/or large platelets, and immature WBCs are often present in myelophthisic disease and leukemias. 3. Reticulocyte count  This study helps to determine if hemolysis is present; it also indicates malfunctioning bone marrow.  Expect marked reticulocytosis (>4) in hemolytic anemias.  Reticulocyte count less than 1% indicates inadequate marrow production.  Reticulocyte count must be corrected for degree of anemia.  Bone marrow aspirate (and biopsy) -The bone marrow biopsy and aspirate determines if the marrow is functioning adequately and also may reveal replacement of marrow with tumor, granuloma, or fibrosis. Obtain the bone marrow prior to vitamin B-12 folate therapy or blood transfusion because megaloblastic changes may reverse rapidly. -The bone marrow in megaloblastic anemias is usually hypercellular with all cell lines proliferating. Marked erythroid hyperplasia may occur to the point at which the myeloid- erythroid ratio is reversed. Nuclear-chromatin dissociation with a young-appearing nucleus with abundant mature-appearing cytoplasm may occur(nuclear-cytoplasmic asynchrony) Granulocytic hyperplasia with giant metamyelocytes and bands often are noted. Histologic Findings  Blood: On peripheral smear, large RBCs are evident. Depending on the etiology of the macrocytosis, peripheral smear may reveal nucleated RBCs, target cells, RBC fragments, hypersegmentation of neutrophils, immature WBCs, large platelets, or pancytopenia (indicates severe disease)  Marrow: Depending on the etiology of the macrocytosis, marrow may reveal hypercellularity, megaloblastic changes, fibrosis, infiltration by tumor or granulomatous disease, leukemic changes, or erythroid hyperplasia. 4. Coombs test  Perform this test if the reticulocyte count is elevated to aid in confirming the diagnosis of hemolysis.  Expect a positive direct Coombs test finding in autoimmune hemolytic anemias, hemolytic transfusion reactions, and some drug-induced anemias (eg, penicillin, methyldopa, some cephalosporins, sulfonamides). 5. Lactate dehydrogenase (LDH) is elevated in both intravascular and extravascular hemolysis including the ineffective erythropoiesis that occurs in megaloblastic anemias. 6. Because the haptoglobin binds free hemoglobin, a low or absent haptoglobin level indicates intravascular hemolysis. 7. If macro-ovalocytes and hypersegmented neutrophils are noted on peripheral smear, the vitamin B-12 level may be low. 8. RBC folate levels  If folate deficiency is the cause of the macrocytosis, the RBC folate level likely will be decreased.  As in vitamin B-12 deficiency, peripheral smear may reveal hypersegmented neutrophils and macro-ovalocytes. 9. Homocysteine level: Serum total homocysteine levels almost always are elevated in patients with folate deficiency, because folate is required in the remethylation step converting homocysteine to methionine. Serum methylmalonic acid and homocysteine levels may be increased even in early vitamin B-12 deficiency. 10. Serum unconjugated bilirubin is expected to be elevated in hemolysis. Normal PBF PBF-Macro-ovalocytes PBF: Hypersegmented neutrophils Anisopoikilocytosis, hypersegmented neutrophils Hypersegmented neutrophil, macro-ovalocytes Macrocytes, hpersegmented neutrophil Megaloblastic bonemarrow BM -Medical treatment depends on the etiology of the macrocytosis, the presence and severity of an anemia, and the symptoms of the patient.  After the appropriate laboratory studies are obtained, the symptomatic anemic patient may be transfused with packed RBCs.  If a drug is thought to be the cause of the macrocytic anemia, especially if hemolysis is occurring, discontinue administration of the offending drug.  Patients deficient in vitamin B-12 or folate should receive replacement therapy.  Counsel patients suspected of abusing alcohol to abstain.  Treat malignancies, granulomatous diseases, and COPD according to standards for each. -Hospitalization may be required to treat some causes of macrocytosis, especially acute leukemias. -Consultations with the Hematology & Oncology teams. Diet  If folate or vitamin B-12 deficiency is the cause of the macrocytosis, modify the diet to include foods rich in these vitamins. Red meat is a good source of vitamin B-12, and green leafy vegetables are excellent sources of folate. Do not provide folate supplementation without vitamin B-12 replacement therapy in any patient with vitamin B-12 deficiency or with suspected vitamin B-12 deficiency, since this may precipitate subacute combined degeneration of the spinal cord.  The treatment for vitamin B12-deficient anemia was first devised by William Murphy who bled dogs to make them anemic and then fed them various substances to see what (if anything) would make them healthy again. He discovered that ingesting large amounts of liver seemed to cure the disease.  George Minot and George Whipple then set about to chemically isolate the curative substance and ultimately were able to isolate the vitamin B12 from the liver. All three shared the 1934 Nobel Prize in Medicine. Questions?? Thank You For Your Attention..