Megaloblastic Anemias

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Chapter 7

• Megaloblastic Anemias

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1. Study Questions2. Homework Assignment3.
Exam for Unit III
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Morphology of Human Blood and Marrow Cells

• In Chapter 7, you will learn about megaloblastic
  anemias.  You will study Vitamin B12 deficiency
  and Folic Acid deficiency anemias.  The Schilling
  test for pernicious anemia is discussed. 
  Treatments for each type of anemia are covered. 
  Other non-megaloblastic, but macrocytic, anemias
  are discussed.

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Megaloblastic Anemias

• Group of disorders characterized by defective
  nuclear maturation caused by impaired DNA
  synthesis.
• Manifested by presence of large and abnormal red
  cell precursors (megaloblastic) in bone marrow
  and macro-ovalocytes in peripheral blood, also
  see giant granulocyte precursor.

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Biochemical Aspect

• Defective nuclear maturation and megaloblastic
  morphology caused by decrease in thymidine
  triphosphate (TTP) synthesis from uridine
  monophosphate (UMP). Defect interferes with
  nuclear maturation, DNA replication, and cell
  division.
• Primary causes for lack of thymidine and,
  consequently, defective DNA synthesis, are
  Vitamin B12 and folic acid deficiencies. Some
  drugs interfere with metabolism of these vitamins.

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Clinical Manifestations of Megaloblastic Anemias

• Degree of anemia ranges from mild to severe with
  symptoms of weakness, fatigue, shortness of
  breath and light-headedness. Congestive heart
  failure may/may not be present.
• In severe anemia, may have lemon yellow skin tint
  because of mild jaundice and pallor. May see an
  increase in bilirubin. 

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Ineffective Hematopoiesis 1 of 2

• Megaloblastic anemia associated with ineffective
  erythropoiesis and hemolysis.
• MCV gt 100 fL and as high as 160 fL. MCV reflects
  megaloblastic picture of bone marrow.
• Increased erythrocyte precursors in bone marrow
  and decreased release into peripheral blood
  indicate ineffective erythropoiesis See
  decrease in reticulocytes.

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Ineffective Hematopoiesis 2 of 2

• Megaloblastic RBCs have shortened life span.
  Evidence of intramedullary hemolysis includes
  increased bilirubin, LDH (LDH1 LDH2), serum
  iron, slight ? TIBC.
• Ineffective granulopoiesis defined by increased
  bone marrow leukocyte precursors and failure to
  release mature forms into peripheral blood.
• Ineffective thrombopoiesis shown by presence of
  increased abnormal platelets in bone marrow and
  thrombocytopenia in peripheral blood.

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Bone Marrow Morphology

• Have hypercellular bone marrow.  
• Nuclear to cytoplasm asynchrony Nucleus and
  cytoplasm mature at different rates.

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Peripheral Blood Morphology 1 of 3

• Macrocytic, normochromic anemia.  MCV may range
  from 100-160 fL.  MCH is elevated but MCHC is
  normal. Do NOT call megaloblastic anemia on
  basis of indices alone.
• Hemoglobin may be low to normal.  RBC count
  usually decreased.  Leukocyte count begins as
  normal, but decreases as anemia progresses.
  Platelets also slowly decrease.
• Peripheral smear hypocellular with presence of
  macrocytes and macro-ovalocytes. Degree of aniso
  and poik vary depending on severity of anemia.

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Peripheral Blood Morphology 2 of 3

• Poikilocytosis includes schistocytes, teardrops,
  spherocytes and target cells.
• RDW is increased. May see dimorphic RBC
  populations if have iron deficiency and
  megaloblastic anemias together.
• Red cell inclusions include Howell-Jolly bodies,
  basophilic stippling, and Cabot rings.
• May see NRBCs.  Will have decreased reticulocyte
  count.

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Peripheral Blood Morphology 3 of 3

• In patients with megaloblastic anemia, life span
  of RBC is 27-75 days. Survival time of normal
  RBCs transfused to patient with untreated
  megaloblastic anemia is shortened, cause is
  unknown.
• Hypersegmented neutrophils or multilobed
  neutrophils seen in peripheral blood. Have more
  than 5 lobes.  Are larger in size. Usually
  reported as present should give a percent value.
• Diagnosis usually based on morphology seen on
  peripheral blood smear and other biochemical
  tests. Usually do not do bone marrow.

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Etiologies

• Major causes are Vitamin B12 deficiency, folic
  acid deficiency or combination of both. Can be
  in myelodysplastic syndrome, acute leukemias.
  May be drug-induced (anticonvulsants or
  chemotherapeutic drugs)

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Vitamin B12 Deficiency Anemia
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Sources and Requirements

• Vitamin B12 produced by micro-organisms and
  fungi. Present in liver, fish, poultry, meat,
  eggs and dairy products. Vegetables do not
  contribute B12 to diet. Supplements available.
• Vitamin B12 requirements increase during
  pregnancy, infancy, during growth and during
  increased metabolic states. Body stores B12 in
  liver. B12 lost through feces and urine.
• Because the daily requirement of vitamin B12 is
  low and the storage rate is high, it takes 2-7
  years to develop Vitamin B12 deficiency as a
  result of malabsorption.

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Transport and Metabolism

• Two important proteins are involved in the
  transport of vitamin B12 from the duodenum to the
  ileum and from the ileum to the tissues the
  intrinsic factor (IF) and transcobalamin II

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Causes of Vitamin B12 Deficiency

• Deficiency progresses through four stages 
• Stage I - negative Vitamin B12 balance
• Stage II - B12 depletion
• Stage III - B12 deficient erythropoiesis
• Stage IV - B12 deficient anemia

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Dietary Vitamin B12 Deficiency 1 of 2

• Nutritional Vitamin B12 deficiency uncommon in
  western countries and is limited to vegetarians.
  Have an increase in plasma folate level with
  decrease in vitamin B12.
• Newborns with B12 deficient or depleted
  B12 mothers are born B12 deficient, especially if
  breastfed. If untreated, will develop
  megaloblastic anemia. Show retarded growth and
  psychomotor development. Also have neurologic
  complications.

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Dietary Vitamin B12 Deficiency 2 of 2

• The major cause of vitamin B12 deficiency is
  malabsorption.
• The most common form of malabsorption is
  pernicious anemia.
• Other causes of vitamin B12 deficiency include
  gastrectomy, fish tapeworm, disease of ileum or
  pancreas, and drugs such as alcohol.

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Pernicious Anemia (PA) 1 of 2

• Most common cause of vitamin B12 deficiency.
• Chronic disease caused by the deficiency of IF.
• Lack of IF leads to poor B12 absorption, and,
  consequently, megaloblastic anemia.
• Disease characterized by gastric parietal cell
  atrophy. Causes decreased secretion of intrinsic
  factor and other gastric juices.

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Pernicious Anemia (PA) 2 of 2

• More common in people of Scandinavian, English
  and Irish descent. More common after age 50. Is
  rare in children (congenital form).
• Congenital pernicious anemia characterized by
  total absence of IF and normal secretion of other
  gastric juices.  Are no antibodies against IF or
  the parietal cells.

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Pathophysiology of PA

• Main cause PA is atrophic gastritis characterized
  by atrophy of gastric mucosa with decrease of
  gastric secretions and IF.
• The cause of gastric atrophy is probably
  autoimmune.
• IF is essential for absorption of vitamin B12.
• In the absence of IF, only a small amount of
  vitamin B12 is absorbed, causing a gradual
  deficiency in vitamin B12.

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Genetic Factors of PA

• The congenital form of PA is inherited as an
  autosomal-recessive trait and is primarily seen
  in children before age two.

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Immunologic Factors of PA

• Serum of patients with PA contains autoantibodies
  to parietal cells, to IF, and to thyroid tissue.
  
• Have seen association between PA and other
  autoimmune diseases.

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Clinical Manifestations of Vitamin B12 Deficiency

• Onset usually very gradual. Have all signs and
  symptoms of any megaloblastic anemia.
• Fever usually present in severe anemia
• Loss of appetite
• Weakness
• Glossitis (sore tongue or beefy red tongue)
• Paresthesias
• Bone marrow megaloblastic and see
  macro-ovalocytes in peripheral blood.
• Associated with gastrointestinal, thrombotic,
  psychiatric, and neurologic complications

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Neurologic Manifestations of Vitamin B12
Deficiency

• Neurologic problems are more common in pernicious
  anemia than in other types of vitamin B12
  deficiencies.
• Degree of neurologic involvement not related to
  severity of anemia. May be mild, moderate or
  severe. May involve degeneration of peripheral
  nerves and spinal cord.
• In early stages, feel tingling pins and needles
  in toes and later in all four limbs, clumsiness,
  and have trouble walking.
• Later stages involve severe weakness and
  stiffness of limbs, impairment of memory and
  depression. Severe psychiatric symptoms are
  referred to as megaloblastic madness.
• In untreated patients, the neurologic symptoms
  are progressive.

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Other Causes of Vitamin B12 Deficiency

• Other causes of vitamin B12 deficiency include
• Gastrectomy, where the IF-producing cells are
  removed.
• Blind loop syndrome, an anatomic abnormality of
  small intestine.  Have overgrowth of bacteria in
  small bowel and the bacteria absorb all Vitamin
  B12 that is available. Corrected by giving
  tetracycline.
• Fish tapeworm, a parasite that competes with
  vitamin B12.
• Disease of ileum or pancreas.
• Drugs such as alcohol.

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Folic Acid Deficiency Anemia
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Sources and Requirements of Folic Acid 1 of 2

• Folic acid, also called folate, folacin or
  pteroylglutamic acid. Is water soluble vitamin.
  Concentrated in green leafy vegetables, fruits,
  dairy products, cereals, and in animal foods such
  as liver and kidney.
• Recommended daily requirement is about 50-100 µg
  per day. Requirement dramatically increases
  during infancy, pregnancy and lactation.

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Sources and Requirements of Folic Acid 2 of 2

• Folate deficiency during early pregnancy can have
  adverse effects on fetus, including paralysis and
  brain damage.
• Stored mainly in liver. Some stored in bone
  marrow and kidneys. Absorbed through duodenum
  and jejunum. Folate lost via body secretions
  such as bile, urine, sweat and saliva.
• Takes only a few months to develop folate
  deficiency.

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Structure of Folic Acid

• Made of three components pteridine,
  para-aminobenzoic acid and glutamic acid.
• Folic acid derived from diet not biologically
  active. Once absorbed, is hydrolyzed, reduced,
  and methylated to form biologically active forms.
  
• Serum folate is in form methyltetrahydrofolate
  and enters all tissue cells in this form
  (CH3THF).
• Vitamin B12 is required for folate to enter cells.

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Causes of Folic Acid Deficiency 1 of 3

• Main cause is dietary deficiency.  Other causes
  include malabsorption, increased requirement and
  drug-induced folate deficiencies.
• Nutritional deficiency usually consequence of
  poverty, old age, alcoholism and chronic
  diseases.
• Most common causes of folate malabsorption are
  tropical sprue and gluten-sensitive enteropathy.

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Causes of Folic Acid Deficiency 2 of 3

• Tropical sprue is infection that causes
  intestinal atrophy with clinical manifestations
  of weakness, weight loss and steatorrhea.
  Affects entire intestine and, therefore, causes
  wide variety of nutritional deficiencies,
  including Vitamin B12.  Treatment is antibiotic
  therapy.
• Gluten-sensitive enteropathy has same clinical
  manifestations as tropical sprue. Includes both
  non-tropical sprue and childhood celiac disease.
  Affected patients cannot digest gluten, protein
  found in wheat and other grains. Severe lesions
  develop in proximal intestine.

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Causes of Folic Acid Deficiency 3 of 3

• Childhood celiac disease is malabsorption
  syndrome resulting in anemia caused by iron
  deficiency and to lesser degree by Vitamin B12
  and folate deficiencies.
• Requirement for folate increases during rapid
  cellular proliferation (sickle cell anemia,
  thalassemia, spherocytosis or autoimmune
  hemolytic anemia).
• Drug induced folate-deficient megaloblastic
  anemias been reported. Drugs include
  methotrexate, phenytoin, alcohol, oral
  contraceptives, and the antimalarial drug
  -pyrimethamine.

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Clinical Manifestations of Folic Acid Deficiency

• Same as those for Vitamin B12 deficiency.
• Onset is insidious.
• Peripheral blood and bone marrow morphology same
  as Vitamin B12 deficiency.
• Rare to see neurologic or psychological
  abnormalities.

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Laboratory Diagnosis and Treatment
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Laboratory Diagnosis of Megaloblastic Anemia

• Must consider patients physical examination,
  medical history, family history and laboratory
  tests.
• Laboratory screening tests include Low
  hemoglobin and hematocrit, elevated MCV,
  peripheral smear evaluation (macro-ovalocytes and
  hypersegmented neutrophils).
• Must determine exact causes of megaloblastic
  anemia.

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Differential Diagnosis of Vitamin B12 and Folic
Acid Deficiencies

• Figure 7-15, page 123

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Laboratory Diagnosis of Megaloblastic Anemia
cont

• Other tests that may support specific diagnosis
  are 
• Antibodies to IF - present in about 50 of cases.
  Is specific for diagnosis of PA.
• Schilling test - evaluates absorption of
  Cobalt-labeled Vitamin B12 from intestinal tract.
  Is  specific for B12. Is done to pinpoint cause
  of B12 malabsorption.

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Treatment for Vitamin B12 Deficiency

• Most people with a vitamin B12 deficiency require
  lifelong vitamin therapy.  Cyanocobalamin and
  hydroxocobalamin are the two therapeutic forms of
  vitamin B12 available.
• B12 orally, injected intramuscularly or
  sub-cutaneously.

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Treatment for Folic Acid Deficiency

• Folic acid given daily over 2-3 week period. Is
  given orally. Life-long therapy usually not
  required.
• May be given along with B12.

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Response to Therapy

• Initial sign is dramatic increase in reticulocyte
  count. May increase 50-70 initially, 5-8 days
  after beginning therapy.
• Megaloblastic morphology of bone marrow
  disappears within first 48 hours.
• Hematocrit returns to normal in 4-8 weeks.
• Giant metamyelocytes and hypersegmented
  neutrophils disappear within 2 weeks.
• Bilirubin returns to normal after 3-4 weeks.

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Vitamin Independent Megaloblastic Changes
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Vitamin Independent Megaloblastic Changes

• Megaloblastic changes in peripheral blood and
  bone marrow not always caused by vitamin
  deficiency. May occur because of inherited or
  acquired predisposition, or may be drug-induced.
• Orotic aciduria rare inherited disorder of
  pyrimidine metabolism.
• Lesch-Nyhan syndrome X-linked disorder of purine
  metabolism.
• Toxic materials such as arsenic can also cause
  megaloblastic anemia.

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Macrocytic, Nonmegaloblastic Anemias
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Macrocytic Nonmegaloblastic Anemias

• Macrocytic anemias may be megaloblastic or
  nonmegaloblastic Must differentiate between
  them.
• In macrocytic, normoblastic anemias, MCV is
  usually 100-110 fL In macrocytic, megaloblastic
  anemias, MCV is usually gt 110 fL.
• Macrocytic normoblastic erythrocytes are large
  and round - not oval, and no hypersegmented
  neutrophils are present Megaloblastic RBCs are
  often ovalocytes, and hypersegmented neutrophils
  are present.
• Exact mechanism macrocytic normoblastic anemias
  unknown. May be due to change in lipid content
  on red cell membrane or to altered maturation
  time of red cell precursors.
• Most common causes of macrocytic nonmegaloblastic
  anemias are chronic liver disease and alcoholism.
  In most alcoholics, macrocytosis is present
  without anemia.