Monday, 12 December 2011

Megaloblastic Anaemia

Diagnosis
  • Many cases are seen that have a decreased serum B12 with a normal haematological profile and possibly normal clinical findings
  • Test for methylmalonic acid in the serum as an indicator of vitB12 deficiency
  • Test for homocysteine to check folate levels
Haematological Profile
  • Hb/RCC/Hct - Dec (due to Dec. DNA production)
  • MCV/MCH - Inc. (As precursors are megaloblastic)
  • MCHC - Normal
  • RDW - Inc. (Anisocytosis due to microcytes, normocytes and oval macrocytes)
  • Plt./WCC - Dec
  • Pancytopaenia with a normochromic, macrocytic anaemia
  • Intramedullary haemolysis due to ineffective erythropoiesis (reason for hypercellular BM)
  • Poikilocytosis - ++ (tear drops and schistocytes)
  • Anisocytosis - +++ (oval macrocytes)
  • Hypersegmented neutrophils ("Shift-to-the-Right" - seen in 91% of megaloblastic anaemias where >5% of Neutrophils/Eosinophils have 5/3 lobes - diagnostic with oval macrocytes)
      A "Shift-to-the-Left" indicates an Inc. in band form WBCs "Hypersegmented" refers to >5% nuclei with 6 (or more) lobes
  • Hypercellular bone marrow (M:E at 1:1 or reversed)
  • Erythron
    • Large cells with fine chromatin (Megaloblasts)
    • Nuclear(N)/Cytoplasmic(C) dissociation with N lagging C - normal cytoplasmic maturation
    • Multiple Howell-Jolly bodies (diagnostic if observed)
  • Leucon
    • Giant myelocytes and metamyelocytes
  • Thrombon
    • Often not obvious
  • The peripheral blood (PB) and bone marrow (BM) findings do not distinguish between a vitamin B12/cobalamin deficiency and a folic acid (folate) deficiency
Treatment
  • Shotgun therapy may be used where the causative agent is unclear
    • Folate, then vitB12 - attempts to make the patient well
  • Intramuscular hydroxy-cobalamin daily for a week (regime will depend on the cause of the anaemia)
  • Monitor the reticulocyte count (should return to normal in 2-3 weeks) and the Hb concentration (20-30g/L rise every week until normal)
  • If no response occurs, the diagnosis is incorrect
  • If a response occurs and then reaches a plateau, an iron deficiency is complicating RBC production
Causes of Vitamin B12 Deficiency
  • Reflected by:
    • Impaired DNA synthesis
    • Defective fatty acid degradation (excessive demyelination)
  • Administration of folate will correct the anaemia but will not reverse any neurological disease - approximately 5% show no other symptoms but neurological disorder
  • Symptoms include:
    • Anaemia
    • Diarrhoea/constipation
    • Glossitis (shiny tongue)
    • Sterility/Infertility
    • Numb, tingling fingers (paresthesia), wobbly gait and potential paralysis
    • "Megaloblastic madness" due to mental problems
  • Nutritional
    • Rare
  • Malabsorption
    • Gatsric Disease
      • Gastrectomy - usually preceeded by iron deficiency
      • Pernicious Anaemia (PA):
        • Juvenile or adult
        • Can be fatal
        • More common in females
        • Autoimmune disease whereby Ab to parietal cells leads to gastric atrophy (loss of epithelial cells and intrinsic factor (IF)) or an Ab that blocks the function of IF
        • Most frequent in Northern Europe, running in families

        • The vitB12 Journey.
          IF-Intrinsic Factor; Cbl-vitB12/ or Cobalamin; TC II-transcobalamin II)
        • Testing
          • Lack of gastric HCl is an indirect measure of lack of IF as it is due to atrophy of gastric cells
          • Look for IF Ab's (Blocking-prevents B12 binding to IF; Binding-prevents B12-IF complex binding to the ileum). 70% of PA sufferers have these Ab's
          • If negative (30%) do a Schilling Test.
            • Patient's vitB12 binding proteins are saturated by giving a large dose of unlabelled B12 intravenously
            • Absorption (via the ileum) of cobalamin is measured following ingestion of radioactively labelled B12.
            • In a normal system, more than 10% of the radioactive cobalamin will be excreted in the urine over 24hours.
            • If less than 10% is excreted, the patient is given cobalamin + IF. If the patient is suffering from PA, greater than 10% of the labelled cobalamin will appear in the urine within 24hours, otherwise the patient can be said to have an absorption problem.
            • Low results may occur in patient's with kidney problems
    • Terminal ileal disease
      • Ileal resections
      • Ulcerative colitis (may be autoimmune)
      • Tropical sprue (generalised malabsorption syndrome - seen in New Guinea)
    • Competitive parasites
      • Diphylobothrium latum
    • Pancreatic failure (enzymes from the pancreas are required to allow binding of IF to vitB12)
    • Drug induced
    • Bacterial overgrowth (competition for vitB12)
  • Increased Requirement for B12
    • Pregnancy
    • Infancy
    • Cancer
    • Haemolytic anaemia
    • Leukaemia
    • Exfoliative dermatitis
    • Multiple myeloma
  • Disorders of Transport and Storage
    Folic Acid Deficiency
  • Folate is obtained from leafy vegetables
  • Deficiency results in anaemia in approx. 20 weeks
  • Require 50-100ug/day
  • Serum folate assay can be variable and should be carried out with a RBC folate assay (which indicates folate levels at the time of production of the RBCs)
  • Polyglutamate folate is the most common form of folate in food. The broken down, monoglutamate is transported across the intestinal mucosa, mostly at the jejunum and is primarily stored in the liver (capacity of 5-10mg)
    Condition
    Serum B12 Assay
    RBC Folate Assay
    Pernicious Anaemia
    Low
    Decreased
    Alcoholism
    Normal
    Low
    Acute Folate Deficiency
    Normal
    Normal

  • Folate is taken into cells as N5-methyl-tetrahydrofolate(THF). This must be demethylated (which is mediated by cobalamin) before conjugation can occur. If N5-THF is not conjugated, it will leak out of the cell again.
  • If cobalamin is in short supply, demethylation is impaired
  • Normally, dUMP is entirely converted to dTMP. With decreased levels of folate, this conversion is limited and a build-up of dUMP occurs instead. As a consequence, dUTP concentration rises and begins to replace dTTP in DNA synthesis.
  • Error correction attempts to replace the U's but fails due to the lack of T's and DNA synthesis is interrupted
  • Note: Goat's milk is lower in folate than cow's milk

    Causes

  • Nutritional
    • An incomplete diet is the most common cause
    • Alcoholics
    • Elderly - overcooking destroys folate
  • Malabsorption
    • Tropical (general bowel disruption) and non-tropical (densitive to gluten - coeliac disease) sprue
    • Alcohol - interferes with absorption
    • Drug related - convulsive drugs, folate antagonists (eg. methotrexate-used for treatment of some neoplastic diseases), oral contraceptives
    • Anatomic and functional intestinal abnormalities
  • Increased Folate Requirement
    • Pregnancy
    • Infancy
    • Haemolytic anaemia
    • Acute leukaemia
    • Exfoliative dermatitis
    • Multiple myeloma
    • Metastatic cancer
    • Haemodialysis
  • Defective Utilization of Folate
  • Enzyme Deficiency
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