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Questions and Answers
What is a key biochemical role of vitamin B12 in DNA synthesis?
What is a key biochemical role of vitamin B12 in DNA synthesis?
Which of the following is NOT a characteristic of megaloblastic anaemia?
Which of the following is NOT a characteristic of megaloblastic anaemia?
What is the expected effect on plasma homocysteine levels in cases of vitamin B12 or folate deficiency?
What is the expected effect on plasma homocysteine levels in cases of vitamin B12 or folate deficiency?
Which cellular feature is specifically associated with megaloblastic anaemia?
Which cellular feature is specifically associated with megaloblastic anaemia?
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Which of the following neurological symptoms is commonly associated with vitamin B12 deficiency?
Which of the following neurological symptoms is commonly associated with vitamin B12 deficiency?
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In megaloblastic anaemia, which of the following is typically observed in the bone marrow?
In megaloblastic anaemia, which of the following is typically observed in the bone marrow?
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What percentage of patients with vitamin B12 deficiency may experience neurological diseases?
What percentage of patients with vitamin B12 deficiency may experience neurological diseases?
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Which symptom is most commonly reported by patients with megaloblastic anaemia?
Which symptom is most commonly reported by patients with megaloblastic anaemia?
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What is a characteristic sign of megaloblastic anemia?
What is a characteristic sign of megaloblastic anemia?
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Which of the following conditions can lead to vitamin B12 deficiency?
Which of the following conditions can lead to vitamin B12 deficiency?
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Which mechanism is essential for the absorption of vitamin B12?
Which mechanism is essential for the absorption of vitamin B12?
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What can rapid deficiency in body folate stores be attributed to?
What can rapid deficiency in body folate stores be attributed to?
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What is one potential cause for folate deficiency?
What is one potential cause for folate deficiency?
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Which test measures vitamin B12 absorption?
Which test measures vitamin B12 absorption?
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What type of anemia is characterized by megaloblastic bone marrow?
What type of anemia is characterized by megaloblastic bone marrow?
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What autoimmune disorder causes intrinsic factor deficiency?
What autoimmune disorder causes intrinsic factor deficiency?
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Study Notes
Megaloblastic Anaemia
- Definition: A type of anaemia caused by impaired DNA synthesis during red blood cell (RBC) production. It's due to deficiencies in vitamin B12 or folate, or issues in folate metabolism.
- Characteristics: High mean corpuscular volume (MCV) >110 fL, low hemoglobin (Hb) and RBC count, and decreased white blood cells (WBC) and platelets.
- Folate's Role: Crucial for DNA synthesis.
- Vitamin B12's Role: Acts as a co-factor in converting homocysteine to methionine, creating tetrahydrofolate needed for DNA synthesis.
- Consequences of Deficiencies: Elevated plasma homocysteine levels and impaired DNA synthesis, resulting in nucleocytoplasmic asynchrony. (cells not developing normally)
Pathophysiology
- Cellular Effects: Megaloblastosis affects various cells, including buccal mucosa, tongue, and gastrointestinal tract. Cells die, causing hypercellular bone marrow and ineffective erythropoiesis.
- Morphological Features: Mature RBCs are large and oval, potentially with nuclear remnants. Immature precursors (pre-RBC cells) appear as giant metamyelocytes with large nuclei. Neutrophils may show hypersegmentation.
- Hematological Impacts: Hemolysis in bone marrow leads to elevated bilirubin and lactate dehydrogenase (LDH) levels. Iron stores are usually elevated. Reticulocytosis (new RBC production) is absent.
- Neurological Implications (Vitamin B12 Deficiency): Up to 40% of cases in developing countries develop neurological problems. This involves focal demyelination in the spinal cord, peripheral nerves, optic nerves, and cerebrum.
- Symptoms: Common symptoms include malaise, breathlessness, and paraesthesia. Other potential symptoms: sore mouth, weight loss, impotence, memory problems, depression, personality changes, hallucinations and visual disturbances.
- Signs: Physical examination can reveal a smooth tongue, angular cheilosis (cracked lip corners), vitiligo, skin pigmentation changes, heart failure, and pyrexia.
Differentiation from other anemias
- Non-megaloblastic macrocytic anemia: Results from red cell membrane abnormalities. Large round RBCs, but normal neutrophils.
Vitamin B12 Absorption and Deficiency
- Absorption Mechanism: Vitamin B12 absorption involves gastric enzymes and intrinsic factor (produced by gastric parietal cells). The B12-intrinsic factor complex is absorbed in the terminal ileum and bound to transcobalamin II for transport.
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Causes of Deficiency:
- Dietary: Primarily affects strict vegans.
- Gastric Pathology: Conditions like hypochlorhydria (low stomach acid) or total gastrectomy result in B12 deficiency.
- Pernicious Anemia: An autoimmune disorder causing intrinsic factor deficiency.
- Small Bowel Pathology: Conditions affecting the terminal ileum or bacterial overgrowth interfere with absorption.
- Diagnosis: Anti-intrinsic factor antibodies are diagnostic for pernicious anemia. Anti-parietal cell antibodies are often present but not as definitive. Schilling test (less common) measures B12 absorption, aiding in differentiating causes.
Folate Absorption and Deficiency
- Absorption Mechanism: Folates come from plants and bacteria (vegetables, fruits, animal proteins). Average Western diets usually meet daily requirements, but cooking can reduce folate content. Total body folate stores are small.
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Causes of Deficiency:
- Poor Intake: Particularly in elderly or individuals with psychiatric conditions.
- Malabsorption: Conditions like Coeliac disease or small bowel surgery.
- Increased Demand: Situations like pregnancy or hemolysis (RBC destruction).
- Drug Interactions: Certain medications can disrupt folate metabolism.
- Diagnosis: Serum folate levels can be unreliable due to dietary intake variation. Red cell folate levels are a more accurate assessment of folate stores.
Management
- Initial Treatment: In severe cases, start with both folic acid and vitamin B12 before results are available to prevent worsening neurological symptoms. Consider blood transfusion for angina or heart failure.
- Vitamin B12 Treatment: Hydroxocobalamin (1000 µg IM) for six doses, followed by maintenance therapy every three months. Higher doses may be required for neurological involvement.
- Folate Treatment: Oral folic acid (5 mg daily for three weeks) and then weekly maintenance.
- Prophylaxis: Prophylactic folic acid is recommended during pregnancy and in chronic hematological diseases.
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Description
This quiz covers megaloblastic anaemia, including its definition, characteristics, and the roles of vitamin B12 and folate in DNA synthesis. Explore the pathophysiology, cellular effects, and the morphological features associated with this type of anaemia. Test your knowledge on how deficiencies can impact red blood cell production.
