Vitamin B12 deficiency
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|Dementias
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|Vitamin B1 Thiamine deficiency
|Vitamin B12 deficiency
🧠 Neurological signs of Vitamin B12 deficiency can occur even without anaemia.
💉 Parenteral B12 may reverse peripheral neuropathy, but established spinal cord and brain damage is often irreversible.
📍 Vitamin B12 is actively absorbed in the terminal ileum with the aid of intrinsic factor.
ℹ️ About
- Vitamin B12 deficiency is common and has a wide spectrum of presentations, ranging from anaemia to irreversible neurological damage.
- Deficiency is usually due to malabsorption (e.g., pernicious anaemia, Crohn’s disease, post-gastrectomy) but can also result from strict vegan diets 🌱.
- The liver stores large amounts of B12, so deficiency often develops slowly over several years ⏳.
🥩 Sources of Vitamin B12
- Animal foods: red meat, poultry, fish 🐟, eggs 🥚, and dairy 🧀.
- Fortified foods: cereals, breads, plant-based alternatives 🌾.
- Brewer’s yeast (fortified preparations).
⚠️ Causes
- Pernicious Anaemia: Autoimmune destruction of intrinsic factor ❌.
- Terminal Ileal Disease: Crohn’s disease, ileal resection, ileitis.
- Post-Gastrectomy: Reduced intrinsic factor production.
- Parasites: Diphyllobothrium latum 🪱.
- Bacterial Overgrowth: Competes for B12.
- Strict Vegan Diet: No animal products 🌱.
- Rare: Transcobalamin II deficiency (genetic).
🩺 Clinical Features
- General: Fatigue 😴, lemon-yellow skin, glossitis 👅.
- Oral: Angular cheilitis, beefy sore tongue.
- Neurological:
- Brain: Dementia 🧠, cerebellar ataxia.
- Spinal Cord: Subacute combined degeneration →
- Loss of vibration sense 🎵 and proprioception.
- Positive Babinski sign 👣.
- Peripheral Nerves: Tingling/numbness in hands & feet ✋🦶.
- Ocular: Optic atrophy 👁️.
- Note: Neurological damage may occur without anaemia and can be irreversible ⚡.
🔬 Investigations
- FBC: Macrocytic anaemia (MCV >110 fL), hypersegmented neutrophils 🔍.
- Blood Film: Anisopoikilocytosis.
- Biochemistry: ↑ LDH, ↑ unconjugated bilirubin.
- Specific Tests:
- Intrinsic factor / parietal cell antibodies (pernicious anaemia) 🧪.
- Raised methylmalonic acid & homocysteine.
- Coeliac screen if suspected (anti-TTG).
- MRI: T2 hyperintensity in dorsal columns of cervical cord 📷.
🧾 Differential Diagnosis
- Copper deficiency 🪙: Mimics B12 neuropathy.
- Nitrous oxide abuse 🎈: Inactivates B12.
💊 Management
- Avoid Transfusion: Only in severe cases; risk of cardiac failure ❤️.
- Hydroxocobalamin (IM):
- 1 mg IM twice weekly × 3 weeks → then every 3 months lifelong (if irreversible cause).
- Folate: Add 5 mg daily if folate deficiency present 🌿.
- Monitor Potassium: Risk of hypokalaemia after replacement 🧂.
- Check Reticulocytes: Rise within 2–3 days ✅.
