Makindo Medical Notes

Related Subjects: |Dementias |Abbreviated Mental Test Score (AMTS)

Neurological signs of B12 deficiency can be present even without anaemia. Parenteral B12 reverses nerve damage but has little effect on the spinal cord and brain. Vitamin B12 is actively absorbed in the terminal ileum.

About

• Vitamin B12 deficiency has various causes, often related to malabsorption, dietary restrictions, or specific conditions (see causes for details).

Sources of Vitamin B12

• Lean red meats, poultry, fish, brewer's yeast, and dairy products such as milk, cheese, and yoghurt.
• Fortified foods: Some breakfast cereals, breads, and other products are fortified with Vitamin B12.

Causes

• Pernicious Anaemia: Autoimmune destruction of intrinsic factor, preventing B12 absorption.
• Terminal Ileal Disease: Crohn's disease, surgical resection, or ileitis affecting absorption.
• Post-Gastrectomy: Reduced intrinsic factor production after stomach surgery.
• Diphyllobothrium latum Infection: Parasitic infection can deplete B12.
• Bacterial Overgrowth/Blind Loop Syndrome: Bacteria compete for B12 in the intestines.
• Strict Vegan Diet: Lack of animal-based foods which are primary B12 sources.
• Transcobalamin II Deficiency: Rare genetic disorder affecting B12 transport.

Clinical Features

• General Symptoms: Fatigue, glossitis (inflamed tongue), anaemia, and yellowish skin.
• Oral Signs: Angular cheilosis, sore and beefy red tongue.
• Ocular Signs: Optic atrophy and, less commonly, retinal haemorrhage.
• Neurological Symptoms:
  • Brain: Dementia, cerebellar ataxia (difficulty with coordination).
  • Spinal Cord: Dorsal column and corticospinal tract involvement causing:
    • Loss of vibration sense and proprioception.
    • Positive Babinski sign (extensor plantar response) and increased reflexes.
  • Peripheral Nervous System: Sensorimotor polyneuropathy presenting as numbness, tingling in fingers and toes, and absent ankle jerks.
  • Note: Brain and spinal cord damage from B12 deficiency may be irreversible.

Investigations

• Full Blood Count (FBC): Macrocytic megaloblastic anaemia (MCV > 110 fL) is common.
  • Possible isolated red cell macrocytosis without anaemia.
  • Macrocytic anaemia, especially if MCV >110 fL.
  • Pancytopenia may be seen in severe cases (MCV >120 fL).
  • Anisopoikilocytosis (variation in red cell shape).
• Presence of hypersegmented polymorphs and low WBC and platelet counts.
• Bone Marrow: Megaloblastic changes.
• Other Tests:
  • Raised unconjugated bilirubin and LDH.
  • Intrinsic factor antibody assay (+ve in 50% of patients with pernicious anaemia).
  • Anti-TTG antibodies or jejunal biopsy if coeliac disease is suspected.
  • Raised methylmalonic acid and homocysteine levels (indicators of B12 deficiency).
  • MRI: T2-weighted signal changes in cervical spinal cord, especially in the dorsal columns.

Differential Diagnosis

• Copper Deficiency: Can cause a similar myelopathy and neuropathy.
• Nitrous Oxide Abuse: Can inactivate B12, leading to similar neurological symptoms.

Management

• Avoid Transfusion: Blood transfusions are typically avoided due to the risk of cardiac failure; if needed, proceed cautiously with diuretic cover and close monitoring.
• Vitamin B12 (Hydroxocobalamin):
  • Administer 1 mg intramuscularly twice a week for 3 weeks, then every 3 months for life.
• Additional haematinics like folate (5 mg daily) may be required alongside B12.
• Potassium Monitoring: Sudden B12 and folate replacement can lead to hypokalaemia due to a surge in red blood cell production, so potassium levels should be monitored.
• Reticulocyte Count: Should rise within 2-3 days of B12 administration, indicating a positive response.