Vitamin B12 deficiency

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 cord and brain. Vitamin B12 is actively absorbed in the Terminal Ileum

About

• Various causes - see pernicious anaemia

Source

• Lean red meats, poultry, fish, brewer's yeast, and dairy products, such as milk, cheese, and yoghurt.
• Vitamin B12 is also added to some breakfast cereals, breads, and other fortified food products.

Causes

• Pernicious anaemia
• Terminal ileal disease/Crohn's disease
• Post Gastrectomy
• Diphyllobothrium infection
• Bacterial overgrowth/Blind loop syndrome
• Vegan diet
• Disorders of terminal ileum (site of absorption): crohn's, blind-loop etc
• Transcobalamin II deficiency

Clinical

• Fatigue, Glossitis, Anaemia, Yellowish skin
• Angular cheilosis, Sore beefy red tongue
• Eyes: Optic atrophy and retinal haemorrhage can be seen
• Brain: Dementia and cerebellar ataxia
• Spinal cord: Dorsal column vibration and proprioception loss as well as a corticospinal loss: extensor plantars and ++ Knee jerk. This is subacute combined degeneration of the cord.
• Peripheral nervous system: Sensorimotor Polyneuropathy - numbness and tingling of fingers and toes, distal sensory loss, absent ankle jerks
• Brain and spinal cord damage is irreversible

Investigations

• FBC: Macrocytic megaloblastic anaemia MCV > 110 fL
  • Isolated red cell macrocytosis without anaemia
  • Macrocytic anaemia (esp if MCV >110fl)
  • Pancytopenia (esp if MCV >120fl)
  • Anisopoikilocytosis
• Hypersegmented polymorphs and low WCC and thrombocytopenia
• Bone marrow: megaloblastic
• Unconjugated hyperbilirubinemia
• Intrinsic factor antibody assay (+ve in 50% of patients with PA)
• Anti-TTG antibodies/jejunal biopsy ? Coeliac
• Raised LDH, ? Methylmalonic acid and Homocysteine
• MRI: MRI reveals abnormal high T2 cervical cord signal within the bilateral dorsal columns

Differential

• Copper deficiency
• Nitrous oxide abuse

Management

• Generally try to avoid transfusion as high risk of cardiac failure. If the patient is haemodynamically compromised then may require transfusion please do so very carefully as can precipitate heart failure. Give with diuretic cover and frequent monitoring.
• Give Vitamin B12 (Hydroxocobalamin) 1 mg twice a week im for 3 weeks and then every 3 months for life.
• May also require additional haematinics such as folate 5 mg OD
• Sudden B12 and folate can cause a burst in haemopoiesis and often potassium is in high demand and should be given to avoid hypokalaemia
• The reticulocyte count should rise in 2-3 days