Saturday, 25 September 2010

MRCP revision battle 20.4: Vitamin B12

Vitamin B12 is essential in DNA synthesis.  The body has approximately 4 yrs worth of B12 stored, 'just in case.'

B12 is found in meat and dairy, so other than vegans most people should get enough.

Absorption of B12 is specific; it requires intrinsic factor (which is released from parietal cells in the stomach) to bind to it and it is then absorbed as a complex uniquely in the terminal ileum.

Deficiency of B12 causes a variety of symptoms and signs:
  • anaemia
  • glossitis
  • dementia/depression
  • peripheral neuropathy
  • subacute combined degeneration of the spinal cord

Investigations will show a macrocytic anaemia, and in severe cases WCC and platelets may also be decreased.

Causes of B12 deficiency can be split into:
  • insufficient intake
    • vegans
    • alcoholics
    • anorexics
  • lack of absorption
    • lack of intrinsic factor
      • pernicious anaemia (see next battle)
      • gastrectomy
    • lack of terminal ileum/absorption space
      • crohns
      • resection
      • giardiasis
      • fish tapeworm, Diphyllobothrium 
      • drugs interfering with absorption, eg metformin

Treatment is to treat the cause/give B12.

Lets have a quick look at pernicious anaemia...