Pernicious anaemia is a cause of B12 deficiency anaemia. B12 deficiency can be caused by insufficient dietary intake of vitamin B12 or pernicious anaemia.
The parietal cells of the stomach produce a protein called intrinsic factor. Intrinsic factor is essential for the absorption of vitamin B12 in the ileum.
Pernicious anaemia is an autoimmune condition where antibodies form against the parietal cells or intrinsic factor. A lack of intrinsic factor prevents the absorption of vitamin B12 and the patient becomes vitamin B12 deficient.
Vitamin B12 deficiency can cause neurological symptoms:
- Peripheral neuropathy with numbness or paraesthesia (pins and needles)
- Loss of vibration sense or proprioception
- Visual changes
- Mood or cognitive changes
TOM TIP: For your exams remember testing for vitamin B12 deficiency and pernicious anaemia in patients presenting with peripheral neuropathy, particularly with pins and needles.
Testing for auto-antibodies is used to diagnose pernicious anaemia.
- Intrinsic factor antibody is the first line investigation
- Gastric parietal cell antibody can also be tested but is less helpful
Dietary deficiency can be treated with oral replacement with cyanocobalamin unless the deficiency is severe.
In pernicious anaemia oral replacement is inadequate because the problem is with absorption rather than intake. They can be treated with 1mg of intramuscular hydroxycobalamin 3 times weekly for 2 weeks, then every 3 months. More intense regimens are used where there are neurological symptoms (e.g. 1mg every other day until the symptoms improve).
If there is also folate deficiency it is important to treat the B12 deficiency first before correcting the folate deficiency. Treating patients with folic acid when they have a B12 deficiency can lead to subacute combined degeneration of the cord.
Last updated April 2019