Vitamin B12 is found in beef liver, oysters, and tuna. Vitamin B12 affects myelin formation. Vitamin B12 deficiency takes years to develop. Vitamin B12 deficiency leads to peripheral neuropathy and pernicious anemia, muscle weakness and movement problems, and memory problems.
In pernicious anemia labs will show MCV > 100, low
hemoglobin concentration and low RBC count.
Vitamin B12 levels should be obtained in patients with
peripheral sensory neuropathy (normal values are 200-900 picograms per
milliliter).
Risk factors for developing Vitamin B12 deficiency include
gastric resection surgery, chronic pancreatitis, severe malnutrition and vegan
diet. In the gut, Vitamin B12 is carried on intrinsic factor which protects it
from proteolytic enzymes. Intrinsic factor also helps the vitamin to be
absorbed in the terminal ileum.
The nervous system is affected in three parts:
- The dorsal column:
Affection of the dorsal column leads to problems in positions
and vibration sensation as well as sensory ataxia.
- The lateral corticospinal tracts:
Affection of the lateral corticospinal tracts leads to
hyperreflexia, spasticity and pathological reflexes which are all signs of
upper motor neuron involvement.
- Peripheral nerves:
Axonal degeneration of the peripheral nerves leads to
numbness and paresthesia.
