This patient presented with a history of gradual lower limb weakness and sensory changes with no bladder or bowel disturbances. An MRI was performed to exclude a cord compression.

Subsequent investigations revealed macrocytic anemia with a very low vitamin B12 level of <37pmol/L  (normal >150). Homocysteine was also level elevated. 
Gastric parietal cell antibodies were weakly positive.

The patient usually had a full diet including fish, meat and vegetables. He had no significant prior background medical history.

The patient was treated and discharged on vitamin B12 injections and folate supplements.

Parietal cells in the stomach are required to produce Intrinsic Factor (IF) which is a protein that binds with Vitamin B12 from the diet to enable subsequent ileal Vitamins B12 absorption and red blood cell production.

Pernicious anemia is an autoimmune condition where antibodies against gastric parietal cells and inactivation of Intrinsic factor leading to atrophic gastritis. Impaired vitamin B12 absorption leads to megaloblastic anemia with abnormally large red blood cells called macrocytes being produced. Pernicious anemia is one of the causes of macrocytic anemia, other causes include diet, chronic alcoholism and medication-related causes.