Mystery Diagnosis had an episode about this where a lady went for like 11 years without drs diagnosing this correctly and all she needed was shots of B12. For some reason, taking it orally didnt help her.
Pernicious anemia develops slowly; the diagnosis is easily missed when the symptoms are mild.
The cause of pernicious anemia is the lack of intrinsic factor. Intrinsic factor is produced in the stomach and is required for B12 to be absorbed in the small intestine (distal ileum). In pernicious anemia, the stomach no longer produces intrinsic factor so B12 is cannot be absorbed from the GI tract. The only way to get B12 into the body is through injection. B12 deficiency can also result from surgery to the stomach if the area is removed where intrinsic factor is produced. Surgery on the ileum where B12 is absorbed can also result in deficiency.
B12 deficiency produces large red blood cells and iron deficiency anemia produces small cells. White cells and platelets are also impaired. As I mentioned in my earlier post, neurologic problems can also occur. Without B12, the nerves lose myelin, their protective coating. Symptoms can be diverse and include numbness, muscle weakness, personality changes, confusion, hallucinations and more