Pernicious Anemia

Pernicious anemia (also known as Biermer's anemia, Addison's anemia, or Addison–Biermer anemia) is one of many types of the larger family of megaloblastic anemias. It is caused by loss of gastric parietal cells which are responsible, in part, for the secretion of intrinsic factor, a protein essential for subsequent absorption of vitamin B₁₂ in the ileum.

Usually seated in an atrophic gastritis, the autoimmune destruction of gastric parietal cells (and autoantibody inactivation of intrinsic factor) leads to a lack of intrinsic factor. Since the absorption from the gut of normal dietary amounts of vitamin B₁₂ is dependent on intrinsic factor, the loss of intrinsic factor leads to vitamin B₁₂ deficiency. While the term 'pernicious anemia' is sometimes also incorrectly used to indicate megaloblastic anemia due to 'any' cause of vitamin B₁₂ deficiency, its proper usage refers to that caused by atrophic gastritis, parietal cell loss, and lack of intrinsic factor only.

The loss of ability to absorb vitamin B₁₂ (B₁₂) is the most common cause of adult B₁₂ deficiency. Such a loss may be due to pernicious anemia (with loss of intrinsic factor) or to a number of other conditions that decrease production of gastric acid, which also plays a part in absorption of B₁₂ from foods.

Historically, pernicious anemia (PA) was detected only after it became "clinical" (caused an overt disease state) and the anemia was well established, i.e., liver stores of B₁₂ had been depleted. The "pernicious" aspect of the disease - prior to the discovery of treatment - was its invariably fatal prognosis, similar to leukemia at that time. However, in the time since elucidation of the cause of the disease, modern tests that specifically target B₁₂ absorption can be used to diagnose the disease before it becomes clinically apparent. In such cases, the disease may be diagnosed and treated without the patient ever becoming ill.

Replacement of vitamin stores does not correct the defect in absorption from loss of intrinsic factor. Since the defect defines the disease, a person without the ability to absorb B₁₂ in this way will have pernicious anemia for the remainder of his or her life. However, unless the patient has sustained permanent peripheral nerve damage before treatment, regular B₁₂ replacement will keep PA in check, with no anemia and no further symptoms.

Although initial treatment of the disease usually involves injections of B₁₂ to rapidly replace body stores, a number of studies have shown long-term vitamin replacement treatment may be maintained with high-dose oral B₁₂ supplements, since sufficient B₁₂ is absorbed from these by a normal intestine, even without any intrinsic factor. In this regard, nasal and sublingual forms of B₁₂ have not been found to have any special value over simple swallowed tablets.