Contributor: Gordon K. Klintworth
Pernicious anemia (Addisonian pernicious anemia) is a megaloblastic anemia [anemia - megaloblastic] caused by a deficiency of cyanocobalamin [vitamin B12 deficiency]. Although a dietary deficiency of cyanocobalamin may cause the anemia most cases show a genetic predisposition and result from autoimmune gastritis in which there is a malabsorption of the vitamin due to a deficiency of intrinsic factor. Addisonian pernicious anemia in which the gastric mucosa is atrophic is by far the commonest cause of cyanocobalamin deficiency. The optic atrophy and retrobulbar neuritis, which is sometimes found in Addisonian pernicious anemia may be tocacco-alcohol amblyopia due to cyanide intoxication. This possibility is reinforced by evidence of a link between cyanocobalamin and the metabolism and detoxification of cyanide.