Anemia is a condition of reduced hemoglobin levels; pernicious anemia (also known as Addi-son's anemia) is caused by a deficiency of or inability to use vitamin B12. Normally, vitaminB12 combines with the intrinsic factor, a substance that is secreted by the gastric mucosa, and then follows a path to the distal ileum, where it is absorbed and transported to body tissues. In pernicious anemia, intrinsic factor deficiency impairs vitamin B12 absorption. The deficiency of vitamin B12 inhibits the growth of red blood cells (RBCs) and leads to the production of insufficient and deformed RBCs with poor oxygen-carrying capacity. Because these deformed RBCs are known as megaloblasts (primitive, large, macrocytic cells), pernicious anemia is characterized as one of the megaloblastic anemias. Pernicious anemia is also caused by a deficiency of gastric hydrochloric acid (hypochlorhydria).
Complications caused by pernicious anemia include macrocytic anemia and gastrointestinal disorders. Pernicious anemia impairs myelin formation and thus alters the structure and disrupts the function of the peripheral nerves, spinal cord, and brain. Patients have a high incidence of benign gastric polyps, peptic ulcers, and gastric carcinoma. Low hemoglobin levels and consequent hypoxemia of long duration can result in congestive heart failure and angina pectoris in the elderly. If it is left untreated, pernicious anemia can cause psychotic behavior or even death.
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