Pernicious Anemia: Causes and symptoms
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Intrinsic factor is produced by specialized cells within the stomach called parietal cells. When these parietal cells shrink in size (atrophy), they produce less and less intrinsic factor. Eventually, the parietal cells stop functioning altogether. Other important products of parietal cells are also lessened, including stomach acid, and an enzyme involved in the digestion of proteins.
People with pernicious anemia seem to have a greater chance of having certain other conditions. These conditions include autoimmune disorders, particularly those affecting the thyroid, parathyroid, and adrenals. It is thought that the immune system, already out of control in these diseases, incorrectly becomes directed against the parietal cells. Ultimately, the parietal cells seem to be destroyed by the actions of the immune system.
As noted, true pernicious anemia refers specifically to a disorder of atrophied parietal cells leading to absent intrinsic factor, resulting in an inability to absorb B12. However, there are other related conditions which result in decreased absorption of B12. These conditions cause the same types of symptoms as true pernicious anemia. Other conditions that interfere with either the production of intrinsic factor, or the body's use of B12, include conditions that require surgical removal of the stomach, or poisonings with corrosive substances which destroy the lining of the stomach. Certain structural defects of the intestinal system can result in an overgrowth of normal bacteria. These bacteria then absorb B12 themselves, for use in their own growth. Intestinal worms (especially one called fish tapeworm) may also use B12, resulting in anemia. Various conditions that affect the first part of the intestine (the ileum), from which B12 is absorbed, can also cause anemia due to B12 deficiency. These ilium related disorders include tropical sprue, Whipple's disease, Crohn's disease, tuberculosis, and the Zollinger-Ellison syndrome.
Symptoms of pernicious anemia and decreased B12 affect three systems of the body: the system that is involved in the formation of blood cells (hematopoietic system); the gastrointestinal system; and the nervous system.
The hematopoietic system is harmed because B12 is required for the proper formation of red blood cells. Without B12, red blood cell production is greatly reduced. Those red blood cells that are produced are abnormally large and abnormal in shape. Because red blood cells are responsible for carrying oxygen around the body, decreased numbers (termed anemia) result in a number of symptoms, including fatigue, dizziness, ringing in the ears, pale or yellowish skin, fast heart rate, enlarged heart with an abnormal heart sound (murmur) evident on examination, and chest pain.
Symptoms that affect the gastrointestinal system include a sore and brightly red tongue, loss of appetite, weight loss, diarrhea, and abdominal cramping.
The nervous system is severely affected when pernicious anemia goes untreated. Symptoms include numbness, tingling, or burning in the arms, legs, hands, and feet; muscle weakness; difficulty and loss of balance while walking; changes in reflexes; irritability, confusion, and depression.
— Rosalyn Carson-DeWitt, MD
