Pernicious anemia is a disease in which the red blood cells are abnormally formed, due to an inability to absorb vitamin B12. Vitamin B12, or cobalamin, plays an important role in the development of red bloodcells. It is found in significant quantities in liver, meats, milk and milk products, and legumes. During the course of the digestion of foods containingB12, the B12 becomes attached to a substance called intrinsic factor. Intrinsic factor is produced by parietal cells which line thestomach. The B12-intrinsic factor complex then enters the intestine, where the vitamin is absorbed into the bloodstream. In fact, B12 can only be absorbed when it is attached to intrinsic factor.
In pernicious anemia, the parietal cells stop producing intrinsic factor. Theintestine is then completely unable to absorb B12. So, the vitamin passes out of the body as waste. Although the body has significant amountsof stored B12, this will eventually be used up. At this point, thesymptoms of pernicious anemia will develop.
Pernicious anemia is most common among people from northern Europe and amongAfrican Americans. It is far less frequently seen among people from southernEurope and Asia. Pernicious anemia occurs in equal numbers in both men and women. Most patients with pernicious anemia are older, usually over 60. Occasionally, a child will have an inherited condition which results in defective intrinsic factor. Pernicious anemia seems to run in families, so that anyone with a relative suffering from the disease has a greater likelihood of developing it as well.
People with pernicious anemia seem to have a greater chance of having certainother conditions. These conditions include autoimmune disorders, particularly those affecting the thyroid, parathyroid, and adrenals. It is thought thatthe immune system, already out of control in these diseases, incorrectly becomes directed against the parietal cells. Ultimately, the parietal cells seemto be destroyed by the actions of the immune system.
True pernicious anemia refers specifically to a disorder of decayed parietalcells leading to absent intrinsic factor, resulting in an inability to absorbB12. However, there are other related conditions which result indecreased absorption of B12. These conditions cause the same typesof symptoms as true pernicious anemia. Other conditions which interfere witheither 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, foruse in their own growth. Intestinal worms (especially one called fish tapeworm) may also use B12, resulting in anemia. Various conditions thataffect the first part of the intestine (the ileum), from which B12is 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 theproper formation of red blood cells. Without B12, red blood cellproduction is greatly reduced. Those red blood cells that are produced are abnormally large and defective 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 brightlyred 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.
Diagnosis of pernicious anemia is suggested when a blood test reveals abnormally large red blood cells. Many of these will also be abnormally shaped. Theearliest, least mature forms of red blood cells (reticulocytes) also will below in number. White blood cells and platelets may also be decreased in number. Measurements of the quantity of B12 circulating in the bloodstream will be low. Testing for true pernicious anemia is more complex.
Treatment of pernicious anemia requires the administration of lifelong injections of B12. Vitamin B12 given by injection enters thebloodstream directly, and doesn't require intrinsic factor. At first, injections may need to be given several times a week, in order to build up adequatestores of the vitamin. After this, the injections can be given on a monthly basis. Other substances required for blood cell production may also need to begiven; they may include iron and vitamin C.
Prognosis is generally good for patients with pernicious anemia. Many of thesymptoms improve within just a few days of beginning treatment, although someof the nervous system symptoms may take up to 18 months to improve. Occasionally, when diagnosis and treatment have been delayed for a long time, some ofthe nervous system symptoms may be permanent.
Because an increased risk of stomach cancer has been noted in patients with pernicious anemia, careful monitoring is necessary, even when all the symptomsof the original disorder have improved.