Pernicious anemia
Pernicious anemia is a type of megaloblastic anemia caused by the body's inability to absorb vitamin B12, which is essential for the production of healthy red blood cells and the maintenance of nerve function. This condition arises when there is a lack of intrinsic factor, a protein produced in the stomach necessary for the absorption of vitamin B12. Although it can occur due to dietary deficiencies, pernicious anemia is often linked to autoimmune conditions that damage the stomach lining, particularly in older adults. Symptoms include fatigue, depression, and neurological issues, including numbness and difficulty walking. Diagnosis typically involves blood tests that evaluate red blood cell characteristics and vitamin B12 levels. Treatment varies based on the underlying cause but may include dietary changes or vitamin B12 injections. Early detection and treatment are crucial, as untreated pernicious anemia can lead to severe complications, including neurological damage and even death. The condition is more prevalent among older adults and certain ethnic groups, notably those of Northern European descent.
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Pernicious anemia
Pernicious anemia is a type of anemia that results from inadequate intake of vitamin B12 in the diet. Vitamin B12 is an essential vitamin that cannot be made by the human body and must be obtained through diet; however, even with adequate intake of vitamin B12 in the diet the condition of the stomach lining and presence of intrinsic factor determines whether the body can absorb the nutrient from food. Vitamin B12 is responsible for keeping nerves and red blood cells healthy. In healthy individuals, the liver can store three to five years of vitamin B12, but as humans age, the ability to make intrinsic factor weakens. Data published in the Journal of Blood Medicine (2012) estimates that the disease affects approximately 0.1 percent of the general population, and approximately 1.9 percent of those individuals aged sixty years or older. The prevalence of pernicious anemia is higher in Northern European (particularly Scandinavia) and African countries or individuals descended from these regions. Though pernicious anemia is easily treatable when detected in early stages, the disease can be fatal if allowed to progress.
Background
Pernicious anemia was first discovered by a physician named Thomas Addison (1855), who was examining a patient that was pale and weak. After this case, many physicians over the next thirty years noticed patients who were also pale, weak, and had enlarged, sore, red tongues. Some of these patients had numbness and tingling in their fingers and toes which progressed to difficulty walking. When a physician took a blood sample, he observed large, oval-shaped erythrocytes (red blood cells), as well as a lack of acid in the patient’s stomach. Using these symptoms to characterize the disease, it was called pernicious anemia. By 1908, a physician named Richard Cabot reported that once patients became symptomatic (showing signs of a disease), they only lived between one-to-three years later.
Francis Weld Peabody, a physician-scientist of the early twentieth century, further characterized the effects that the disease had on erythrocytes removed from a patient’s bone marrow. Also, George Whipple conducted experiments using dogs to show how diet (specifically liver) could help regenerate the quantity and integrity of erythrocytes after depleting the animal’s supply with phlebotomy. Armed with this important discovery, George Richards Minot and William Murphy began conducting experiments in human patients, using a diet rich in liver, in hopes of regenerating erythrocytes. After a week, the blood of the patients being treated showed a significant increase in erythrocytes. After two to four months of treatment, the patients’ erythrocyte counts were within normal range and symptoms had largely disappeared. In 1934, Minot, Murphy, and Whipple received the Nobel Prize in Physiology or Medicine for this important discovery. Later it was discovered that vitamin B12 was the component in liver that was responsible for improvement in erythrocyte count.
Overview
Pernicious anemia is one of many different types of megaloblastic anemias. It is also known as vitamin B12 anemia. Anemia is a condition where the body doesn’t have enough healthy erythrocytes to properly oxygenate tissues. There are several known factors that can lead to the development of the disease: lack of vitamin B12 in the diet, lack of intrinsic factor in the stomach to digest and absorb vitamin B12, and though not clearly understood, infection with Helicobacter pylori of the stomach lining. Also, gastric removal surgery can cause inability to absorb vitamin B12 when parts of the stomach that produces stomach acid are removed or bypassed. However, this only causes partial malabsorption and the body’s liver storage of vitamin B12 is usually adequate to provide the body with enough of the nutrient.
When foods that contain vitamin B12 are consumed, the vitamin binds to protein called intrinsic factor (most efficiently to animal protein), which is synthesized by parietal cells in the gastric mucosa of the stomach, and is released by gastric acid. The compound is then absorbed through the small intestine and is metabolized by the liver.
The most common reason for vitamin B12 deficiency is the inability to absorb the vitamin due to lack of intrinsic factor, usually a part of the aging process. One reason for the lack of intrinsic factor is an autoimmune condition that results in atrophy (shrinking) of the gastric mucosa due to destruction of parietal cells. Without intrinsic factor vitamin B12 cannot be absorbed in the small intestine.
Pernicious anemia progresses slowly. Signs and symptoms of pernicious anemia are low erythrocyte count, fatigue, depression, low-grade fever, diarrhea, nausea, weight loss, sore tongue, pain in the limbs (neuropathic pain), and sores in the corners of the mouth (chelitis). Patients who have more advanced disease can also exhibit nervous system changes, such as impaired thinking and memory, psychosis, impaired urination, loss of sensation in feet, walking difficulties, and muscle weakness. In children and adolescents, pernicious anemia can cause stunted growth or even delay puberty in certain individuals.
Diagnosis of pernicious anemia is based on enlarged, oval erythrocytes found in a blood smear, in conjunction with a low erythrocyte count. The two measurements used to help diagnose pernicious anemia are Mean Corpuscular Hemoglobin Concentration (MCHC), to determine hemoglobin (oxygen-carrying capacity of erythrocytes) concentration, and Mean Corpuscular Volume (MCV). A physician will also obtain vitamin B12 levels in the blood, though alone this information does not help distinguish the cause of the anemia. Also, not all tests for vitamin B12 are reliable in terms of level of the nutrient in the blood.
A non-laboratory test for pernicious anemia, which is no longer widely used, is the Schilling test. The Schilling test involves the patient taking an oral dose of radiolabeled vitamin B12. Then the amount of radioactive metabolites excreted within a 24-hour period is measured. Next, the patient takes another dose of radiolabeled vitamin B12 with the addition of a dose of intrinsic factor (similar to Castle’s experiment), and the amount of radioactive metabolites excreted are measured. If the patient has more radioactive metabolites after the dose of intrinsic factor, then a diagnosis of vitamin B12 deficiency due to lack of intrinsic factor is made.
Pernicious anemia treatment is determined by the cause. If there are low dietary levels of vitamin B12, then the physician will prescribe an increase of vitamin B12-rich foods, such as liver, red meat, and even supplements. If the cause is due to lack of intrinsic factor, then the physician will prescribe vitamin B12 injections at varying intervals. Patients who are diagnosed early have the best chance at living a normal, healthy life. If a patient is not treated in time, neurological complications, fatigue, depression, and even death, can occur.
Bibliography
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