Pernicious anemia is a rare blood disorder characterized by the inability of the body to properly utilize vitamin B12, from a deficiency of cobalamin (vitamin B12), which in turn is caused by a lack of intrinsic factors (IF) that are essential for the development of red blood cells. An intrinsic factor is a glycoprotein that binds cobalamin and thereby enables its absorption in the terminal ileum. Pernicious anemia is often described as an autoimmune disorder due to the findings of gastric autoantibodies directed against both IF and parietal cells and the increased frequency of other autoimmune diseases seen in patients with pernicious anemia. Most cases result from the lack of gastric protein known as intrinsic factor, without which vitamin B12 cannot be absorbed.
The symptoms of pernicious anemia may include weakness, fatigue, an upset stomach, an abnormally rapid heartbeat (tachycardia), and/or chest pains. Recurring episodes of anemia (megaloblastic) and an abnormal yellow coloration of the skin (jaundice) are also common. Pernicious anemia is thought to be an autoimmune disorder, and certain people may have a genetic predisposition to this disorder.
There is a rare congenital form of pernicious anemia in which babies are born lacking the ability to produce effective intrinsic factors. There is also a juvenile form of the disease, but pernicious anemia typically does not appear before the age of 30. The onset of the disease is slow and may span decades. When the disease goes undiagnosed and untreated for a long period of time, it may lead to neurological complications. Nerve cells and blood cells need vitamin B12 to function properly.
Symptoms
Symptoms of pernicious anemia may include fatigue, shortness of breath, rapid heart rate, jaundice or pallor, tingling and numbness of hands and feet, loss of appetite, diarrhea, unsteadiness when walking, bleeding gums, impaired sense of smell, and confusion. Symptoms may include fatigue, pallor, paresthesia, incontinence, psychosis, and generalized weakness.
The symptoms of juvenile pernicious anemia are usually obvious between the ages of 4 and 28 months. Most affected infants develop a form of anemia known as megaloblastic anemia. Large, immature red blood cells are found in the blood (megaloblasts), impairing the ability of the blood to deliver oxygen to the tissues of the body. Other types of blood cells (e.g., platelets and white blood cells) may also be deficient (pancytopenia). Symptoms may include vomiting, diarrhea, fatigue, headache, inability to sleep (insomnia), lack of appetite, failure to thrive, yellow coloration of the skin (jaundice), irritability, and/or a pale complexion. Mental retardation is also common in infants with juvenile pernicious anemia. Affected infants may experience repeated episodes of extreme anemia and jaundice. Some children with the juvenile form of the disease have blood protein present in their urine (persistent proteinuria) and some may have urinary tract malformations.
Individuals with congenital pernicious anemia present with symptoms very similar to the juvenile form. These however progress comparatively slowly; so slowly that the signs of neurological deficits may precede those associated with the decline in blood capacity. The symptoms may include generalized weakness and fatigue, difficulty breathing (dyspnea), an abnormally rapid heartbeat (tachycardia), and/or chest pains (angina). Affected individuals may also have gastrointestinal problems, such as a profound lack of appetite (anorexia), abdominal pain, indigestion, belching, and/or constipation and diarrhea. Weight loss is also common. Some people with Pernicious Anemia may have an abnormally enlarged liver (hepatomegaly) or spleen (splenomegaly). Other problems involving urinary function may also develop.
Because nerve cells need vitamin B12 to function properly, some people with pernicious anemia will display neurological symptoms. Nerves other than those of the brain and spinal cord (peripheral nervous system) are frequently affected. Occasionally, the spinal cord may also be involved. Neurological symptoms may include numbness, tingling, loss of sensation in the arms and/or legs (acroparesthesias). Other neurological symptoms may include impaired ability to coordinate movement (ataxia), a positive Babinski sign (outward motion of the big toe caused by stroking the sole of the foot), and/or exaggerated reflexes (hyperreflexia). Some people with pernicious anemia may also become extremely irritable or depressed and, in some rare cases, even experience paranoia (megaloblastic madness).
Causes
Pernicious anemia is thought to be an autoimmune disease. Autoimmune disorders are caused when the body’s natural defenses (e.g., antibodies) against “foreign” or invading organisms begin to attack healthy tissue for unknown reasons. Pernicious anemia is sometimes seen in association with certain autoimmune endocrine diseases, such as type 1 diabetes, hypoparathyroidism, Addison’s disease, and Graves’ disease.
However, since the disorder also tends to occur with greater frequency in certain families than in others, it is also believed that there may be a genetic component to pernicious anemia. In general, risk factors for pernicious anemia include a family history of the disease, being of Northern European or Scandinavian descent, and a history of autoimmune endocrine disorders.
The congenital and juvenile forms are thought to be inherited as autosomal recessive traits. The gene responsible for anemia due to intrinsic factor deficiency has been tracked to a location on chromosome 11 (11q13). The gene responsible for anemia due to the intestinal malabsorption of vitamin B12 has been tracked to sites on chromosomes 14 (14q32) and 10 (10p12.1).
Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 11q13” refers to band 13 on the long arm of chromosome 11. Similarly, gene map loci 14q32 and 10p12.1 refer to a site at band 32 on the long arm of chromosome 14, and at band 12.1 on the short arm of chromosome 10. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Genetic diseases are determined by the combination of genes for a particular trait that is on the chromosomes received from the father and the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier of the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
All individuals carry a few abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Autoimmune
Autoimmune gastritis is characterized by the destruction of gastric parietal cells and the resulting lack of the glycoprotein intrinsic factor secreted by these cells. The antibodies identified with autoimmunity are intrinsic factor antibodies (IFA) and parietal cell antibodies (PCA).
Parietal cell antibodies work against the parietal cell proton pump ATPase. The primary targets of parietal cell antibodies are the alpha and beta proton pump subunits. Research has determined that parietal cell antibodies are immunoglobulins from the M, G, and A isotypes, which operate against both subunits.[rx]
Intrinsic factor antibodies are immunoglobulin G isotype, and they can be either type 1 or type 2 antibodies. Type 1 conducts against the cobalamin binding site. Type 2 acts against the ileal mucosa receptor.[rx]
Other autoimmune diseases include pernicious anemia, which can be associated with autoimmune diseases, such as type 1 diabetes (3% to 4%), vitiligo (2% to 8%), and autoimmune thyroid disease (3% to 32%). This association has led to studies exposing that HLA alleles may be related to autoimmune gastritis. HLA-DRB1/03 and HLA-DRB1/04 alleles may predispose to autoimmune gastritis.[rx][rx]
Genetic
Researchers have also identified congenital and juvenile forms of pernicious anemia, which are thought to follow an autosomal recessive inheritance pattern.
Other causes of cobalamin deficiency include:
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Vegetarian diet
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Loss of gastric mucosa (gastrectomy, use of H2 blockers)
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Insufficient pancreatic enzymes (ZES, chronic pancreatitis)
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Tapeworm infestation
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Bacterial overgrowth
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Defects in the ileal mucosa leading to poor uptake of cobalamin
Diagnosis
The diagnosis of pernicious anemia may be confirmed by a thorough clinical evaluation, including detailed patient history and specialized laboratory tests. During a Schilling test, the intestines’ ability to absorb vitamin B12 is measured. The vitamin is labeled with radioactive cobalt and is ingested by mouth. X-ray studies can then determine if the body is properly absorbing this vitamin.
The clinician should also conduct a complete physical exam emphasizing hematological, gastrointestinal, and neurological findings.
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Hematological manifestations: pallor, fatigue, shortness of breath, dizziness, tachycardia, lightheadedness, and decreased cognitive and physical function
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Gastrointestinal manifestations: abdominal bloating, loss of appetite, weight loss, and diarrhea
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Neurological manifestations: Peripheral neuropathy, paresthesia, weakness, ataxia, forgetfulness, and psychosis
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Cardiac symptoms may include dyspnea, palpitations, and edema.
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Urinary retention as a result of spinal cord damage can also occur.
Pernicious anemia, if left untreated, may be fatal. The physical findings may include:
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Low-grade fever
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Beefy red tongue
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Tachycardia
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Blotchy skin pigmentation
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Altered mental status
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Visual deficits
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Enlarged liver if heart failure is present
Initial lab tests include:
Complete blood count (CBC), serum B12 levels, and a peripheral smear. The CBC should demonstrate anemia, as shown by decreased hemoglobin and hematocrit (hemoglobin concentration less than 13 g/dL for men and less than 12 g/dL for women). The mean corpuscular volume (MCV) would be greater than or equal to 100 fL, an expected finding in macrocytic anemia. The peripheral blood smear may demonstrate hyper-segmented neutrophils (neutrophils with five lobes or greater). B12 levels of under 200 pg/mL are considered deficient. Indirect bilirubin and lactate dehydrogenase levels are usually elevated due to the rapid breakdown of red blood cells.
After initial lab tests confirm B12 deficiency, the diagnosis of pernicious anemia will depend on further testing, such as the presence of atrophic body gastritis (ABG) and intrinsic factor deficiency.[rx] One must rule out folic acid deficiency. Many patients with pernicious anemia will have elevated serum homocysteine and methylmalonic acid levels. Methylmalonic aciduria in the absence of an inborn error of methylmalonic acid metabolism confirms cobalamin deficiency. Diagnostic criteria for ABG require a histological sampling of gastric body mucosa. Findings associated with PA are the presence of corpus-restricted atrophy with a spared antrum, as well as the presence of hyperplasia of ECL cells. Serological markers can also help identify ABG; for example, increased levels of fasting gastrin and decreased levels of pepsinogen I suggest the presence of mucosal damage. Anti-intrinsic factor antibodies and anti-parietal cell antibodies should be evaluated in patients with a high probability of disease, even if B12 levels are normal. Some patients can have severe neurologic symptoms with falsely normal B12 levels.
Intrinsic factor deficiency can be evaluated by the Shilling test, which is now being replaced by other diagnostic strategies such as detecting intrinsic factor antibodies. Antibodies to intrinsic factor can be of two types. One is the blocking type against the B12 binding site present in 70% of patients, and the other is antibodies to parietal cells present in 90% of patients, but it is less specific.
Alternative and new approaches to the diagnosis of PA are under evaluation. One of these is a newer propriety cobalamin absorption test, which has its basis in measuring the change in holoTC following oral ingestion of non-radiolabeled cobalamin. Another approach has been described using accelerator mass spectrometry to quantify 14C in the blood following an orally administered dose of [14C]-cyanocobalamin.[rx] One may empirically administer vitamin B12 intramuscularly and assess the response if cobalamin deficiency is suspected. Most patients will feel clinically better within 24 hours. Additionally, marked reticulocytosis will appear within 5 to 7 days.
It is important to know that falsely low levels of cobalamin may occur in the following situations:
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Multiple myeloma
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Pregnancy
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Use of hormonal therapy or oral contraceptives
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Severe folic acid deficiency
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High levels of ascorbic acid
Treatment
If pernicious anemia is ignored, undiagnosed, or left untreated, life-threatening complications can occur. Pernicious anemia is treated by the injection of vitamin B12 (hydroxocobalamin or cyanocobalamin) into the muscle. A physician must closely monitor the amount of vitamin that is given and adjust the dosage when necessary. People with pernicious anemia must continue to receive maintenance doses of vitamin B12 throughout life.
Patients generally receive an intramuscular injection of 1000 mcg B12 every day or every other day during the first week of treatment. The next month, they receive injections every week, subsequently followed by monthly injections. The alternative to intramuscular injection B12 is high-dose oral B12. A 1000 to 2000 mcg/day has been demonstrated to be effective, although recommendations are to always use the parenteral route in severe neurological manifestations. Approved sublingual and intranasal formulations of B12 are also available.[rx][rx] Oral dosage is recommended for patients unable to take IM injections, but cobalamin levels must be measured frequently to ensure absorption. Finally, oral therapy is not recommended for patients with CNS symptoms.
Monitoring
The earliest sign of treatment response is an increase in reticulocyte count, usually within three days of treatment. Following changes in the decrease of biochemical markers such as MMA and plasma homocysteine levels have been observed in the first five days of treatment. Sustained normalization of serum cobalamin usually occurs following two weeks of therapy.[rx] The macrocytosis correction takes place during the first month of treatment. A clinical interview should be considered every year to monitor for new symptoms. These may include epigastric pain, dysphagia, iron deficiency, and/or others that can require gastroscopic investigation.
The key management principle is the importance of routine follow-up. Patients with underlying causes like chronic pancreatitis, bacterial overgrowth, or tapeworm will require additional treatments. Blood transfusions are not required in most patients. With treatment, the symptoms of heart failure resolve, but some patients may require concomitant diuretic therapy.
Genetic counseling may be of benefit for people with pernicious anemia and their families.
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