Pernicious Anemia
Also known as Addison’s anemia, pernicious anemia is a megaloblastic anemia characterized by decreased gastric production of hydrochloric acid and deficiency of intrinsic factor, a substance normally secreted by the parietal cells of the gastric mucosa that’s essential for vitamin B12 absorption. The resulting deficiency of vitamin B12 causes serious neurologic, psychological, gastric, and intestinal abnormalities. Increasingly fragile cell membranes induce widespread destruction of red blood cells (RBCs), resulting in low hemoglobin levels.
In the United States, pernicious anemia is most common in New England and the Great Lakes region. It’s rare in children, Blacks, and Asians. Onset typically is between ages 50 and 60; incidence rises with increasing age.
Causes
Familial incidence of pernicious anemia suggests a genetic predisposition. This disorder is significantly more common in patients with immunologically related diseases, such as thyroiditis, myxedema, and Graves’ disease.
An inherited autoimmune response may cause gastric mucosal atrophy and consequently decreases hydrochloric acid and intrinsic factor production. Intrinsic factor deficiency impairs vitamin B12 absorption. The resultant vitamin B12 deficiency inhibits the growth of all cells, particularly RBCs, leading to insufficient and deformed RBCs with poor oxygen-carrying capacity.
Pernicious anemia also impairs myelin formation. Initially, it affects the peripheral nerves, but gradually it extends to the spinal cord, causing neurologic dysfunction.
Secondary pernicious anemia can result from partial removal of the stomach, which limits the amount of productive mucosa.
Complications
Patients treated with vitamin B12 injections have few permanent complications. Those who go untreated may experience permanent neurologic disability (including paralysis) and psychotic behavior; they may also lose sphincter control of bowel and bladder, and some eventually may die of the disorder. Although the reason is unclear, the incidence of peptic ulcer disease is four to five times greater in patients with pernicious anemia than in the general population.
Assessment
Although pernicious anemia usually has an insidious onset, the patient’s history may reveal this characteristic triad of symptoms including weakness, a beefy red sore tongue, and numbness and tingling in the extremities. The patient may also complain of nausea, vomiting, anorexia, weight loss, flatulence, diarrhea, and constipation.
On inspection, the tongue appears beefy red and smooth. Slightly jaundiced
sclera and pale to bright-yellow skin may be present with hemolysis-induced hyperbilirubinemia.
sclera and pale to bright-yellow skin may be present with hemolysis-induced hyperbilirubinemia.
Understanding the Schilling test
In the Schilling test—the definitive test for pernicious anemia—the patient receives a small (0.5- to 2-mcg) oral dose of radioactive vitamin B12 after fasting for 12 hours. A larger (1-mg) dose of nonradioactive vitamin B12 is given I.M. 2 hours later as a parenteral flush. Then the radioactivity of a 2-hour urine specimen is measured.
Normally, vitamin B12 is absorbed, and excess amounts—about 9%—are excreted in the urine within 24 hours. However, in pernicious anemia, the vitamin remains unabsorbed, with less than 6% excreted in the urine. When the Schilling test is repeated with intrinsic factor added, the test shows normal excretion of vitamin B12.
The pulse rate is rapid, and auscultation may reveal a systolic murmur. Percussion or palpation may reveal an enlarged liver and spleen.
When neurologic involvement occurs, the patient may complain of weakness in the extremities; peripheral numbness and paresthesia; disturbed position sense; lack of coordination; impaired fine finger movement; light-headedness; headache; altered vision (diplopia, blurred vision), taste, and hearing (tinnitus); loss of bowel and bladder control; and, in males, impotence.
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