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Insufficient vitamin intake
8%
2/24
Pancreatic insufficiency
0%
0/24
Pernicious anemia
75%
18/24
Overgrowth of intestinal bacterial
Folate deficiency
17%
4/24
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This presentation of megaloblastic anemia and neurologic deficits is consistent with vitamin B12 deficiency. The etiology of vitamin B12 deficiency was historically determined by the Schilling test, which is the test described in this question. The findings described, which is a defect in oral absorption at baseline with correction upon intrinsic factor administration, is pathognomonic of pernicious anemia. Pernicious anemia is an autoimmune condition where the parietal cells in the stomach are damaged. This leads to a defect in the production of intrinsic factor, a necessary cofactor in the oral absorption of vitamin B12, which over time will lead to a vitamin B12 deficiency and the associated symptoms of anemia and neurologic deficits. It is important to note that the signs and symptoms of vitamin B12 deficiency will not manifest for months or years because of the large systemic reserves compared to the amount that is needed for daily maintenance. As presented by Oh et al, the Schilling test was historically used to determine whether oral or intramuscular vitamin B12 supplementation was necessary. The test itself starts with a baseline phase where the patient was loaded with intramuscular Vitamin B12 and then given a radiolabeled vitamin B12 challenge to see if there was absorption. If not, intrinsic factor (to test for pernicious anemia), antibiotics (to test for bacterial overgrowth), and pancreatic enzymes (to test for pancreatic insufficiency) were sequentially provided until a response was seen. The paper by Rojas et al. discusses the most current understanding of the mechanism behind pernicious anemia was well as the treatment for the disorder. As they discuss, the current consensus suggests that pernicious anemia is due to an autoimmune response directed against the gastric proton pump given its association with chronic atrophic gastritis. Significantly, they note that a non-intrinsic factor mediated mechanism of B12 absorption was discovered and so currently it is thought that oral and parenteral administration of B12 is equally efficacious. Incorrect Answers: Answer 1: Insufficient intake of vitamin B12 should not show a defect in the first phase of the Schilling test. Answer 2: Pancreatic insufficiency as the mechanism of B12 malabsorption will not correct with the addition of intrinsic factor. Answer 4: Overgrowth of intestinal bacteria would correct with antibiotic administration rather than intrinsic factor administration. Answer 5: Folate deficiency would not present with neurologic deficits and would not show the characteristic Schilling test results described here.
3.5
(4)
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