DDSEP® 8 Quick Quiz

October 2019 - Quick Quiz Question 2

A 65-year-old man with chronic pancreatitis related to long-standing alcohol use comes to see you for a second opinion. He has been abstinent from alcohol for 20 years. He reports a 1-year history of six loose, oily stools per day, but minimal abdominal pain. He was recently found to have vitamin B12 deficiency by his primary care provider.

What is the likely mechanism for this patient's vitamin B12 deficiency? 

Antibodies to intrinsic factor

Atrophy of gastric lining due to chronic alcohol use

Reduced breakdown of the R-protein by pancreatic proteases

Decreased absorption of vitamin B12 in the ileum due to chronic diarrhea

Loss of vitamin B12 in stool, due to steatorrhea

Q2. Correct answer: C

Rationale
Vitamin B12 absorption requires intrinsic factor to bind B12 to facilitate absorption in the terminal ileum. Any interruption of terminal ileal absorptive capacity can thus lead to vitamin B12 deficiency (e.g. Crohn's disease, ileal resection). Intrinsic factor is produced by parietal cells, so any condition that leads to decreased parietal cell mass or function can lead to vitamin B12 deficiency (e.g. atrophic gastritis). In order for intrinsic factor to bind vitamin B12, B12 must first be released from binding with the R-protein, which occurs via pancreatic protease breakdown of the R-protein. Patients with chronic pancreatitis are not able to break down the R-protein as efficiently, and thus can develop vitamin B12 deficiency.

References
1. Green R. Vitamin B12 deficiency from the perspective of a practicing hematologist. Blood. 2017;129(19):2603-11.

2. Gueant GL, at al. Malabsorption of vitamin B12 in pancreatic insufficiency of the adult and of the child. Pancreas 1990 Sep;5(5):559-67.

ginews@gastro.org

Next Article: