IBD Knowledge 4 — Questions and Answers
Question 1: What is the significance of the 'string sign' seen on barium follow-through in Crohn's disease?
- It indicates active mucosal bleeding
- It represents severe luminal narrowing due to stricture or spasm (Correct answer)
- It confirms the presence of a fistula
- It shows colonic dilation
Correct answer: It represents severe luminal narrowing due to stricture or spasm
The string sign on barium studies indicates severe narrowing of the terminal ileum from stricture or intense spasm, a classic radiologic finding in Crohn's disease.
Question 2: Which of the following best describes the mechanism of corticosteroid resistance in IBD?
- Increased drug metabolism by gut bacteria
- Overexpression of MDR1 p-glycoprotein effluxing steroids from cells (Correct answer)
- Antibody formation against corticosteroids
- Reduced intestinal absorption due to mucosal damage
Correct answer: Overexpression of MDR1 p-glycoprotein effluxing steroids from cells
Overexpression of MDR1 (multidrug resistance gene 1) encodes p-glycoprotein, which pumps glucocorticoids out of target cells, reducing their anti-inflammatory effect.
Question 3: In UC, what does the term 'backwash ileitis' describe?
- Crohn's disease involving the ileum
- Inflammation of the terminal ileum due to reflux from a severely inflamed colon (Correct answer)
- Ileitis caused by NSAID use
- Post-surgical inflammation at an ileocolic anastomosis
Correct answer: Inflammation of the terminal ileum due to reflux from a severely inflamed colon
Backwash ileitis occurs in ~17% of pancolitis UC patients when colonic contents and inflammation 'wash back' into the terminal ileum through an incompetent ileocecal valve.
Question 4: Which genetic variant in the NOD2 gene confers the highest risk for Crohn's disease?
- NOD2 3020insC frameshift mutation (Correct answer)
- NOD2 promoter methylation
- NOD2 copy number variation
- NOD2 splice site variant
Correct answer: NOD2 3020insC frameshift mutation
The NOD2 3020insC frameshift mutation (Leu1007fsinsC) produces a truncated, nonfunctional protein and is the variant most strongly associated with ileal Crohn's disease.
Question 5: What is 'pouchitis' and which IBD surgery predisposes patients to it?
- Inflammation of the remaining colon after partial colectomy in UC
- Inflammation of the ileal pouch after IPAA surgery for UC (Correct answer)
- Post-surgical infection after ileostomy in Crohn's disease
- Diversion proctitis after loop ileostomy
Correct answer: Inflammation of the ileal pouch after IPAA surgery for UC
Pouchitis is inflammation of the ileal reservoir (J-pouch) created during IPAA surgery for UC, occurring in up to 50% of patients within 10 years.
Question 6: Fecal calprotectin is primarily useful in IBD management for which purpose?
- Diagnosing IBD versus celiac disease
- Distinguishing IBD flare from IBS-like symptoms and monitoring mucosal inflammation (Correct answer)
- Predicting response to biologic therapy
- Screening for colorectal cancer in IBD
Correct answer: Distinguishing IBD flare from IBS-like symptoms and monitoring mucosal inflammation
Fecal calprotectin, a protein released by intestinal neutrophils, correlates with mucosal inflammation and helps distinguish active IBD from functional symptoms or IBS.
Question 7: Which of the following best explains why methotrexate is preferred over azathioprine for Crohn's disease in some patients?
- Methotrexate has fewer drug interactions
- Methotrexate has proven efficacy for inducing remission in Crohn's; azathioprine has not (Correct answer)
- Methotrexate can be used in pregnancy
- Methotrexate does not require laboratory monitoring
Correct answer: Methotrexate has proven efficacy for inducing remission in Crohn's; azathioprine has not
Unlike azathioprine (used for maintenance), methotrexate has demonstrated efficacy in both inducing and maintaining remission in active Crohn's disease in clinical trials.
IBD Knowledge 4
What is the significance of the 'string sign' seen on barium follow-through in Crohn's disease?