MD Gastrointestinal Tract Disorders 4 — Questions and Answers
Question 1: A 65-year-old man presents with change in bowel habits, hematochezia, and a 15-pound weight loss over 3 months. Colonoscopy reveals a mass in the sigmoid colon. Which molecular pathway is most commonly altered in sporadic colorectal cancer?
- Microsatellite instability pathway (MMR deficiency)
- APC/Wnt pathway (chromosomal instability) (Correct answer)
- BRAF mutation pathway
- TGF-β signaling pathway
Correct answer: APC/Wnt pathway (chromosomal instability)
The chromosomal instability pathway involving APC tumor suppressor gene mutation is the most common pathway in sporadic colorectal cancer, driving the adenoma-carcinoma sequence.
Question 2: A 30-year-old woman has hundreds of colonic polyps discovered on colonoscopy. Her father died of colon cancer at age 40. Genetic testing reveals an APC gene mutation. She is at greatest risk for which condition?
- Lynch syndrome
- Familial adenomatous polyposis (Correct answer)
- Peutz-Jeghers syndrome
- Juvenile polyposis syndrome
Correct answer: Familial adenomatous polyposis
Familial adenomatous polyposis (FAP) is caused by germline APC mutations, producing hundreds to thousands of adenomatous polyps with nearly 100% lifetime colorectal cancer risk if untreated.
Question 3: A 25-year-old presents with bloody diarrhea 4 days after attending a barbecue. Stool culture grows E. coli O157:H7. Which complication is most feared in this patient?
- Toxic megacolon
- Hemolytic uremic syndrome (Correct answer)
- Pseudomembranous colitis
- Intussusception
Correct answer: Hemolytic uremic syndrome
E. coli O157:H7 produces Shiga toxin that damages renal endothelium, causing hemolytic uremic syndrome characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure.
Question 4: A patient develops severe abdominal pain, fever, and watery diarrhea 5 days after completing a course of clindamycin. Colonoscopy shows yellowish plaques on the colonic mucosa. What is the treatment of choice?
- Metronidazole or vancomycin (oral) (Correct answer)
- Ciprofloxacin
- Ampicillin-sulbactam
- Rifaximin
Correct answer: Metronidazole or vancomycin (oral)
Clostridioides difficile colitis (pseudomembranous colitis) is treated with oral metronidazole for mild-moderate disease or oral vancomycin for severe disease, with fidaxomicin as an alternative.
Question 5: A 55-year-old man with alcoholic cirrhosis develops sudden onset confusion, asterixis, and somnolence. Ammonia level is elevated. Which mechanism best explains hepatic encephalopathy?
- Direct ethanol neurotoxicity
- Cerebral edema from hyponatremia
- Accumulation of nitrogenous waste products impairing cerebral function (Correct answer)
- Hypoglycemia from impaired gluconeogenesis
Correct answer: Accumulation of nitrogenous waste products impairing cerebral function
Hepatic encephalopathy results from the failing liver's inability to detoxify ammonia and other nitrogenous compounds derived from gut bacteria and protein metabolism, causing neurological dysfunction.
Question 6: A 45-year-old obese woman presents with recurrent right upper quadrant pain after meals. Ultrasound shows a thickened gallbladder wall with a stone impacted in the neck. She develops fever and rigors. What is the diagnosis?
- Biliary colic
- Acute cholecystitis (Correct answer)
- Choledocholithiasis
- Ascending cholangitis
Correct answer: Acute cholecystitis
Acute cholecystitis results from cystic duct obstruction by a gallstone, causing gallbladder wall inflammation, distension, and secondary bacterial infection presenting with fever and Murphy's sign.
Question 7: A 68-year-old man with painless jaundice, clay-colored stools, and a palpable, non-tender gallbladder is most likely to have which diagnosis?
- Choledocholithiasis
- Primary sclerosing cholangitis
- Carcinoma of the head of the pancreas (Correct answer)
- Acute cholecystitis
Correct answer: Carcinoma of the head of the pancreas
Painless jaundice with a palpable, non-tender gallbladder (Courvoisier's sign) strongly suggests malignant biliary obstruction, most commonly pancreatic head carcinoma.
MD Gastrointestinal Tract Disorders 4
A 65-year-old man presents with change in bowel habits, hematochezia, and a 15-pound weight loss over 3 months.
Colonoscopy reveals a mass in the sigmoid colon.
Which molecular pathway is most commonly altered in sporadic colorectal cancer?