MD Gastrointestinal Tract Disorders 4

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?

Accepted Answer

APC/Wnt pathway (chromosomal instability)

Answer

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?

Accepted Answer

Familial adenomatous polyposis

Answer

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?

Accepted Answer

Hemolytic uremic syndrome

Answer

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?

Accepted Answer

Metronidazole or vancomycin (oral)

Answer

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?

Accepted Answer

Accumulation of nitrogenous waste products impairing cerebral function

Answer

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.

MD - Doctor of Medicine Practice Test

MD - Doctor of Medicine Practice Test

MD Gastrointestinal Tract Disorders 4