10 USMLE Gastroenterology Questions with Answers and Explanations (Set 2)

These 10 USMLE gastroenterology practice questions (Set 2) cover diarrhea mechanisms, portal hypertension, dysphagia work-up, rectal bleeding, pancreatitis, gastroparesis, infections in AIDS and carcinoid syndrome. Each question includes the correct answer and an explanation.

Written by Dr. Ray Makar, MD, author of the Repeated USMLE Questions eBook series.

Prefer video? Watch daily USMLE case questions on MedFocus by Dr. Ray on YouTube.

How to use this page: read the question, pick your answer, then tap Show Answer and Explanation.

Questions

Question 1. A 23-year-old man presents to the emergency room complaining of massive watery diarrhea for 6 hours. He doesn’t have any vomiting or abdominal pain. Stool culture reveals a curved, Gram-negative rod that secretes an enterotoxin containing subunit A and a binding subunit B. What is the most likely reason for this patient’s massive diarrhea?

A- Deficiency in the brush border enzymes
B- Decreased production of cAMP
C- Increased production of cAMP
D- Destruction of the absorptive epithelium
E- Increased motility of the small intestine

This patient most likely presents with cholera. Cholera enterotoxin causes secretory diarrhea, which means that excretion of water exceeds to a large extent its absorption. The enterotoxin indirectly stimulates adenylate cyclase to produce cAMP, which results in increased intracellular concentration of cyclic AMP which causes prolonged opening of the chloride channels leading to massive excretion of water.
The correct answer is C

 

Question 2. A 55-year-old man with a long history of liver cirrhosis visits his physician with a new complaint. Recently he noticed abnormal lesion on his abdomen. His physician recognized these lesions as caput medusae. Which veins are most likely involved in this case?

A- Azygos and hemiazygos veins
B- Esophageal venous plexus
C- Paraumbilical and epigastric veins
D- Superior, middle and inferior rectal veins
E- Splenic and external iliac veins

Caput medusae is formed by dilated veins seen on the abdomen of patients with liver cirrhosis due to portal hypertension. It is mainly caused by dilation of paracaval connections between paraumbilical veins and epigastric veins.
The correct answer is C

 

Question 3. A 48-year-old woman presents to the clinic for a complaint of difficult swallowing solid food for the last 2 months. After seconds of swallowing, she feels the food getting stuck at the suprasternal notch. She has no history of food or acid regurgitation. She has not lost weight. She does not smoke or drink alcohol. Her medical, surgical and family histories are unremarkable. Her physical examination and laboratory investigations are normal. What is the best next step of management?

A- Barium swallow
B- CT body screening
C- Esophageal manometry
D- Trial of proton pump inhibitor
E- Upper endoscopy

Dysphagia after seconds of swallowing suggests esophageal reason. The most common cause of esophageal dysphagia is esophageal reflux disease, motility disorder or stricture formation. Esophageal cancer can cause the same type of dysphagia so; it should be excluded by upper endoscopy. Barium swallow should follow if there is any stricture or gross lesion. Manometry is recommended is cases of achalasia which is not expected for this case as it eventually leads to dysphagia of solids and liquids.
The correct answer is E

 

Question 4. A 43-year-old man visits his physician concerned about finding traces of bright red blood on toilet paper after he wipes. His stool has normal color and not mixed with blood. His medical and surgical histories are unremarkable. He has no family history of colon cancer. What is the most appropriate next step in management?

A- Anoscopy
B- Barium enema
C- Colonoscopy
D- Fecal occult blood test
E- Sigmoidoscopy

This is a case of scant hematochezia which is characterized by a few drops of bright red blood on toilet paper after defecation. It is not stools mixed with blood. Anoscopy or proctoscopy is the appropriate next step to evaluate the anal canal for hemorrhoids, fissures, polyps, ulcers or tumors. Other tests are used in older age, stool mixed with blood or dark-colored stool.
The correct answer is A

 

Question 5. A 51-year-old man is brought to the emergency room because of severe abdominal pain which is radiating to his back. Today, the patient had many episodes of vomiting. He is an alcoholic, drinking daily but he does not smoke or take any recreational drugs. On physical examination, the patient is lying down in the fetal position and appearing to be ill and febrile. There is also an area of bluish periumbilical discoloration on the skin of his abdomen. However, there is no flank discoloration. There are also reduced bowel sounds and he is having severe mid epigastric tenderness on palpation. The rectal examination is normal. What is your primary diagnosis?

A- Appendicitis
B- Pyelonephritis
C- Necrotizing pancreatitis
D- Acute cholecystitis

Necrotizing pancreatitis is a condition where acute pancreatitis develops severe complications. The pancreas becomes inflamed, leaking its enzymes into the other parts of the pancreas. These enzymes can cause the death of the pancreatic tissue, thus causing necrotizing pancreatitis. Once the dead tissue becomes infected, it can lead to life-threatening complications. Treatment starts with supportive care: IV fluids, pain control and nutrition. Removal of dead tissue (necrosectomy) is delayed and done only if the necrosis becomes infected or symptoms persist. Cullen sign (periumbilical bruising) reflects bleeding into the retroperitoneum.
The correct answer is C

 

Question 6. A 62-year-old woman with a history of type 2 diabetes complains of nausea and bloating for the last three months. Gastric emptying studies confirm the diagnosis of diabetic gastroparesis. What is the first line therapy for this patient?

A- Clindamycin
B- Metoclopramide
C- Omeprazole
D- Ondansetron
E- Sodium bicarbonate

Diabetic gastroparesis is characterized by delayed stomach emptying which leads to nausea and bloating following meals. A prokinetic (promotility) drug such as metoclopramide helps in emptying of the stomach and improving her symptoms. Other choices have no role in esophageal or gastric motility.
The correct answer is B

 

Question 7. A 32-year-old man with a history of HIV infection presents to the clinic complaining of fecal urgency and bloody diarrhea. The patient was diagnosed with pneumocystis jiroveci pneumonia 6 months ago. Which of these organisms is the most likely involved in this condition?

A- Clostridium difficile
B- cytomegalovirus
C- Entamoeba histolytica
D- Giardia lamblia

Fecal urgency and bloody diarrhea suggests cytomegalovirus colitis which is common in patients with AIDS. This infection results in deep ulcers and bleeding. It also causes retinitis, gastritis, pneumonia, hepatitis and encephalitis. Treatment is ganciclovir in addition to antiretroviral therapy.
The correct answer is B

 

Question 8. A 37-year-old woman complains of watery diarrhea, abdominal cramps and periodic facial flushing for the last six months. Examination reveals bilateral wheezing and slightly enlarged liver. Urine analysis shows high levels of 5-hydroxyindoleacetic acid (5-HIAA). Multiple tumors are detected by a CT scan. What is the most likely primary site of these tumors?

A- Colon
B- Esophagus
C- Small Intestine
D- Stomach

This is a typical presentation of carcinoid tumors which arise from the neuroendocrine cells. The most common site of these tumors is the small intestine (50%). Other less common sites are the colon and the tip of the appendix. They secrete serotonin and histamine which are responsible for these symptoms. Serotonin secreted by these tumors is inactivated to 5-HIAA by the liver which excreted in urine. When the tumors spread to the liver, the secretion of serotonin bypass the inactivation of it resulting in carcinoid syndrome which is featured in this patient.
The correct answer is C

 

Question 9. A 26-year-old man presents to the clinic with a complaint of recurrent episodes of bloating, flatulence and diarrhea following eating dairy products. He mentions that he does not experience these symptoms if he does not drink milk or if he is fasting. What is the most likely cause of diarrhea in this patient?

A- Inflammatory
B- Osmotic
C- Psychogenic
D- Secretory

These symptoms indicate lactase insufficiency, known as lactose intolerance. Presence of non-absorbable osmotically active substance such as lactose in the intestinal lumen leads to osmotic diarrhea. Osmotic diarrhea also occurs after ingestion of magnesium-containing laxatives as Milk of Magnesium. Other types of diarrhea do not subside after fasting or avoiding dairy products which confirm the diagnosis of lactose intolerance.
The correct answer is B

 

Question 10. A 58-year-old woman is brought to the emergency room complaining of lightheadedness for 4 hours. She has diarrhea with loose stool for 2 days. She explains her symptoms as the flu, and she drinks lots of water as her neighbor advised her to avoid dehydration. Her physician told her that she should take a combined solution of sodium chloride (NaCl) and glucose to prevent dehydration. What is the mechanism of action of this mixture to improve dehydration?

A- It reduces bowel contractions and consequently improves diarrhea
B- Glucose provides energy for NaCl to increase gastric emptiness
C- The mixture helps to increase the secretion of water and Na through the large intestine
D- Cotransport of glucose and NaCl across the intestinal membrane facilitates the absorption of water and Na.

The combined glucose–NaCl solution works through the sodium–glucose cotransporter (SGLT-1) in the small intestine.
Glucose and sodium are absorbed together across the intestinal epithelium.
This cotransport creates an osmotic gradient that pulls water along with sodium into the bloodstream.
Importantly, this mechanism remains functional even during diarrhea, which is why oral rehydration therapy is effective.
Why the other options are incorrect:
A: It does not reduce bowel contractions.
B: Glucose does not provide energy to increase gastric emptying.
C: The goal is absorption, not secretion, of water and sodium.
The correct answer is D

 

High-yield points from this set

  • Cholera toxin raises cAMP in intestinal cells and causes massive secretory diarrhea.
  • Caput medusae = dilated paraumbilical veins draining into epigastric veins in portal hypertension.
  • Dysphagia to solids without weight loss: start with a barium swallow or endoscopy.
  • A few drops of bright red blood on the toilet paper in a younger adult: start with anoscopy.
  • Cullen sign (periumbilical bruising) suggests hemorrhagic or necrotizing pancreatitis.
  • Diabetic gastroparesis: metoclopramide is a first-line prokinetic.
  • Bloody diarrhea in advanced AIDS = CMV colitis.
  • Flushing, diarrhea, wheezing and high urine 5-HIAA = carcinoid syndrome, usually from the small intestine with liver metastases.
  • Diarrhea only after dairy that stops with fasting = osmotic diarrhea (lactose intolerance).
  • Oral rehydration works through sodium-glucose cotransport (SGLT1) in the small intestine.

Keep practicing

Leave a Comment