A 40-year-old man complains of crampy abdominal pain associated with intermittent loose stools for the last three months. He had been healthy until he developed a week of severe diarrhea while visiting India. He then took metronidazole for a week. The diarrhea was resolving by then but evolved soon afterward into his current symptoms. He finds that eating precipitates his symptoms although his weight is stable. Physical examination is unremarkable. Stool microscopy is negative and labs are unrevealing. Which of the following diagnoses is the most likely explanation for his current symptoms?

Correct Answer: A

Rationale: Postinfectious irritable bowel syndrome is an increasingly recognized form of the disease as several studies have demonstrated that a prior bout of gastroenteritis is found in approximately 10 to $20 \%$ of individuals with IBS. Giardiasis is a common cause of acute infectious diarrhea, and a single stool examination may not be sufficient for the diagnosis, but giardiasis usually resolves within several weeks without becoming a chronic illness and usually clears with metronidazole. Acquired lactose intolerance commonly occurs with intestinal infections but resolves once the infection clears. The onset of Crohn's disease does not typically occur after a bout of gastroenteritis, although intestinal bacteria are thought to fuel inflammation in Crohn's disease and antibiotics, such as ciprofloxacin and metronidazole, are used in the management of the disease.

Correct Answer: A

Rationale: The hepatopulmonary syndrome is characterized by platypnea (difficulty breathing when going from lying to sitting) and orthodeoxia (decreased oxygen saturation upon sitting). It is associated with left-to-right shunting of blood. Alpha-1 antitrypsin deficiency and primary biliary cirrhosis are associated with the parenchymal lung diseases mentioned in B and D.

Correct Answer: B

Rationale: Frequent, small meals help buffer stomach acid and reduce irritation of the ulcer, making it a recommended dietary strategy for PUD management.

Correct Answer: C

Rationale: A balanced diet supports healing, avoids irritants, and maintains overall health, making it the most beneficial lifestyle change for PUD.

Correct Answer: C

Rationale: Avoiding food 3 hours before bedtime reduces nighttime acid production and reflux, aiding PUD management.