A 28-year-old woman reports intermittent constipation followed by diarrhea and abdominal pain relieved by defecation. What is the most likely diagnosis?

The presentation of intermittent constipation followed by diarrhea and abdominal pain relieved by defecation is characteristic of irritable bowel syndrome (IBS). IBS is a functional gastrointestinal disorder marked by a combination of symptoms, including altered bowel habits (such as alternating between constipation and diarrhea), abdominal discomfort, and relief of symptoms after bowel movements.

In this scenario, the woman's symptoms align with the hallmark features of IBS, particularly the cyclic nature of her bowel habits and the relief from pain associated with defecation. This reflects the underlying pathophysiology of IBS, where visceral hypersensitivity and altered gastrointestinal motility play significant roles.

Other conditions listed do not fit as well with this symptom pattern. For instance, cholecystitis typically presents with right upper quadrant pain, especially after eating fatty meals, and does not exhibit the characteristic alternating bowel habits. A duodenal ulcer generally causes epigastric pain, often related to meal timing, but does not cause the cyclic nature of bowel symptoms seen in this case. Crohn's disease may present with diarrhea and abdominal pain but is usually associated with more severe symptoms and signs, such as weight loss, fever, or blood in stool, and does not typically manifest as alternating constipation and diarrhea relieved by defec