Differential Diagnosis

• Single most likely diagnosis:
  • Irritable Bowel Syndrome (IBS): The patient's symptoms of abdominal pain, changes in bowel habits (diarrhea, loose stools), gas, and urgency, especially triggered by high FODMAP foods and stress, are classic for IBS. The onset after a stressful event (birthday party with excessive alcohol and food) and the absence of infectious causes (negative stool tests) further support this diagnosis.
• Other Likely diagnoses:
  • Post-Infectious IBS (PI-IBS): Although the stool tests were negative, the onset of symptoms after a bout of diarrhea (which could have been infectious) suggests the possibility of PI-IBS. The patient's history of having some urge and gas during stressful periods (10&12 board exams) but not to this extent could indicate a predisposition to IBS-like symptoms that were exacerbated by an infectious event.
  • Functional Dyspepsia: Overlapping symptoms with IBS, such as abdominal pain and discomfort, could suggest functional dyspepsia, especially given the trigger of eating certain foods (high FODMAP).
• Do Not Miss diagnoses:
  • Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis could present with chronic diarrhea, abdominal pain, and urgency. Although less likely given the negative tests and the specific triggers (high FODMAP foods, stress), missing IBD could lead to significant morbidity.
  • Celiac Disease: An autoimmune reaction to gluten could cause similar gastrointestinal symptoms. Given the patient's ability to eat almost everything without issues before the birthday event, this is less likely, but it's crucial not to miss due to the availability of a specific treatment (gluten-free diet).
• Rare diagnoses:
  • Small Intestine Bacterial Overgrowth (SIBO): Could present with bloating, gas, and changes in bowel habits, especially after a bout of diarrhea or antibiotic use. The patient's symptoms of gas and loose stools, especially with high FODMAP foods, might suggest SIBO, although it's less common.
  • Fructose Malabsorption: Given the patient's reaction to sugarcane juice (high in fructose) at the birthday party, fructose malabsorption could be considered, though it's less likely given the broader range of triggers (not just fructose-containing foods).