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 are classic for IBS. The onset after a stressful event (birthday party with excessive alcohol and food) and the improvement when the patient returned to their hometown also support this diagnosis. The patient's reaction to high FODMAP foods further points towards IBS.
• Other Likely diagnoses:
  • Post-Infectious IBS (PI-IBS): Although the stool tests did not show any infection, it's possible that the patient had a viral or bacterial infection that was not detected, leading to the development of IBS symptoms. The patient's history of having some urge and gas during stressful periods (10&12 board exams) but not having persistent issues until after the birthday party suggests a potential trigger.
  • Functional Dyspepsia: The patient's symptoms of stomach upset, especially after eating certain foods, could also suggest functional dyspepsia. However, the predominant symptoms of bowel habit changes and gas point more towards IBS.
• Do Not Miss diagnoses:
  • Inflammatory Bowel Disease (IBD): Although less likely given the negative stool tests and lack of other symptoms like blood in stool or significant weight loss, IBD (Crohn's disease or ulcerative colitis) must be considered due to its potential severity and the need for specific treatment.
  • Celiac Disease: This autoimmune disorder can cause similar gastrointestinal symptoms and must be ruled out, especially if the patient notices significant improvement on a gluten-free diet.
  • Gastrointestinal Obstruction or Other Mechanical Issues: Although unlikely given the chronic nature of the symptoms and the lack of severe abdominal pain or vomiting, any condition causing a mechanical obstruction or other structural issues in the GI tract could potentially cause similar symptoms.
• Rare diagnoses:
  • Small Intestine Bacterial Overgrowth (SIBO): This condition, characterized by an excessive growth of bacteria in the small intestine, can cause bloating, gas, diarrhea, and abdominal pain, similar to IBS. However, it's less common and typically requires specific testing for diagnosis.
  • Carbohydrate Malabsorption (e.g., fructose or lactose malabsorption): These conditions could explain some of the patient's symptoms, especially if they notice that certain types of carbohydrates trigger their symptoms. However, the patient's reaction to a broad range of foods, including high FODMAP foods, makes IBS a more likely diagnosis.