Differential Diagnosis

• Single most likely diagnosis
  • Irritable Bowel Syndrome (IBS): Given the patient's history of abdominal symptoms such as diarrhea, gassiness, and urges that started after a stressful event (board exams) and were exacerbated by consumption of junk food and alcohol, IBS is a strong consideration. The fact that symptoms persisted despite a normal stool test and the absence of an identifiable infection supports this diagnosis.
• Other Likely diagnoses
  • Post-Infectious Irritable Bowel Syndrome (PI-IBS): Although the patient mentions not knowing if there was an infection initially, the onset of symptoms after consuming potentially contaminated food (junk food and alcohol) could suggest a possible infectious trigger that led to IBS-like symptoms. The lack of evidence of an ongoing infection does not rule out PI-IBS entirely.
  • Functional Dyspepsia: This condition involves recurring signs and symptoms of indigestion that have no obvious cause. Given the patient's history of gassiness and urges, especially after consuming certain foods, functional dyspepsia could be considered, especially if the patient experiences upper gastrointestinal symptoms like bloating or discomfort.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can present with chronic diarrhea, abdominal pain, and weight loss. Although less likely given the acute onset and lack of systemic symptoms, missing IBD could lead to significant morbidity and mortality if not treated promptly.
  • Celiac Disease: An autoimmune reaction to gluten can cause chronic diarrhea, abdominal pain, and malabsorption. This condition is critical to diagnose as untreated celiac disease can lead to complications like malnutrition and increased risk of certain cancers.
  • Giardiasis or Other Parasitic Infections: Despite the initial stool test being negative, the possibility of a parasitic infection cannot be entirely ruled out without further testing, especially if the patient's symptoms persist. Giardiasis, for example, can cause chronic diarrhea and abdominal cramps.
• Rare diagnoses
  • Microscopic Colitis: This condition involves inflammation of the colon that can only be seen with a microscope. It can cause chronic, watery diarrhea, and is more common in older adults but should be considered in anyone with persistent diarrhea without an obvious cause.
  • Bile Acid Diarrhea: This condition occurs when the body produces too much bile acid or the bile acids are not absorbed properly, leading to chronic diarrhea. It's a less common cause of diarrhea but should be considered in the differential diagnosis of chronic diarrhea.