Differential Diagnosis for Sudden Onset of Symptoms

Given the sudden onset of symptoms without evidence of infection in the stool after 20 days, the differential diagnosis can be organized into the following categories:

• Single Most Likely Diagnosis
  • Irritable Bowel Syndrome (IBS): This is the most likely diagnosis given the sudden onset of symptoms without an identifiable cause such as infection. IBS is a functional gastrointestinal disorder characterized by abdominal pain, bloating, and changes in bowel movements, which can start suddenly.
• Other Likely Diagnoses
  • Post-Infectious IBS (PI-IBS): Although no infection was found, it's possible that the symptoms could be related to a post-infectious cause, especially if the initial infection was viral or if the testing missed the causative agent.
  • Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis could present with similar symptoms. The absence of an infection does not rule out IBD, as these are autoimmune conditions.
• Do Not Miss Diagnoses
  • Gastrointestinal Cancer: Although rare, especially in younger individuals, gastrointestinal cancers (like colon cancer) can present with changes in bowel habits and abdominal pain. It's crucial to rule out these conditions, especially with sudden onset and no clear infectious cause.
  • Ischemic Bowel Disease: Reduced blood flow to the intestines can cause sudden onset of abdominal pain and changes in bowel habits. This condition is more common in older adults or those with vascular disease.
  • Celiac Disease: An autoimmune reaction to gluten can cause sudden onset of gastrointestinal symptoms, including abdominal pain and changes in bowel movements, after ingestion of gluten.
• Rare Diagnoses
  • Microscopic Colitis: A condition characterized by inflammation of the colon that can only be diagnosed by microscopic examination of colon tissue. It presents with chronic, watery diarrhea.
  • Eosinophilic Gastroenteritis: A rare condition involving eosinophilic infiltration of the gastrointestinal tract, which can cause a variety of symptoms including abdominal pain and changes in bowel habits.
  • Giardiasis: Although less likely given the negative stool tests, giardiasis (an infection caused by the Giardia parasite) can sometimes be difficult to diagnose and may require repeated testing or different diagnostic methods.

Each of these diagnoses requires careful consideration of the patient's history, physical examination, and additional diagnostic testing as needed to determine the underlying cause of the symptoms.