Differential Diagnosis

The patient presents with a long-standing history of diarrhea and stomach upset following a specific meal, with normal test results and a history of occasional urges and gas during stressful periods. Here's a differential diagnosis based on the provided information:

• Single most likely diagnosis

  • Irritable Bowel Syndrome (IBS): This condition is characterized by chronic abdominal pain, bloating, and alteration of bowel habits in the absence of any mechanical, inflammatory, or biochemical abnormalities. The patient's symptoms of long-standing diarrhea, stomach upset, and previous episodes of gas and urges, especially during stressful periods, align with IBS. The normal test results also support this diagnosis, as IBS is a diagnosis of exclusion.

• Other Likely diagnoses

  • Post-Infectious Irritable Bowel Syndrome (PI-IBS): Although the stool test was normal, it's possible that the initial episode of diarrhea was due to an infection that wasn't detected, leading to the development of PI-IBS. The symptoms and normal test results could fit this diagnosis.
  • Functional Dyspepsia: This condition involves recurring signs and symptoms of indigestion that have no obvious cause. The patient's stomach upset could be related to functional dyspepsia, especially if the symptoms are related to eating.
  • Small Intestine Bacterial Overgrowth (SIBO): This condition occurs when there is an abnormal increase in the bacteria in the small intestine, which can cause diarrhea, bloating, and gas. Although less likely without specific test results indicating SIBO, it remains a possibility given the chronic nature of the symptoms.

• 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 and abdominal pain. Although the normal test results make this less likely, missing IBD could have significant consequences, and further evaluation might be necessary to rule it out completely.
  • Celiac Disease: An autoimmune reaction to gluten can cause chronic diarrhea, abdominal pain, and malabsorption. This condition requires a specific test for diagnosis and can have serious long-term consequences if not treated.
  • Giardiasis: A parasitic infection that can cause chronic diarrhea. Although the initial stool test was negative, giardiasis can sometimes be missed and requires specific testing for diagnosis.

• Rare diagnoses

  • Tropical Sprue: A rare condition that affects the small intestine's ability to absorb nutrients, leading to chronic diarrhea and malabsorption. It's typically associated with travel to tropical areas.
  • Whipple's Disease: A rare, systemic bacterial infection that can cause chronic diarrhea, abdominal pain, and malabsorption. It's extremely rare and usually presents with additional systemic symptoms.
  • Lactose or Fructose Malabsorption: Although less likely given the variety of foods consumed before the onset of symptoms, malabsorption of specific sugars can cause chronic diarrhea and gas. Specific tests are required for diagnosis.