Differential Diagnosis for Chronic Diarrhea and Abdominal Pain

Given the history of chronic diarrhea and abdominal pain with a normal USG whole abdomen, the differential diagnoses can be categorized as follows:

• Single Most Likely Diagnosis

  • Irritable Bowel Syndrome (IBS): This is a common condition characterized by chronic abdominal pain and changes in bowel habits, such as diarrhea or constipation, without any visible signs of damage or disease in the digestive tract. The normal USG findings support this diagnosis, as IBS does not typically cause structural abnormalities that would be visible on ultrasound.

• Other Likely Diagnoses

  • Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic diarrhea and abdominal pain. Although the USG is normal, early or mild cases might not show significant abnormalities on ultrasound, necessitating further diagnostic tests like endoscopy or MRI.
  • Lactose Intolerance or Other Food Intolerances: These conditions can lead to chronic diarrhea and abdominal pain after consuming certain foods. The normal USG does not rule out these diagnoses, as they are functional disorders rather than structural ones.
  • Small Intestine Bacterial Overgrowth (SIBO): This condition involves an abnormal increase in the bacteria that inhabit the small intestine, leading to symptoms like diarrhea and abdominal pain. USG would not typically detect SIBO, requiring breath tests or other specific diagnostic methods.

• Do Not Miss Diagnoses

  • Celiac Disease: An autoimmune disorder where the ingestion of gluten leads to damage in the small intestine, causing chronic diarrhea and abdominal pain. It's crucial to diagnose celiac disease due to its potential for long-term complications if left untreated, and USG might not detect the intestinal damage.
  • Colon Cancer: Although less common in younger populations, colon cancer can present with chronic diarrhea and abdominal pain. A normal USG does not rule out this diagnosis, especially if other risk factors are present, necessitating further investigation like colonoscopy.
  • Infectious Causes: Chronic infections such as giardiasis can cause prolonged diarrhea and abdominal pain. These infections might not be evident on USG, requiring stool tests for diagnosis.

• Rare Diagnoses

  • Whipple's Disease: A rare, systemic bacterial infection that can cause chronic diarrhea, abdominal pain, and weight loss. Diagnosis is often delayed due to its rarity and nonspecific symptoms, and USG findings would likely be normal.
  • Tropical Sprue: A rare condition characterized by chronic diarrhea and malabsorption, typically acquired in tropical regions. The diagnosis would require specific tests and consideration of travel history, with USG being non-diagnostic.
  • VIPoma: A rare endocrine tumor that secretes vasoactive intestinal peptide (VIP), leading to severe chronic diarrhea and other symptoms. This condition would not be visible on USG, requiring other diagnostic approaches like CT scans or hormone level tests.