🧠 GI SYSTEM MIND MAP (NBME Medicine Shelf)

1. Presenting Symptom: Abdominal Pain

• Differentials:

  • RUQ Pain

    • Cholecystitis → RUQ US

    • Choledocholithiasis → RUQ US ± MRCP

    • Cholangitis → RUQ US + Blood Cultures

    • Hepatitis → LFTs, Viral Hep Panel

  • Epigastric Pain

    • Pancreatitis → Lipase, Abdominal CT

    • Peptic Ulcer Disease → H. pylori Testing, EGD

    • GERD → Trial of PPI, ± EGD if alarm symptoms

  • RLQ Pain

    • Appendicitis → CT Abdomen (adults), US (kids)

    • Crohn’s Disease → Colonoscopy ± Biopsy

    • Ovarian Torsion (females) → Pelvic US with Doppler

  • LLQ Pain

    • Diverticulitis → CT Abdomen/Pelvis with contrast

    • Sigmoid Volvulus → Abdominal X-ray (coffee-bean sign), CT

  • Diffuse Pain

    • Bowel Obstruction → Upright Abdomen X-ray

    • Mesenteric Ischemia → CTA Abdomen

    • Gastroenteritis → Stool Studies (if severe)

2. Presenting Symptom: Diarrhea

• Differentials:

  • Acute Watery Diarrhea

    • Viral Gastroenteritis → Clinical

    • Food Poisoning (E. coli, Salmonella, Shigella) → Stool Cultures

  • Bloody Diarrhea

    • Dysentery (Shigella, EHEC) → Stool Culture, Shiga Toxin Assay

    • IBD (Ulcerative Colitis, Crohn’s) → Colonoscopy + Biopsy

  • Chronic Diarrhea

    • Celiac Disease → tTG-IgA antibodies, Duodenal Biopsy

    • IBS → Diagnosis of exclusion

    • Microscopic Colitis → Colonoscopy + Random Biopsies

3. Presenting Symptom: GI Bleed

• Differentials:

  • Upper GI Bleed (Melena, Hematemesis)

    • Peptic Ulcer Disease → EGD

    • Esophageal Varices → EGD

    • Mallory-Weiss Tear → EGD

  • Lower GI Bleed (Hematochezia)

    • Diverticulosis → Colonoscopy

    • Angiodysplasia → Colonoscopy

    • Colorectal Cancer → Colonoscopy + Biopsy

4. Presenting Symptom: Jaundice

• Differentials:

  • Pre-hepatic

    • Hemolysis (e.g., G6PD Deficiency) → CBC, Reticulocyte count, LDH, Haptoglobin

  • Hepatic

    • Viral Hepatitis → Hepatitis Panel

    • Alcoholic Hepatitis → AST>ALT (2:1), Elevated GGT

    • Drug-induced liver injury → Medication history + LFTs

  • Post-hepatic (Obstructive)

    • Gallstones → RUQ US

    • Malignancy (e.g., pancreatic cancer) → CT Abdomen

5. Presenting Symptom: Nausea/Vomiting

• Differentials:

  • Gastroenteritis → Clinical

  • SBO (Small Bowel Obstruction) → Abdominal X-ray

  • Gastric Outlet Obstruction → Abdominal CT, EGD

  • Increased Intracranial Pressure → Head CT/MRI (if neurologic signs)

📝 QUICK STRATEGY TIPS:

• Always start with RUQ Ultrasound for biliary issues.

• CT Abdomen is a key test for acute abdominal pain when diagnosis unclear.

• Endoscopy (EGD or Colonoscopy) is confirmatory for bleeds and chronic diarrhea.

• Labs (LFTs, Lipase, CBC) are first line when systemic signs are present (fever, jaundice).