System 03 · ~9% of exam
Gastrointestinal
Abdominal pain is the entry point. Location, character, and associated features organize the differential into upper vs lower, inflammatory vs obstructive vs ischemic vs perforated.
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Chief complaints
BUILD THE DIFFERENTIAL
Vignettes enter through one of these doors. Each complaint lays out the full differential, marks the can't-miss diagnoses, and tells you the next right action for each.
CHIEF COMPLAINT · HIGH-YIELD
Abdominal pain
Location is the first question. Character, radiation, and associated symptoms narrow the list.
Approach
RUQ: cholecystitis, cholangitis, hepatitis, right lower lobe pneumonia. Epigastric: PUD, pancreatitis, MI. RLQ: appendicitis, ovarian torsion, ectopic, nephrolithiasis, Crohn. LLQ: diverticulitis, sigmoid volvulus, ovarian torsion, ectopic. Diffuse: peritonitis, mesenteric ischemia, DKA, SBO/LBO, perforation.
The differential
| Diagnosis | Key features / clues | Next step |
|---|---|---|
| AAA rupture | Older smoker, sudden severe abdominal or back pain, hypotension, pulsatile mass. | Unstable → OR · stable → CT angio |
| Mesenteric ischemia | Pain out of proportion to exam, AFib or vascular disease, bloody diarrhea late. | CT angio · lactate · emergent revascularization or bowel resection |
| Perforated viscus | Sudden severe pain, rigid abdomen, rebound and guarding, free air on upright CXR or CT. | NG tube · IV fluids · broad-spectrum antibiotics · emergent surgery |
| Ectopic pregnancy | Woman of childbearing age, amenorrhea, pelvic pain, hypotension if ruptured. | Urine β-hCG · transvaginal US · methotrexate or surgery |
| Appendicitis | Periumbilical pain migrating to RLQ, anorexia, low-grade fever, McBurney tenderness, Rovsing/psoas/obturator signs. | CT abdomen (US in kids or pregnancy) · appendectomy |
| Cholecystitis | RUQ pain, fever, Murphy sign, postprandial, fatty food trigger. | RUQ US · HIDA if equivocal · cholecystectomy |
| Pancreatitis | Epigastric pain radiating to back, nausea, vomiting. Lipase > 3× upper limit. | Lipase · RUQ US for gallstones · LR IV fluids · pain control · early feeding |
| Diverticulitis | LLQ pain, fever, leukocytosis, older patient. | CT abdomen · uncomplicated: antibiotics outpatient · complicated: IV antibiotics ± drainage or surgery |
| Small bowel obstruction | Crampy, colicky, vomiting, distension, high-pitched then absent bowel sounds. Prior surgery (adhesions) or hernia. | CT abdomen · NG decompression · IV fluids · NPO · surgery if failure, strangulation, closed loop |
⚑ = can't-miss diagnosis · rule out first
Classic vignette
Exam-style stem
A 68-year-old man with AFib (off anticoagulation) presents with severe abdominal pain for 4 hours. Exam is benign except for mild tenderness. Lactate 5.8. WBC 18.
Most likely diagnosis?
Answer › Acute mesenteric ischemia (embolic, likely SMA). Classic: pain out of proportion to exam, AFib risk factor, lactic acidosis. CT angio confirms. Emergent surgical or endovascular revascularization.
Pearls
Pearl
Every woman of reproductive age with abdominal pain gets a pregnancy test. Full stop.
Pearl
Rebound and guarding indicate peritoneal irritation, which is a surgical abdomen. Do not wait for imaging to call surgery.
Pearl
Ranson criteria and BISAP score pancreatitis severity. Imaging to assess severity is not indicated in the first 72 hours, do it later if not improving.
CHIEF COMPLAINT · HIGH-YIELD
GI bleeding
Upper vs lower. Resuscitate first, then localize.
Approach
Upper GI bleed (hematemesis, melena): PUD, varices, Mallory-Weiss, gastritis, malignancy. Lower GI bleed (hematochezia): diverticulosis, angiodysplasia, malignancy, colitis, hemorrhoids. Massive upper GI bleed can present as hematochezia.
The differential
| Diagnosis | Key features / clues | Next step |
|---|---|---|
| Variceal bleed | Known cirrhosis, hematemesis, coffee-ground, hemodynamic instability. | IV octreotide + ceftriaxone + PPI drip · urgent EGD with banding · TIPS if refractory |
| Peptic ulcer bleed | NSAID, H. pylori, alcohol, prior ulcer, melena, hematemesis, epigastric pain. | IV PPI · EGD within 24 hrs · endoscopic therapy for high-risk features · H. pylori testing |
| Aortoenteric fistula | Prior AAA repair, sentinel bleed, later massive bleed. | CT angio · emergent surgery |
| Diverticular bleed | Painless hematochezia in elderly, self-limited in 80%. | Resuscitate · colonoscopy · angiography if active bleeding not localized |
| Mallory-Weiss | Retching → hematemesis. Alcohol use. | Supportive, usually self-limited · EGD if persistent |
⚑ = can't-miss diagnosis · rule out first
Classic vignette
Exam-style stem
A 55-year-old man with cirrhosis presents with hematemesis. BP 85/50, HR 120. Hb 7.2. INR 1.8.
Next steps?
Answer › Resuscitate: two large-bore IVs, type and cross for 4 units pRBCs, transfuse (target Hb 7–9). Start octreotide, ceftriaxone (reduces mortality in variceal bleed by preventing SBP), IV PPI. Urgent EGD for banding within 12 hours.
Pearls
Pearl
Transfuse to Hb 7 in most GI bleeds. Over-transfusion increases portal pressure and rebleeding in variceal bleeds.
Pearl
BUN/Cr ratio > 30 suggests upper GI bleed (digested blood becomes urea).
Pearl
NG lavage is no longer routinely recommended, it does not change outcomes and misses duodenal bleeds.
CHIEF COMPLAINT
Jaundice
Pre-hepatic, hepatic, post-hepatic. The bilirubin fractionation tells you which.
Approach
Unconjugated (indirect) predominates: hemolysis, Gilbert, Crigler-Najjar. Conjugated (direct) predominates: hepatocellular disease (viral hepatitis, alcoholic, drug-induced) or obstruction (stones, stricture, malignancy). Painless jaundice in an older patient is pancreatic head cancer until proven otherwise.
The differential
| Diagnosis | Key features / clues | Next step |
|---|---|---|
| Choledocholithiasis | RUQ pain, jaundice, elevated alk phos and direct bili, dilated CBD on US. | MRCP or EUS · ERCP to remove stones |
| Ascending cholangitis | Charcot triad: fever, jaundice, RUQ pain. Reynolds pentad adds hypotension and AMS. | Blood cultures · broad-spectrum antibiotics · urgent ERCP for decompression |
| Pancreatic head cancer | Painless jaundice, weight loss, Courvoisier sign (palpable non-tender gallbladder), new diabetes. | CT abdomen with pancreatic protocol · CA 19-9 · EUS biopsy |
| Acute viral hepatitis | Malaise, nausea, RUQ pain, transaminases in thousands, risk factors (travel, exposure, IVDU). | Hepatitis panel (A IgM, B surface Ag and core IgM, C Ab with RNA if positive) · supportive care |
| Alcoholic hepatitis | Heavy alcohol use, AST:ALT > 2:1, AST usually < 500, fever, hepatomegaly. | Maddrey discriminant function ≥ 32 → prednisolone 40 mg × 28 days (if no infection, GI bleed, or renal failure) |
| Hemolysis | Indirect hyperbilirubinemia, low haptoglobin, elevated LDH, anemia. | Reticulocyte count · Coombs · peripheral smear |
⚑ = can't-miss diagnosis · rule out first
Pearls
Pearl
Charcot triad = ascending cholangitis. This is a surgical emergency, the bile duct needs decompression within hours.
Pearl
Painless jaundice in an older patient is pancreatic cancer until proven otherwise. Painful jaundice is usually stones.
Pearl
AST:ALT ratio > 2 with AST usually below 500 suggests alcohol. AST and ALT in the thousands with similar ratio is acute viral or drug-induced hepatitis.
CHIEF COMPLAINT
Diarrhea
Acute vs chronic. Inflammatory (fever, blood, WBC) vs non-inflammatory (watery, large volume).
Approach
Acute (< 2 weeks): mostly infectious. Chronic (> 4 weeks): IBS, IBD, celiac, microscopic colitis, malabsorption, endocrine (hyperthyroid, carcinoid, VIPoma). Bloody: Shigella, EHEC, Salmonella, Campylobacter, C. diff, amoeba, IBD.
The differential
| Diagnosis | Key features / clues | Next step |
|---|---|---|
| EHEC (O157:H7) | Bloody diarrhea, undercooked beef, can progress to HUS (triad: thrombocytopenia, AKI, MAHA). | Stool culture · supportive · AVOID antibiotics (increase HUS risk) and antimotility |
| C. difficile | Recent antibiotics or hospitalization, watery or bloody diarrhea, pseudomembranes on colonoscopy. | Stool PCR or toxin · fidaxomicin or vancomycin PO · fecal transplant for recurrence |
| Inflammatory bowel disease | Young patient, bloody diarrhea, weight loss, extraintestinal features, elevated calprotectin. | Colonoscopy with biopsy |
| Celiac disease | Chronic diarrhea, iron deficiency, dermatitis herpetiformis, weight loss. | Anti-tissue transglutaminase IgA (with total IgA level) · confirm with duodenal biopsy |
| Microscopic colitis | Chronic watery diarrhea in older patient, often on NSAIDs/PPIs/SSRIs. Normal colonoscopy appearance. | Random biopsies · budesonide |
| IBS | Chronic cramping abdominal pain improved with defecation, altered bowel habits, no alarm features. | Clinical diagnosis (Rome IV) · dietary modification · antispasmodics · neuromodulators |
⚑ = can't-miss diagnosis · rule out first
Pearls
Pearl
Do not give antibiotics or antimotility agents in suspected EHEC. They increase the risk of hemolytic uremic syndrome.
Pearl
C. difficile risk factors: recent antibiotics (especially fluoroquinolones, clindamycin, cephalosporins), PPI use, hospitalization, age > 65.
Pearl
Chronic diarrhea + iron deficiency anemia + bloating in a young patient should prompt celiac serology. Do not start a gluten-free diet before testing.
✦
Disease deep dives
DEFINITIVE DX
Once you've identified the likely diagnosis from the chief complaint, these pages give you the presentation, workup, management, and exam pearls in depth.
Inflammatory Bowel Disease
UC vs Crohn. Distribution, depth, and complications split them.
Acute Pancreatitis
Gallstones and alcohol account for 70%. Aggressive fluids and early feeding. Stop the opioids if you can.
Cirrhosis
Know the complications: ascites, SBP, variceal bleed, encephalopathy, HCC, hepatorenal syndrome.
DISEASE DEEP DIVE
Inflammatory Bowel Disease
UC vs Crohn. Distribution, depth, and complications split them.
Presentation
UC: bloody diarrhea, tenesmus, continuous from rectum, mucosal inflammation only. Crohn: any site mouth-to-anus (skip lesions, terminal ileum), transmural, fistulas, strictures, perianal disease.
Workup
- Colonoscopy with biopsy. Diagnostic. UC: continuous, mucosal, pseudopolyps. Crohn: skip lesions, cobblestoning, non-caseating granulomas, transmural.
- Labs. CBC (anemia), CRP/ESR, albumin, iron studies, B12 (terminal ileum), stool studies to rule out infection, fecal calprotectin.
- Imaging. CT or MR enterography for Crohn to assess small bowel and look for fistulas/abscesses.
Management
- UC induction. Mild: topical/oral 5-ASA. Moderate-severe: steroids, then biologics (anti-TNF, vedolizumab, ustekinumab, JAK inhibitors).
- UC maintenance. 5-ASA, biologics. Colectomy is curative.
- Crohn induction. Steroids for flares. Biologics (anti-TNF infliximab/adalimumab, ustekinumab, vedolizumab) for moderate-severe.
- Crohn maintenance. Immunomodulators (azathioprine, methotrexate), biologics. Surgery for strictures and fistulas, not curative (recurrence at anastomosis).
- Surveillance. Colonoscopy 8 years after diagnosis, then every 1–2 years. Dysplasia risk is elevated.
Pearls
Pearl
Extraintestinal manifestations: erythema nodosum, pyoderma gangrenosum, uveitis, aphthous ulcers, ankylosing spondylitis, primary sclerosing cholangitis (especially UC).
Pearl
PSC in UC, always screen LFTs. MRCP if abnormal. Increased risk of cholangiocarcinoma and colon cancer.
Pearl
Toxic megacolon in UC flare: dilated colon > 6 cm, fever, tachycardia, peritonitis. Steroids, bowel rest, surgical consult.
Classic vignette
Exam-style stem
A 25-year-old man with 6 weeks of bloody diarrhea, 10 BMs/day, tenesmus, 8 lb weight loss. Colonoscopy: continuous inflammation from rectum to mid-sigmoid, pseudopolyps, mucosal friability.
Answer › Moderate UC, left-sided. Oral 5-ASA plus topical mesalamine. If no response in 2 weeks, escalate to prednisone, then biologic.
DISEASE DEEP DIVE
Acute Pancreatitis
Gallstones and alcohol account for 70%. Aggressive fluids and early feeding. Stop the opioids if you can.
Presentation
Epigastric pain radiating to back, nausea, vomiting. Cullen (periumbilical ecchymosis) and Grey-Turner (flank) are classic but rare and late.
Workup
- Lipase. > 3× upper limit is diagnostic. More specific than amylase.
- RUQ US. First imaging to rule out gallstones.
- CT with contrast. Only if diagnosis uncertain or not improving after 72 hours. Assesses necrosis.
- Labs. Triglycerides, calcium, LFTs. BISAP score or Ranson criteria for severity.
Management
- IV fluids. Lactated Ringer aggressively in the first 24 hours. Goal-directed approach, overly aggressive is linked to worse outcomes.
- Pain control. IV opioids. Minimize if possible (ileus risk).
- Early feeding. Oral diet within 24–48 hours if tolerated. NPO only if severe nausea or vomiting. NG feeding if PO is not tolerated in severe pancreatitis.
- Gallstone pancreatitis. Cholecystectomy during the same admission once resolved. ERCP if cholangitis or persistent biliary obstruction.
- Necrotizing pancreatitis. Antibiotics only if infected necrosis (imipenem). Minimally invasive drainage before open necrosectomy.
Pearls
Pearl
IGETSMASHED: Idiopathic, Gallstones, Ethanol, Trauma, Steroids, Mumps, Autoimmune, Scorpion sting, Hypertriglyceridemia/Hypercalcemia, ERCP, Drugs.
Pearl
A lipase that drops fast is not reassuring. Clinical trajectory matters more than lipase trend.
Pearl
Early CT scan is usually unhelpful. Wait 72 hours if clinically worsening.
Classic vignette
Exam-style stem
A 48-year-old woman with 6 hours of epigastric pain radiating to back, vomiting. Lipase 1200. RUQ US: gallstones, no ductal dilation.
Answer › Gallstone pancreatitis. LR IV fluids, pain control, early feeding. Cholecystectomy once resolved (before discharge).
DISEASE DEEP DIVE
Cirrhosis
Know the complications: ascites, SBP, variceal bleed, encephalopathy, HCC, hepatorenal syndrome.
Presentation
Asymptomatic → decompensated. Stigmata: spider angiomata, palmar erythema, gynecomastia, caput medusae, ascites, jaundice, asterixis.
Workup
- LFTs, albumin, INR, bilirubin. Synthetic function markers. MELD score (bilirubin, INR, creatinine, sodium) for prognosis and transplant listing.
- Etiology workup. Hepatitis B/C serologies, iron studies, ceruloplasmin, alpha-1 antitrypsin, ANA/AMA, autoimmune markers. Alcohol history.
- Imaging. RUQ US with Doppler. Coarse liver, nodular surface, splenomegaly, varices. Alpha-fetoprotein + US every 6 months for HCC screening.
Management
- Ascites. Sodium restriction (< 2 g/d), spironolactone + furosemide (100:40 ratio). Large-volume paracentesis with albumin replacement (> 5 L removed → 6–8 g albumin per L).
- SBP. Ascitic fluid PMN > 250. Ceftriaxone. Prophylaxis with cipro if prior SBP or low ascites protein.
- Variceal prophylaxis. Primary: non-selective beta-blocker (propranolol, nadolol) OR endoscopic banding. Secondary: both.
- Hepatic encephalopathy. Lactulose (goal 3 soft stools per day). Rifaximin for recurrent episodes. Identify precipitants: GI bleed, infection, electrolytes, constipation, sedatives.
- Hepatorenal syndrome. Albumin + midodrine + octreotide (type 2) or terlipressin (type 1, now available in US). Definitive: transplant.
Pearls
Pearl
SAAG ≥ 1.1 means portal hypertension (cirrhosis, HF, Budd-Chiari). SAAG < 1.1 means other causes (malignancy, TB, nephrotic).
Pearl
Every cirrhotic admission: check for SBP with paracentesis. Ammonia level is NOT required for encephalopathy diagnosis (clinical).
Pearl
MELD ≥ 15 triggers transplant evaluation. Exception points for HCC within Milan criteria.
Classic vignette
Exam-style stem
A 54-year-old with alcoholic cirrhosis presents with abdominal distension and confusion. Ascites on exam. Paracentesis: PMN 400.
Answer › SBP plus hepatic encephalopathy. Ceftriaxone + albumin (1.5 g/kg day 1, 1 g/kg day 3 reduces HRS). Lactulose for encephalopathy. Screen for precipitants.