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USMLE Step 3 (Subject) / Gastroenterology (Lesson)
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- Pancreatitis – Prognosis Mortality:- In patients without organ failure: < 1%- In patients with organ failure: ∼ 30% - Higher mortality in patients with biliary pancreatitis than in patients with alcoholic pancreatitis Important predictors of severity:- Age > 55- Gastrointestinal bleeding- Abnormal hematocrit within 48 hours→ Acute hemorrhagic pancreatitis: ↓ Hct→ Third space fluid loss: ↑ Hct- Hypocalcemia and/or hyperglycemia- Inflammatory markers: ↑↑ CRP, ↑ IL-6, ↑ IL-8- Evidence of shock and/or organ failure- ↑ AST, ↑ ALT- ↑ BUN, creatinine- ↑ LDH- ABG: pO2 < 60 mmHg, metabolic acidosis with a base deficit > 4 mmol/L CT findings: pancreatic edema, peripancreatic fluid collection, and/or necrosis of > 33% of the pancreas Amylase and lipase, which are used for the diagnosis of pancreatitis, cannot be used to predict the prognosis! Numerous scoring systems exist (e.g, Ranson criteria) for assessing the severity and predicting the prognosis of acute pancreatitis
- Ranson criteria Estimates mortality of patients with pancreatitis, based on initial and 48-hour lab values. On Admission- WBC > 16k- Age > 55- Glucose >200 mg/dL (>10 mmol/L)- AST > 250- LDH > 350 48 Hours Into Admission:- Hct drop >10% from admission- BUN increase >5 mg/dL (>1.79 mmol/L) from admission- Ca <8 mg/dL (<2 mmol/L) within 48 hours- Arterial pO2 <60 mmHg within 48 hours- Base deficit (24 - HCO3) >4 mg/dL within 48 hours- Fluid needs > 6L within 48 hours
- Angiodysplasia Most commonly located in the right-sided colon (∼ 75%) Episodic bleeding that ceases spontaneously in > 90% of cases Colonoscopy challenging given episodic nature → diagnosis usually requires angiography Associated with advanced age (>60 years), end-stage renal disease, von Willebrand disease, and aortic stenosis
- Indications for stress ulcer prophylaxis Any 1 factor:- Coagulopathy: platelets < 50,000/mm3, INR > 1.5, PTT > 2x normal control- Mechanical ventilation > 48 hours- GI bleeding or ulceration in the last 12 months- Head trauma, spinal cord injury, major burn ≥ 2 factors:- Glucocorticoid therapy- > 1 week ICU stay- Occult bleeding > 6 days- Sepsis
- Toxic megacolon A life-threatening, acute dilation of the colon associated with systemic toxicity Etiology:- Infectious colitis: C. difficile (pseudomembranous colitis), Salmonella, Shigella, Campylobacter infections, Trypanosoma cruzi (Chagas disease), E. histolytica (amebic dysentery) infections- Inflammatory colitis: Ulcerative colitis, Crohn's disease Pathophysiology: colitis (inflammation)→ Colonic accumulation of inflammatory mediators and bacteria → Nitric oxide synthesis → Colonicdilation→ Edema and inflammation of the colonic smooth muscle → Colonic dysmotility → Colonic dilation Clinical findings:- (Bloody) diarrhea and vomiting- Abdominal distention and pain- Signs of sepsis (fever, tachycardia, hypotension) and dehydration- Signs of underlying disease (See Ulcerative colitis, Crohn's disease) Diagnostics:- Laboratory findings: neutrophilic leukocytosis, anemia, ↑ ESR/CRP, hypokalemia - Abdominal x-ray findings → Dilation of the colon (transverse colon diameter > 6 cm)→ Loss of haustration → Multiple air-fluid levels- Contrast enhanced CT scan (oral and IV contrast)→ Confirms x-ray findings→ Rules out mechanical obstruction (e.g., tumor/stricture)→ Can diagnose complications (ischemic bowel segments or perforation peritonitis) - Stool tests for C. difficile toxin: in patients with preceding diarrhea (- Colonoscopy and endoscopy: contraindicated in suspected toxic megacolon due to high risk of perforating the colon Diagnostic criteria:- Radiographic evidence of colonic dilatation- Three of the following: fever (> 101.5°F), tachycardia (> 120 beats/min), leukocytosis (> 10,500/μL), or anemia- One of the following: dehydration, hypotension, altered mental status, or electrolyte disturbance Complications:- Colonic ischemia → Colonic perforation→ Peritonitis - Sepsis and multiorgan dysfunction Treatment:- Conservative treatment:→ Admission to intensive care unit→ Complete bowel rest: NPO→ Nasogastric tube insertion→ IV fluids→ Correction of fluid and electrolyte imbalances→ Broad-spectrum IV antibiotics (e.g., ampicillin, gentamicin, and metronidazole): Oral vancomycin or fidaxomicin for C. difficile colitis→ Rotation techniques: change position frequently to facilitate the evacuation of bowel gas (prone or knee-elbow position)→ Avoid all anticholinergic or narcotic medications→ IV steroids (hydrocortisone, dexamethasone) for inflammatory bowel disease - Surgery:→ Indications: no response to medical management within 24–72 hours; development of complications→ Procedure: subtotal colectomy and end ileostomy
- Inguinal hernia in children Risk factors:- Premature boys- Genitourinary abnormalities (e.g., cryptorchidism) Clinical features:- Asymptomatic groin mass- Reducible- Increases with abdominal pressure Complications:- Incarceration- Bowel ischemia Management:- Asymptomatic: Elective surgery in 1-2 weeks- Immediate surgical repair for incarceration
- Barrett esophagus Pathophysiology: Reflux esophagitis → stomach acid damages squamous epithelium → squamous epithelium becomes replaced by columnar epithelium and goblet cells (intestinal metaplasia, Barrett's metaplasia)- The physiological transformation zone ("Z-line") between squamous and columnar epithelium is shifted upwards Pathology:- Short-segment Barrett's esophagus (< 3 cm of columnar epithelium between Z-line and GEJ)- Long-segment Barrett's esophagus (> 3 cm of columnar epithelium between Z-line and GEJ) → higher cancer risk! Complications: precancerous condition for adenocarcinoma Management and surveillance:- Medical treatment with PPIs- Endoscopy with four-quadrant biopsies at every 2 cm of the suspicious area (salmon colored mucosa)→ If no dysplasia: repeat endoscopy every 3–5 years→ If indefinite for dysplasia: repeat endoscopy with biopsies after 3–6 months of optimized PPI therapy→ If low-grade dysplasia: Endoscopic therapy of mucosal irregularities → Alternatively: surveillance every 12 months with biopsies every 1 cm→ If high-grade dysplasia: endoscopic therapy of mucosal irregularities
- Hepatic adenoma Epidemiology- Benign epithelial liver tumor- Primarily young women on oral contraception Manifestations- Often asymptomatic (incidentally found)- Episodic abdominal pain- Liver function testing usually normal Diagnosis- CT scan with contrast→ Well demarcated with peripheral enhancement Treatment- Asymptomatic & < 5 cm – stop oral contraception- Symptomatic or > 5 cm – surgical resection Complications- Malignant transformation (~10%)- Rupture & hemorrhage
- Opioid-induced constipation – Treatment Peripherally acting µ-opioid receptor antagonist: - Oral naldemedine/subcutaneous methylnaltrexone - Naloxegol
- Weight loss – Pharmacotherpy - Phenteramine/topiramate (monotherapy with phenteramine is associated with re-gain and no long-term benefit) - Orlistat - Buproprion/naltrexone - Liraglutide
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- Clinical manifestations of hereditary hemochromatosis Skin: Hyperpigmentation (bronze diabetes) Musculoskeletal: Arthralgia, arthropathy & chondrocalcinosis Gastrointestinal: Elevated hepatic enzymes with hepatomegaly (early), cirrhosis (late) & increased risk of HCC Endocrine: Diabetes mellitus, secondary hypogonadism & hypothyroidism Cardiac: Restrictive or dilated cardiomyopathy & conduction abnormalities Infections: Increased susceptibility to Listeria, Vibrio vulnificus & Yersinia enterocolitica
- Management of uncomplicated gallstones Gallstones on imaging without symptoms: No treatment necessary Gallstones on imaging with typical biliary colic symptoms: - Acute pain management- Prophylactic cholecystectomy (usually elective)- Possible UDCA in poor surgical candidates or patients refusing surgery Gallstones with atypical symptoms:- Evaluation for other causes- Trial of UDCA; cholecystectomy in patients whose symtpoms improve Typical biliary colic symptoms without gallstones on imaging:- Cholecystokinin-stimulated cholescintigraphy to evaluate for functional gallbladder disorder- Cholecystectomy in patients with low gallbladder ejection
- Stool osmotic gap 290 mOsm/kg - 2 x (stool Na + stool K) < 50: Secretory diarrhea50-125: indeterminate>125: Osmotic diarrhea