Gastroenterology (Git) — L6: Acid Related Disorders & Peptic Ulcer

📚 Lecture Overview

This lecture covers acid-related disorders with a primary focus on peptic ulcer disease (PUD), detailing its pathogenesis, clinical presentation, complications, and evidence-based treatments. It also examines the critical role of Helicobacter pylori infection and Zollinger-Ellison syndrome in gastric acid hypersecretion. Mastering these concepts is essential for understanding clinical gastroenterology, pharmacology of acid suppression, and the management of acute abdominal emergencies.

🎯 Key Concepts & Definitions

Peptic Ulcer: A break in the gastric or duodenal mucosa extending through the muscularis mucosae, caused by an imbalance between mucosal defenses and aggressive luminal factors (acid and pepsin).
Erosion: A small, superficial mucosal lesion that does not extend through the muscularis mucosae.
Helicobacter pylori: A spiral, gram-negative rod residing beneath the gastric mucous layer that drives chronic mucosal inflammation, peptic ulcers, and gastric cancer.
Zollinger-Ellison Syndrome (ZES): A condition caused by gastrin-secreting neuroendocrine tumors (gastrinomas) leading to severe hypergastrinemia, gastric acid hypersecretion, and refractory peptic ulcers.
Gastric Outlet Obstruction: A mechanical or inflammatory blockage of the pylorus or duodenal bulb, typically caused by edema or scarring from peptic ulcers.

📖 Main Content

Acid Secretion Regulation

Gastric acid secretion is controlled by stimulatory and inhibitory regulatory molecules:
- Stimulatory molecules: Acetylcholine (neurotransmitter from enteric neurons), Histamine (paracrine from ECL cells), and Gastrin (hormone from G cells).
- Inhibitory molecules: Somatostatin (acts as a paracrine/hormone from gastric endocrine cells). Other inhibitors include GLP-1, CCK, VIP, leptin, and amylin.

Etiology and Pathogenesis of Peptic Ulcer Disease

The two major causes of PUD are NSAIDs and chronic H. pylori infection.
- Duodenal Ulcers: 70–90% associated with H. pylori. Most common in ages 30–55; incidence is declining.
- Gastric Ulcers: Most common in ages 55–70; linked strongly to NSAIDs and low-dose aspirin. Benign ulcers mostly occur in the antrum (60%) or at the junction of the antrum and body on the lesser curvature.
- NSAID Mechanisms: Traditional nsNSAIDs reversibly inhibit COX-1 and COX-2. Aspirin causes irreversible inhibition of COX-1, COX-2, and platelet aggregation. Coxibs preferentially inhibit COX-2, reducing GI events by up to 50% compared to nsNSAIDs, but doubling the risk of cardiovascular complications.

Clinical Presentation & Diagnostics

Symptoms: Epigastric pain is typically gnawing, dull, aching, or hunger-like. 50% report relief with food/antacids, but nocturnal pain (waking the patient from sleep) is common in duodenal ulcers.
Upper Endoscopy: The procedure of choice for diagnosing duodenal and gastric ulcers. Duodenal ulcers are virtually never malignant and require no biopsy; gastric ulcers require biopsies to rule out malignancy.
Testing for H. pylori: Diagnosed via fecal antigen assay, urea breath testing, or endoscopic biopsy (rapid urease test/histology). PPIs must be withheld for at least 14 days before non-invasive testing to avoid false-negatives.

Complications of Peptic Ulcer Disease

Gastrointestinal Hemorrhage: PUD is the most common cause of upper GI bleeding.
Ulcer Perforation: Occurs in <5% of patients (usually anterior wall). Results in sudden, severe generalized abdominal pain and chemical peritonitis progressing to bacterial peritonitis, sepsis, and shock. Physical exam reveals a rigid, quiet abdomen and rebound tenderness. Abdominal CT shows extraluminal free air. Endoscopy is contraindicated.
Gastric Outlet Obstruction: Caused by edema or scarring of the pylorus/duodenal bulb. Presents with early satiety, vomiting of partially digested food, dehydration, metabolic alkalosis, and hypokalemia. A succussion splash may be heard in the epigastrium.

Helicobacter pylori Infection

Pathophysiology: Spiral, gram-negative rod that causes chronic mucosal inflammation (gastritis) with PMNs and lymphocytes.
Antrum-Predominant Infection: Increases gastrin and acid production, driving a high risk for duodenal ulcers.
Gastric Body-Predominant Infection: Leads to mucosal atrophy, decreased acid, intestinal metaplasia, and increased risk for gastric ulcers and gastric cancer (accounts for 80–89% of non-cardia gastric cancers).
Eradication Therapy: Requires high-dose antisecretory therapy (PPI or P-CAB like vonoprazan) combined with two antibiotics for 14 days. Confirmation of eradication is required >4 weeks post-antibiotics and >2 weeks post-PPI discontinuation.

Zollinger-Ellison Syndrome (Gastrinoma)

Pathology: Gastrin-secreting tumors located mostly within the "gastrinoma triangle" (porta hepatis, pancreatic neck, 3rd portion of duodenum). Over two-thirds are malignant. Can be part of MEN 1 syndrome.
Clinical Findings: Refractory peptic ulcers in unusual locations, severe diarrhea, steatorrhea, and weight loss due to direct intestinal mucosal injury and pancreatic enzyme inactivation.
Diagnosis: Fasting serum gastrin concentration >150 pg/mL off PPI/H2 blockers (diagnostic if >1000 pg/mL with acid hypersecretion). Somatostatin receptor scintigraphy (SRS) and endoscopic ultrasonography (EUS) are used for tumor localization.

📊 Visual Learning

flowchart TD A[Epigastric Pain] --> B{Upper Endoscopy} B --> C[Duodenal Ulcer] B --> D[Gastric Ulcer] C --> E[Test H pylori] D --> F[Biopsy to Rule Out Malignancy] E --> G[14-Day Eradication Therapy] F --> G

mindmap root("Peptic Ulcer Disease") "Etiology" "H pylori Infection" "NSAID Use" "Zollinger-Ellison Syndrome" "Complications" "Gastrointestinal Hemorrhage" "Ulcer Perforation" "Gastric Outlet Obstruction" "Diagnostics" "Upper Endoscopy" "Urea Breath Test" "Fecal Antigen Test"

sequenceDiagram participant P as Patient participant C as Clinician participant L as Lab / Endoscopy P ->> C: Epigastric pain & dyspepsia C ->> L: Order Upper Endoscopy & H pylori Test L ->> C: Confirm Ulcer & Positive H pylori C ->> P: Prescribe PPI plus Dual Antibiotics (14 days) P ->> C: Post-treatment follow-up (>4 weeks)

💡 Important Points to Remember

Major Causes: H. pylori infection and NSAID usage account for the vast majority of peptic ulcer cases.
Diagnosis Gold Standard: Upper endoscopy is the diagnostic procedure of choice for visualizing and biopsying ulcers.
Biopsy Rule: Duodenal ulcers do not require biopsy (almost never malignant), whereas gastric ulcers must be biopsied to rule out malignancy.
Testing Pitfall: Proton pump inhibitors (PPIs) cause false-negative urea breath tests and fecal antigen tests; they must be withheld for 14 days prior to testing.
Medication Interactions: Low-dose aspirin doubles GI bleeding risk; combining aspirin with NSAIDs, coxibs, or antiplatelets drastically increases ulcer complications.
Perforation Sign: Sudden generalized abdominal pain with a rigid, quiet abdomen and free air on CT indicates a perforated ulcer (endoscopy is contraindicated).
Obstruction Sign: Vomiting partially digested food with a succussion splash and metabolic alkalosis indicates gastric outlet obstruction.
ZES Hallmark: Refractory ulcers combined with fasting serum gastrin >1000 pg/mL point to Zollinger-Ellison syndrome (gastrinoma).
Eradication Confirmation: Always confirm H. pylori eradication more than 4 weeks after finishing antibiotics and more than 2 weeks after stopping PPIs.
Cardiovascular vs. GI Risk: Coxibs reduce GI ulcer events compared to nsNSAIDs but carry a twofold increase in cardiovascular complications.

⚠️ Common Exam Questions

The PPI Interruption Trap: Examiners will test if you know when to stop PPIs before an H. pylori breath test. Trap: Testing patients while still on PPIs, leading to false-negatives. (Remember: stop PPIs for 14 days).
Duodenal vs. Gastric Malignancy Risk: MCQs often ask which ulcer type requires a biopsy. Trap: Assuming all ulcers need routine biopsy. Duodenal ulcers are virtually never malignant and do not require biopsy; gastric ulcers do.
Perforation Contraindications: Questions will describe a rigid abdomen with free air and ask for the next diagnostic step. Trap: Choosing upper endoscopy. Endoscopy is strictly contraindicated in perforation due to risk of worsening peritoneal contamination.
ZES Presentation: Vignettes present patients with refractory ulcers and severe diarrhea. Trap: Treating empirically for standard PUD without checking fasting serum gastrin or screening for MEN 1 syndrome.

📝 Quick Review Checklist

I can define peptic ulcer disease and distinguish it from erosions
I understand the regulatory molecules of gastric acid secretion (acetylcholine, histamine, gastrin, somatostatin)
I can list the two major etiologies (H. pylori and NSAIDs) and their pathophysiologic mechanisms
I know the indications and diagnostic methods for detecting H. pylori infection
I can recognize the clinical presentation and management of ulcer complications (perforation, hemorrhage, gastric outlet obstruction)
I know how to diagnose and manage Zollinger-Ellison syndrome (gastrinoma)

📚 Gastroenterology (Git) — L6: Acid Related Disorders & Peptic Ulcer