Peptic Ulcer Disease

Peptic ulcer disease (PUD) is a breach in the mucosa of the stomach, pylorus, or duodenum that extends through the muscularis mucosae, caused by an imbalance between aggressive factors (acid and pepsin) and protective mechanisms of the gastrointestinal mucosa. Once the most common cause of acute upper gastrointestinal bleeding and a leading indication for gastrointestinal surgery, the incidence and prevalence of PUD have declined dramatically since the 1990s due to widespread use of proton pump inhibitors (PPIs) and effective treatment of Helicobacter pylori infection. Current epidemiology shows an annual incidence of 5-15 cases per 100,000 population in developed countries, with a lifetime prevalence of approximately 5-10%; the disease now predominantly affects elderly patients on nonsteroidal anti-inflammatory drugs (NSAIDs) rather than younger populations with H. pylori gastritis. Understanding PUD remains essential for board certification and clinical practice because bleeding ulcers continue to represent 15-20% of acute upper GI hemorrhage cases, complications can be life-threatening despite modern therapy, and PUD serves as a paradigm for understanding how infectious agents (H. pylori) and medications (NSAIDs) disrupt mucosal homeostasis.

The development of peptic ulcers results from disruption of the delicate balance between aggressive factors that damage the mucosa and defensive mechanisms that maintain mucosal integrity. Understanding this pathophysiology requires examination of both the etiology-specific mechanisms and the final common pathway of mucosal erosion.

The stomach and duodenum are protected from autodigestion by multiple overlapping defensive mechanisms collectively termed the "mucus-bicarbonate layer." Specialized mucus-secreting cells (primarily mucus neck cells in the stomach and Brunner's glands in the duodenum) produce a viscoelastic mucus composed of glycoproteins (mucins), lipids, and water that forms a gel layer 1-1.5 mm thick adhering to the epithelial surface. Simultaneously, HCO3−-secreting cells in these same regions pump bicarbonate ions into the mucus layer, creating a pH gradient where the mucus surface may be neutral to slightly alkaline (pH 6-7) despite the acidic lumen (pH 1-2). This remarkable phenomenon occurs because the bicarbonate diffuses outward while acid diffuses inward, equilibrating in the middle of the mucus layer. Additionally, the epithelial cells themselves express tight junctions via claudin and occludin proteins that prevent back-diffusion of hydrogen ions and maintain an intracellular pH of 7.2-7.4 despite exposure to luminal acid. The mucosa also expresses prostaglandin-mediated cytoprotection: locally produced prostaglandins (PGE2 and PGI2, via COX-1 and COX-2 enzymes) enhance mucus secretion, increase bicarbonate secretion, improve mucosal blood flow, and promote epithelial cell proliferation and restitution after minor injury.

The stomach produces approximately 1-2 liters of hydrochloric acid daily through the action of gastric parietal cells located in the fundic glands. The final secretion step involves the proton pump (H+/K+-ATPase), an apical membrane protein that actively transports H+ ions into the gastric lumen in exchange for K+ in an energy-dependent manner. This mechanism is regulated through two major pathways: the gastrin-gastrin receptor pathway (activated by antral G cells responding to peptides and amino acids) and the histamine-H2 receptor pathway (mediated by mast cells and enterochromaffin-like cells in the fundus). Acetylcholine (ACh) from vagal innervation acts on M3 muscarinic receptors on parietal cells to enhance acid secretion both directly and indirectly by stimulating gastrin and histamine release. The regulation of acid secretion is normally tightly controlled; basal acid output accounts for approximately 10% of maximal output, and physiologic stimuli (food intake) induce coordinated acid production without causing mucosal damage in healthy individuals. Conditions causing excessive acid (Zollinger-Ellison syndrome from gastrin-secreting tumors, or rarely retained antral mucosa after surgery) or impaired acid regulation can precipitate ulcer formation.

Helicobacter pylori, a microaerophilic gram-negative spiral bacterium, causes chronic active gastritis in approximately 50% of the world's population, yet progresses to PUD in only 10-15% of infected individuals. The pathogenesis involves both bacterial virulence factors and aberrant host immune responses. The bacteria express a urease enzyme that cleaves urea (abundant in gastric juice) to ammonia and CO2, creating a localized alkaline microenvironment that allows survival in the acidic stomach. The organism's spiral shape and flagellar motility enable penetration through the mucus layer to the epithelium. Once established, H. pylori expresses several virulence factors:

The host response to H. pylori involves intense activation of innate and adaptive immunity. Infected mucosa shows infiltration by CD4+ and CD8+ T lymphocytes, B cells producing IgG and IgA antibodies, and activation of macrophages and dendritic cells. This inflammatory response causes oxidative stress through increased production of reactive oxygen species (ROS), which damages epithelial cells, increases epithelial permeability, and further impairs the mucus-bicarbonate barrier. IL-1β, TNF-α, and IL-8 are upregulated, perpetuating the inflammatory cascade. In duodenal ulcers (the most common *H. pylori*-associated ulcer type), H. pylori primarily infects the stomach and antrum, causing hypersecretion of acid that overwhelms duodenal defenses. In gastric ulcers, the bacteria directly infect the ulcer margin, causing local mucosal damage and impaired healing.

NSAIDs cause ulceration through inhibition of cyclooxygenase (COX) enzymes, particularly the constitutively expressed COX-1 in gastric mucosa, leading to depletion of protective prostaglandins. NSAIDs are lipophilic weak acids that accumulate in gastric parietal cells and epithelial cells, causing direct topical injury and further reducing local prostaglandin production. The loss of PGE2 and PGI2 results in:

Unlike H. pylori ulcers, NSAID ulcers typically develop without significant preceding gastritis and are not preceded by increased acid secretion. In fact, some NSAID-induced gastric ulcers occur in achlorhydric patients. The mechanism is primarily mucosal protection failure rather than acid aggression. Additionally, NSAIDs inhibit platelet function through COX-1 inhibition, reducing clot formation and impairing hemostasis when bleeding occurs.

The interplay between aggressive acid secretion and mucosal defenses determines not only whether an ulcer develops but also its anatomic location. Duodenal ulcers typically occur in the first portion of the duodenum, where Brunner's glands (which secrete bicarbonate and mucus) are most abundant. These ulcers are associated with increased acid secretion in H. pylori infection—the bacteria in the antrum stimulate gastrin-producing G cells, leading to sustained hypersecretion of acid that overwhelms duodenal defenses. *H. pylori*-positive duodenal ulcers have elevated fasting serum gastrin levels and increased gastric acid output compared to controls. Gastric ulcers, particularly those on the lesser curve and gastric antrum, are associated with normal or even low acid secretion and result primarily from impaired mucosal defense. They occur at the junction between acid-secreting and mucus-secreting regions (the "gastric ulcer transition zone"), where local mucosal defense is compromised. NSAID-induced gastric ulcers are more common than duodenal ulcers; NSAIDs preferentially disrupt gastric mucosal defenses while duodenal defenses remain relatively preserved.

Once an ulcer forms, healing requires restoration of the epithelial barrier through several coordinated processes. Epithelial restitution (restoration of continuity without true regeneration) occurs within hours to days through spreading and migration of surviving epithelial cells from the ulcer margins, facilitated by prostaglandins and growth factors (hepatocyte growth factor, transforming growth factor-β). Over days to weeks, epithelial proliferation replaces lost cells through stem cell activation in the base of gastric glands. Angiogenesis occurs through vascular endothelial growth factor (VEGF) production by granulation tissue fibroblasts and myofibroblasts, restoring blood supply. Finally, matrix deposition by fibroblasts and collagen remodeling replace the damaged mucosa with new mucosa. Complete mucosal healing typically requires 4-12 weeks even with optimal therapy, as evidenced by endoscopic studies.

H. pylori is the single most common cause of peptic ulcer disease worldwide, accounting for 60-90% of duodenal ulcers and 60-70% of gastric ulcers in populations with high infection rates. Transmission occurs person-to-person through fecal-oral or oral-oral routes (particularly in developing countries with poor sanitation) or through contaminated food and water. Not all infected individuals develop ulcers; progression to PUD depends on bacterial virulence (CagA+, VacA s1m1 genotypes are more pathogenic), host genetic susceptibility (polymorphisms in IL-1β and TNF-α genes increase ulcer risk), and environmental factors (smoking, stress). In developed countries, the prevalence of H. pylori infection has declined to 5-15% due to improved sanitation and widespread eradication efforts, correspondingly reducing the proportion of PUD attributable to this organism.

NSAIDs are the second most common cause of PUD in developed nations, responsible for 15-25% of ulcers overall and 60-75% of ulcers in *H. pylori*-negative patients. Risk factors for NSAID-induced ulcers include: age >65 years (5-fold increase), prior ulcer history (3-4 fold increase), concurrent glucocorticoid use, concurrent anticoagulation therapy, high-dose NSAID therapy, and use of NSAIDs with longer half-lives (naproxen, piroxicam). The incidence of clinically significant ulcers (those causing symptoms or complications) is 2-4% per year in chronic NSAID users. Notably, low-dose aspirin (75-325 mg daily), increasingly prescribed for cardiovascular protection, increases peptic ulcer risk 2-5 fold and should be considered an equivalent risk to other NSAIDs. COX-2 selective inhibitors (coxibs such as celecoxib) reduce ulcer risk compared to non-selective NSAIDs by up to 50%, though they do not eliminate it entirely and carry increased cardiovascular risk.

Simultaneous H. pylori infection and NSAID use dramatically increases PUD risk compared to either factor alone—patients with both risk factors have 3-5 fold greater risk of ulcer complications than those with single risk factors. This synergistic effect reflects the convergence of impaired mucosal defense (from NSAIDs) and active mucosal inflammation (from H. pylori).

Gastrin-secreting neuroendocrine tumors, occurring as part of ZES or rarely in isolation, cause intractable peptic ulcers through extreme acid hypersecretion. Criteria for suspicion include: severe or refractory ulcers, multiple ulcers, ulcers in unusual locations (distal duodenum, jejunum), chronic diarrhea as a presenting symptom, or family history suggesting MEN-1 syndrome. Fasting serum gastrin >1000 pg/mL with gastric pH <2 is virtually diagnostic; the secretin stimulation test (paradoxical rise in gastrin >200 pg/mL above baseline after secretin administration) confirms the diagnosis.

Stress ulcers (more accurately termed acute stress-related mucosal injury) develop in critically ill patients with severe physiologic derangement, including major surgery, severe sepsis, extensive burns (Curling's ulcer), severe head trauma (Cushing's ulcer), or multi-organ failure. The pathogenesis involves mucosal ischemia (from hypotension, hypovolemia, or regional vasoconstriction in sepsis) combined with impaired mucosal defense and increased acid-peptic aggression. Historically responsible for 10-30% of fatal GI bleeding in critically ill patients, stress ulcers are now rare due to widespread PPI prophylaxis in ICU settings. These ulcers differ from chronic PUD in being multiple, superficial, and often silent until massive bleeding occurs.

Peptic ulcers occur in 5-10% of Crohn's disease patients, resulting from transmural inflammation extending into the stomach and duodenum. These ulcers are typically refractory to acid suppression alone and require optimization of Crohn's disease management.

Gastric adenocarcinoma occasionally presents with an "ulcer" on endoscopy; these are not true peptic ulcers but rather malignant lesions with central necrosis. Endoscopic biopsies of any gastric ulcer, particularly new-onset gastric (but not duodenal) ulcers in elderly patients or those with alarm features, are essential to exclude malignancy.

The hallmark symptom of peptic ulcer disease is epigastric pain, classically described as burning, gnawing, or aching in character and localized to the epigastrium (midline upper abdomen). The pain results from acid stimulation of exposed nerve endings in the ulcer base and surrounding inflamed mucosa. Important characteristics include:

Avoid: clarithromycin after prior macrolide use; tetracycline and bismuth in pregnancy and young children; alcohol with metronidazole (disulfiram-like reaction).