Pancreatitis — Acute and Chronic

• Premature intracellular activation of pancreatic zymogens: In healthy pancreatic acinar cells, digestive enzymes are synthesized as inactive precursors (zymogens) and packaged in secretory granules destined for the duodenum. Normally, trypsinogen is activated to trypsin only in the small intestine via enterokinase (enteropeptidase). In pancreatitis, various triggers cause zymogens to be activated prematurely within acinar cells or in the pancreatic interstitium. Trypsin is the critical initiator enzyme—once formed, it catalyzes the activation of other zymogens in a cascade (chymotrypsinogen → chymotrypsin, proelastase → elastase, procarboxypeptidase → carboxypeptidase), amplifying tissue damage. Cellular stress signals, calcium dysregulation, and altered intracellular pH facilitate this aberrant activation. The protective mechanisms that normally prevent this (pancreatic secretory trypsin inhibitor [PSTI/SPINK1] and other endogenous protease inhibitors) are either overwhelmed or genetically deficient in predisposed individuals.

• Disruption of normal enzyme trafficking and acinar-ductal balance: The "two-compartment" hypothesis explains how normal enzyme secretion is maintained versus pathological activation. Under physiologic conditions, acinar cells maintain tight regulation through canalicular secretion directly into intralobular ducts. In AP, this compartmentalization breaks down—membrane blebs form, allowing mixing of digestive enzymes with lysosomal hydrolases (particularly cathepsin B), which can directly activate trypsinogen. Additionally, impaired ductal flow (from edema, strictures, or obstruction) causes increased intraductal pressure, leading to enzyme reflux into the interstitium. This is particularly important in biliary pancreatitis, where transient ampullary obstruction from gallstones causes increased pressure throughout the ductal system. Oxidative stress from mitochondrial dysfunction impairs the ATP-dependent sorting mechanisms that normally segregate hydrolytic enzymes, compounding the problem.

• Inflammatory cascade amplification with pancreatic and systemic consequences: Once local proteolysis begins, it triggers a robust inflammatory response that paradoxically amplifies injury beyond the initial triggering event. Damaged acinar cells and infiltrating immune cells (neutrophils, macrophages, T cells) release pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-8) and reactive oxygen species (ROS). These mediators increase pancreatic microvascular permeability, leading to edema, plasma extravasation, and hemoconcentration. The inflammatory mediators simultaneously activate the coagulation cascade (particularly tissue factor and thrombin) and the complement system (via both classical and alternative pathways), creating a feed-forward amplification loop. In severe AP, this local inflammation spills into the systemic circulation, producing the systemic inflammatory response syndrome (SIRS), which manifests clinically as fever, tachycardia, and potentially progressing to multiorgan dysfunction. The severity of the inflammatory response, not just the initial insult, determines progression to severe AP with complications. Pancreatic injury also triggers apoptosis and necrosis of acinar cells; necrosis is particularly damaging because it releases intracellular contents, whereas apoptosis (programmed cell death) can occur with minimal inflammation. The balance between these two forms of cell death influences disease severity.

• Vascular injury and ischemia as contributors to progression: The inflammatory mediators cause pancreatic microvascular injury through several mechanisms: direct endothelial damage from oxidative stress, platelet aggregation and thrombosis within pancreatic vessels, and increased capillary permeability. Pancreatic blood flow becomes compromised, particularly in areas of maximal inflammation, creating localized ischemia that compounds the enzymatic damage. This ischemia impairs the pancreatic tissue's ability to defend against oxidative stress and repair damage. In severe cases, progression to pancreatic necrosis occurs when the tissue injury overwhelms regenerative capacity. The extent of necrosis (pancreatic necrosis occurs in 20–30% of AP cases) strongly correlates with severity, mortality risk, and likelihood of organ failure. Infected necrosis (walled-off necrosis invaded by bacteria) represents a particular complication requiring intervention.

• Chronic pancreatitis pathophysiology—progressive parenchymal destruction and fibrosis: CP represents a fundamentally different process characterized by repeated episodes of inflammation (often triggered by the same mechanisms as AP) that cumulatively destroy parenchyma and trigger pathologic fibrosis. The stellate cell activation hypothesis posits that acinar injury triggers transformation of quiescent pancreatic stellate cells into activated myofibroblasts. These cells produce excessive extracellular matrix proteins (collagen types I and III), leading to progressive fibrosis that replaces lost acinar tissue. This fibrosis mechanically obstructs ducts, raises intraductal pressure, and perpetuates a cycle of inflammation. Concurrently, chronic oxidative stress, repeated calcium overload in acinar cells, and mitochondrial dysfunction impair cellular regeneration and promote further apoptosis. Unlike in AP where complete resolution can occur, in CP the fibrosis is largely irreversible. Over time, loss of functional acinar tissue leads to exocrine insufficiency (malabsorption from decreased enzyme secretion) and endocrine insufficiency (diabetes mellitus from beta cell loss). The inflammatory mediators released during each episode also contribute to pain through sensitization of pancreatic sensory nerves. In some CP patients with a genetic predisposition (CFTR, PRSS1, SPINK1 mutations), the threshold for activation is lowered, making them vulnerable to recurrent inflammation even from seemingly minor triggers.

Acute Pancreatitis

• Gallstone disease (biliary pancreatitis): Accounts for 40–50% of AP cases. Small stones (<5 mm) pass through the common bile duct and transiently lodge at the ampulla of Vater, causing sudden duct obstruction and pressure elevation. The obstruction may last only minutes to hours before the stone passes, yet this transient impediment is sufficient to trigger the inflammatory cascade. Women with cholecystitis are at higher risk than men. Microlithiasis (tiny stones or sludge not visible on ultrasound) can cause recurrent AP. The diagnosis is suggested by the presence of gallstones on imaging and elevated liver function tests, particularly elevated bilirubin and alkaline phosphatase at presentation.

• Alcohol consumption: Accounts for 25–35% of AP cases and is a dose-dependent risk factor. Acute alcohol intoxication triggers AP through several mechanisms: direct toxic effects on acinar cells, stimulation of pancreatic secretion, sphincter of Oddi spasm (increasing intraductal pressure), and lipid peroxidation. Notably, not all heavy drinkers develop AP, suggesting a genetic predisposition. Patients typically present after a recent binge or heavy drinking episode. Continued alcohol use is the primary determinant of progression from AP to CP.

• Hypertriglyceridemia (>1000–1500 mg/dL): Causes approximately 1–4% of AP cases but should always be considered, especially in young patients or those without gallstones or alcohol history. Elevated triglycerides increase pancreatic lipase demand and promote formation of toxic free fatty acids within the pancreatic vasculature. Conditions causing severe hypertriglyceridemia include familial chylomicronemia (type I or V lipoproteinemia), poorly controlled diabetes mellitus, estrogen therapy, and medications such as thiazide diuretics or corticosteroids. Serum triglyceride levels >1500 mg/dL carry substantial AP risk; levels <1000 mg/dL are less commonly causative alone.

• Medications: Numerous drugs are implicated in AP; important ones include azathioprine, 6-mercaptopurine, sulfonamides, valproic acid, didanosine, pentamidine, estrogens, corticosteroids, l-asparaginase, mesalamine, and thiazide diuretics. The exact mechanisms vary but include direct toxic effects, immunologic reactions, and metabolic disruption. Medication-induced AP typically occurs within weeks of drug initiation and should be suspected when other causes are excluded. Rechallenge with the offending agent typically reproduces AP, confirming causality.

• Endoscopic retrograde cholangiopancreatography (ERCP): Procedure-related pancreatitis occurs in 3–7% of ERCP cases, with higher rates in patients with sphincter of Oddi dysfunction, difficult cannulation, or pancreatic sphincterotomy. Post-ERCP AP is usually mild but can be severe. Risk factors include younger age, female sex, and normal serum bilirubin.

• Trauma: Blunt abdominal trauma (motor vehicle accident, falls) or penetrating trauma can directly injure the pancreas, causing AP. Pancreatic duct disruption is particularly likely to cause AP. Trauma-related pancreatitis often manifests with significant elevations in pancreatic enzymes.

• Genetic predisposition: Mutations in genes encoding cationic trypsinogen (PRSS1), pancreatic secretory trypsin inhibitor (SPINK1/PSTI), and the cystic fibrosis transmembrane conductance regulator (CFTR) predispose to both recurrent AP and CP. Hereditary pancreatitis (PRSS1 mutations) presents as recurrent AP in childhood or adolescence. SPINK1 and CFTR mutations increase risk of idiopathic pancreatitis.

• Metabolic and anatomic factors:
• Hypercalcemia (primary hyperparathyroidism, sarcoidosis, malignancy, vitamin D intoxication) causes AP through unclear mechanisms; calcium elevation itself doesn't necessarily correlate with AP risk.
• Anatomic abnormalities including pancreatic divisum (failure of fusion of dorsal and ventral pancreatic ducts), sphincter of Oddi dysfunction, and pancreatic ductal anomalies increase susceptibility to obstruction-related AP.
• Autoimmune pancreatitis (discussed separately but can present with acute inflammation) is associated with elevated IgG4 levels and autoantibodies.

• Infections: Viral infections (mumps, Coxsackie B, HIV, cytomegalovirus) and bacterial infections (rarely) can trigger AP, though the incidence has declined with improved vaccination coverage.

• Idiopathic pancreatitis: Accounts for 10–15% of AP cases after thorough investigation. Recurrent idiopathic AP suggests genetic susceptibility or undetected microlithiasis.

Chronic Pancreatitis

• Alcohol abuse: The leading cause of CP in developed countries, accounting for 70–80% of cases. Unlike the acute setting, chronic AP usually requires chronic heavy alcohol consumption (typically >40–50 g/day for men, >20 g/day for women over 10+ years). The mechanism involves repeated cycles of inflammation, oxidative stress, and fibrosis triggered by alcohol metabolites.

• Smoking: An independent risk factor for CP that may synergize with alcohol. Cigarette smoking increases the risk of CP progression and pancreatic cancer in patients with CP.

• Genetic mutations: CFTR mutations (cystic fibrosis phenotype and CFTR-related disorders), PRSS1 mutations (hereditary pancreatitis with autosomal dominant inheritance and 50% lifetime risk of CP), and SPINK1 mutations predispose to CP. These mutations impair normal protective mechanisms and promote susceptibility to inflammatory triggers.

• Autoimmune pancreatitis: Type 1 (associated with elevated IgG4) and Type 2 (more common in younger patients, associated with ANA) represent distinct immune-mediated pathways to CP. Type 1 often responds to corticosteroid therapy.

• Obstruction: Chronic ductal obstruction from strictures, stones, or neoplasm can lead to CP through mechanisms of increased intraductal pressure and recurrent inflammation.

• Tropical pancreatitis: Endemic in parts of Africa, India, and Southeast Asia; associated with cassava consumption and high tannin intake; presents as early-onset CP in young, non-alcoholic patients.

Acute Pancreatitis

• Epigastric abdominal pain (cardinal symptom): Typically the presenting complaint; pain is sudden in onset and severe (8–10/10 intensity), constant rather than colicky, and located in the epigastrium with radiation to the back. The pain results from pancreatic inflammation and stretching of the pancreatic capsule, both of which activate visceral nociceptors. Patients often adopt a flexed posture (knees drawn toward chest) to relieve pain, which partially relaxes the abdominal wall. The pain typically peaks over 30 minutes to a few hours and persists for hours to days. In biliary pancreatitis, the pain may follow a fatty meal; in alcohol-induced pancreatitis, it often occurs the day after alcohol consumption.

• Nausea and vomiting: Occur in 70–90% of patients; result from visceral peritoneal irritation and the inflammatory response. Vomiting may be severe and refractory to antiemetics, contributing to dehydration. The presence of vomiting suggests more severe inflammation.

• Constitutional symptoms: Fever (temperature typically 38–39°C) reflects the inflammatory response; absence of fever should prompt consideration of alternative diagnoses. Malaise and weakness occur from systemic inflammation and dehydration.

• Physical examination findings:
• Epigastric tenderness: Direct palpation over the pancreas (located deep in the epigastrium) typically elicits tenderness; peritoneal signs (rebound, guarding) indicate pancreatic necrosis or progressing inflammation.
• Cullen sign and Grey Turner sign: These are classic findings indicating hemorrhagic pancreatitis with retroperitoneal bleeding. Cullen sign is bruising around the umbilicus (rare); Grey Turner sign is flank ecchymosis. Both indicate severe disease with high mortality if present.
• Tachycardia, hypotension, and signs of shock: In severe AP, particularly in cases with significant necrosis or infected necrosis, patients may present with tachycardia, hypotension, and signs of systemic shock. This reflects the massive inflammatory cascade and fluid sequestration into the pancreatic interstitium and retroperitoneum (third-spacing), which can lead to hypovolemic shock if fluid resuscitation is inadequate.

Chronic Pancreatitis

• Chronic epigastric pain (distinct from acute): Pain in CP is typically chronic, mild to moderate (4–7/10), and may be continuous or episodic. Pain location is midepigastric and radiates to the back. Unlike AP, the pain develops insidiously over weeks to months and may fluctuate. Some patients experience pain-free periods, and a subset (particularly long-standing cases) have "burned-out" CP with minimal pain. Pain results from chronic inflammation, increased ductal pressure, and sensitization of pancreatic sensory nerves.

• Exocrine insufficiency symptoms: Loss of functional acinar tissue leads to decreased pancreatic enzyme secretion and malabsorption. Patients report steatorrhea (oily, floating, foul-smelling stools due to unabsorbed fat); typically appears when >90% of pancreatic exocrine function is lost. Associated symptoms include diarrhea, bloating, weight loss despite adequate caloric intake, and deficiencies in fat-soluble vitamins (A, D, E, K). The malabsorption can be profound, with patients losing 5–10 kg of body weight.

• Endocrine insufficiency (diabetes mellitus): Develops in 30–50% of CP patients as beta cells are progressively destroyed by chronic inflammation and fibrosis. Diabetes in CP ("pancreatogenic diabetes") is often brittle, with

Establishing the diagnosis — Revised Atlanta criteria (2 of 3 required)

• Characteristic pain: acute epigastric pain radiating to the back, as described above.
• Serum lipase (or amylase) ≥3× the upper limit of normal: lipase is the test of choice — it rises within hours, stays elevated 8–14 days, and is more specific than amylase (amylase also comes from salivary glands, fallopian tube, and is raised in macroamylasemia). Critically, the magnitude of enzyme elevation does not correlate with severity, and serial enzymes have no prognostic value. In severe hypertriglyceridemia, assay interference can produce a falsely normal amylase — dilute the specimen.
• Characteristic imaging: contrast-enhanced CT or MRI showing an edematous, poorly enhancing pancreas with peripancreatic fat stranding. If pain and lipase already establish the diagnosis, cross-sectional imaging is not required at presentation.

Sequencing the workup (ACG acute pancreatitis guideline)

• Transabdominal ultrasound in every patient on admission to look for gallstones and biliary dilation — the single most common etiology.
• ALT >3× ULN has high positive predictive value for a biliary cause; also send triglycerides and calcium.
• CECT is best deferred to 72–96 hours — necrosis is not radiographically apparent earlier, so early CT underestimates disease. Obtain it sooner only if the diagnosis is uncertain or the patient deteriorates.
• MRCP or EUS for suspected retained choledocholithiasis or recurrent "idiopathic" attacks (microlithiasis, divisum).

Severity scoring

• Ranson criteria: on admission — age >55, WBC >16,000, glucose >200 mg/dL, AST >250, LDH >350; at 48 hours — hematocrit fall >10%, BUN rise >5 mg/dL, calcium <8 mg/dL, PaO₂ <60 mmHg, base deficit >4, fluid sequestration >6 L. Classic on exams but clinically limited because it takes 48 hours.
• BISAP (BUN >25, Impaired mentation, SIRS, Age >60, Pleural effusion) and rising BUN/hematocrit are faster bedside predictors. Revised Atlanta grades severity by organ failure: transient (<48 h) = moderately severe; persistent = severe.

Immediate stabilization (first 24–48 hours)

• Isotonic crystalloid, preferably lactated Ringer's: the ACG favors LR over normal saline (large-volume saline causes hyperchloremic acidosis, and LR is associated with less inflammatory response). Resuscitation should be goal-directed and moderate — titrate to heart rate, mean arterial pressure, urine output, and falling BUN/hematocrit. Randomized data (the WATERFALL trial) showed that aggressive fixed-rate resuscitation increases fluid overload without benefit, so "more is better" is no longer correct.
• Analgesia with opioids (e.g., hydromorphone or fentanyl). The old teaching that morphine is contraindicated because of sphincter of Oddi spasm is not supported by evidence — do not withhold opioids.
• Early enteral nutrition: begin a low-fat oral diet within 24 hours as tolerated rather than keeping the patient NPO; use nasogastric or nasojejunal feeding if intolerant. Enteral feeding maintains gut mucosal integrity and reduces bacterial translocation. Parenteral nutrition is discouraged (AGA, ACG).

What not to do

• No prophylactic antibiotics, even in sterile necrosis (ACG/AGA) — they do not reduce mortality and select for fungal and resistant infection. Antibiotics with pancreatic penetration (a carbapenem such as meropenem) are reserved for suspected infected necrosis or extrapancreatic infection.
• No routine ERCP in biliary pancreatitis. Urgent ERCP (within 24 hours) is indicated only for concurrent cholangitis or persistent biliary obstruction.

Etiology-directed and definitive therapy

• Gallstone pancreatitis: same-admission laparoscopic cholecystectomy for mild disease before discharge (ACG) — delay markedly increases recurrence. Defer surgery in necrotizing disease until collections resolve or stabilize.
• Hypertriglyceridemic pancreatitis: IV insulin infusion (activates lipoprotein lipase) ± apheresis acutely; fibrate (fenofibrate) long term.
• Necrotizing pancreatitis: delay intervention ≥4 weeks to allow walled-off necrosis, then use a step-up approach — endoscopic transmural or percutaneous drainage first, minimally invasive necrosectomy only if needed. Open necrosectomy is a last resort.
• Autoimmune (IgG4) pancreatitis: corticosteroids.

Chronic pancreatitis

• Pancreatic enzyme replacement therapy (lipase-containing pancrelipase) with meals, plus acid suppression, for steatorrhea; supplement fat-soluble vitamins.
• Absolute alcohol and tobacco cessation; non-opioid analgesia with adjuncts (pregabalin) before escalating opioids; celiac plexus block, endoscopic duct decompression, or lateral pancreaticojejunostomy (Puestow) for a dilated duct.

Local complications

• Acute peripancreatic fluid collection → pseudocyst: a collection persisting beyond 4 weeks develops a fibrous/granulation-tissue wall with no epithelial lining (hence "pseudo"). Signals: persistent pain, early satiety, palpable mass, or a re-rising lipase. Most resolve; drain (endoscopic cystgastrostomy preferred) only if symptomatic, infected, or obstructing.
• Acute necrotic collection → walled-off necrosis: non-enhancing pancreatic parenchyma on CECT.
• Infected necrosis — EMERGENCY: gut translocation seeds necrotic tissue, typically at 7–10 days. Signals are clinical deterioration, new fever/leukocytosis, and retroperitoneal gas on CT. Start a carbapenem and pursue step-up drainage; it is the leading cause of late mortality.
• Splenic vein thrombosis: perivenous inflammation → thrombosis → isolated gastric varices with a normal liver. Presents as upper GI bleeding; splenectomy is curative.
• Pseudoaneurysm (splenic or gastroduodenal artery) — EMERGENCY: enzymatic erosion of the arterial wall causes sudden hemorrhage into a pseudocyst or GI tract; treat with angiographic embolization.
• Pancreatic duct disruption: pancreatic ascites or a persistent left pleural effusion with very high fluid amylase.

Systemic complications

• ARDS — EMERGENCY: circulating phospholipase A2 degrades surfactant and cytokines increase capillary permeability; hypoxemia with bilateral infiltrates in the first days.
• Hypocalcemia: released lipase generates free fatty acids that chelate calcium (saponification in fat necrosis); look for Chvostek and Trousseau signs — a Ranson criterion and a poor prognostic marker.
• Hypovolemic shock and AKI from retroperitoneal third-spacing; abdominal compartment syndrome if intra-abdominal pressure rises.
• **DIC, ileus, and rarely *Purtscher retinopathy*** (sudden vision loss from complement-mediated retinal microvascular occlusion).

Complications of chronic disease and of therapy

• Pancreatogenic (type 3c) diabetes: loss of both beta and alpha cells makes it brittle with a high hypoglycemia risk on insulin.
• Fat-soluble vitamin deficiency and metabolic bone disease; pancreatic ductal adenocarcinoma risk rises with disease duration — new painless jaundice or accelerated weight loss demands imaging.
• Iatrogenic: fluid overload/pulmonary edema from over-resuscitation, catheter sepsis with parenteral nutrition, post-ERCP pancreatitis, and opioid dependence from chronic pain management.

• Lipase ≥3× ULN is the diagnostic enzyme: more sensitive and specific than amylase and elevated longer. The height of the value predicts nothing about severity — a stem describing a lipase of 3,000 does not mean severe disease.
• Gallstones and alcohol account for the large majority of cases: with abdominal pain plus lipase elevation, the single best next step is transabdominal ultrasound, not CT. An ALT elevated >3× ULN points strongly to a biliary cause.
• Do not order early CT: necrosis is invisible before roughly 72 hours. Reserve contrast-enhanced CT for diagnostic uncertainty or clinical deterioration.
• Prophylactic antibiotics are wrong in sterile necrotizing pancreatitis (ACG/AGA) — the most frequently tested management distractor. Treat only proven or strongly suspected infected necrosis, suggested by gas within the collection on CT plus deterioration.
• Same-admission cholecystectomy after mild gallstone pancreatitis is the guideline answer; discharging the patient for interval surgery is the trap. Urgent ERCP is only for concomitant cholangitis or persistent obstruction.
• A fluid collection becomes a pseudocyst at 4 weeks and is lined by granulation tissue, not epithelium. Asymptomatic pseudocysts are observed, not drained.
• Isolated gastric varices with a normal liver = splenic vein thrombosis from pancreatitis; hypocalcemia with tetany = fat saponification; hypoxemia at 48 hours = ARDS from phospholipase A2.
• In chronic pancreatitis, lipase and amylase are typically normal — this is the classic distractor. Diagnose with pancreatic calcifications on CT and a low fecal elastase-1, and treat steatorrhea with pancreatic enzyme replacement. Morphine is not contraindicated in acute pancreatitis, and long-standing chronic pancreatitis raises the risk of pancreatic adenocarcinoma.