Acute Pancreatitis: A High-Yield USMLE Review

Acute pancreatitis is acute inflammation of the pancreas accompanied by a systemic inflammatory response, ranging from mild, self-limited disease to life-threatening necrotizing pancreatitis. Gallstones and alcohol account for roughly 80% of cases. It is a high-yield exam topic for its classic presentation, the 2-of-3 diagnostic criteria, severity assessment, and complications such as infected necrosis.

Presentation

• Severe epigastric pain radiating to the back — a classic hallmark
• Relief when leaning forward and worsening when lying supine (the pancreas is retroperitoneal; leaning forward moves the inflamed gland away from the spine)
• Nausea and vomiting
• Signs of a systemic inflammatory response (SIRS) — fever, tachycardia
• History of heavy alcohol use or gallstone disease

Diagnosis

• Diagnosis requires 2 of 3: characteristic epigastric pain, lipase >3× the upper limit of normal, and characteristic imaging findings
• Lipase — expect markedly elevated levels
• LFTs — an ALT >3× ULN suggests gallstone etiology
• RUQ ultrasound — to evaluate for gallstones (obtain even in presumed alcoholic pancreatitis); note small stones and microlithiasis may be missed, in which case EUS or MRCP can detect them
• CBC and BMP to assess severity markers; calculate a severity score such as BISAP
• CT at 72–96 hours if the patient is not improving, to assess for necrosis and other local complications

Management

• Aggressive IV fluid resuscitation (lactated Ringer's preferred)
• Pain control (opioids)
• NPO initially, with resumption of oral diet as pain improves and appetite returns
• Treat the underlying cause — for gallstone pancreatitis, perform cholecystectomy before discharge; provide alcohol cessation counseling for alcoholic etiology
• Monitor for complications; for infected pancreatic necrosis use the step-up approach (antibiotics → drainage → necrosectomy)

High-yield

• Gallstones and alcohol cause ~80% of acute pancreatitis; ALT >3× ULN points to a gallstone etiology
• Fat necrosis with saponification is the pathognomonic tissue injury pattern (lipase release)
• Diagnose with 2 of 3: characteristic pain + lipase >3× ULN + imaging
• Gas bubbles within a peripancreatic necrotic collection are pathognomonic for infected necrosis — deterioration after initial improvement with fever and leukocytosis
• BISAP severity score: BUN >25, Impaired mental status, SIRS, Age >60, Pleural effusion; ≥3 = high mortality risk
• Severe pancreatitis (~20%) is defined by persistent organ failure >48 hours and carries 30–50% mortality

Pitfalls

• Do not stop at "idiopathic" — after negative ultrasound, alcohol history, triglycerides, and calcium, pursue occult microlithiasis (EUS/MRCP), drug-induced causes, genetic mutations (PRSS1, SPINK1, CFTR), autoimmune (IgG4) pancreatitis, and pancreatic divisum; 15–25% remain idiopathic and many are ultimately microlithiasis
• Failing to arrange cholecystectomy before discharge in gallstone pancreatitis
• Intervening too early on necrosis — infected necrosis is managed with a delayed step-up approach, not immediate open necrosectomy
• Skipping RUQ ultrasound in presumed alcoholic pancreatitis — always evaluate for gallstones