USMLE® Step 1 Question of the Day: Acute Pancreatitis

USMLE® Step 1 Question of the Day: Acute Pancreatitis

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Each week, Osmosis shares a USMLE® Step 1-style practice question to test your knowledge of medical topics. Today’s case involves a 44-year-old man with abdominal pain and nausea. Abdominal examination shows tenderness and rigidity over the epigastric and periumbilical regions. Can you figure it out?

A 44-year-old man comes to the emergency department with abdominal pain and nausea for the past 24 hours. The pain started a few hours after dinner, and he describes it as constant pain in the upper part of his abdomen that radiates to his back and flanks. The patient also reports nausea, intermittent vomiting, and abdominal distention. Family history is significant for recurrent episodes of pancreatitis in his father and paternal uncle. He reports drinking an average of 2 alcoholic drinks per week. His temperature is 37.7ºC (99.9ºF), pulse is 92/min, respirations are 20/min, peripheral oxygen saturation is 96%, and blood pressure is 149/94 mmHg. He appears distressed and anxious. Abdominal examination shows tenderness and rigidity over the epigastric and periumbilical regions. Bowel sounds are diminished. No bruising of the umbilicus or flanks are seen. Which of the following laboratory results is the most specific in diagnosing this patient’s condition?

A. Serum amylase > 3 times the upper limit of normal

B. Serum lipase > 3 times the upper limit of normal

C. Serum bilirubin > 4.0 mg/dL

D. Elevated blood alcohol level

E. Blood urea nitrogen (BUN) level > 22 mg/dLScroll down to find the answer!

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The correct answer to today’s USMLE® Step 1 Question is…

B. Serum lipase > 3 times the upper limit of normal

Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!

Incorrect answer explanations

The incorrect answers to today’s USMLE® Step 1 Question are…

A. Serum amylase > 3 times the upper limit of normal

Incorrect: Although serum amylase elevation may be used to show biochemical evidence of acute pancreatitis, it is affected by serum pH, lipids, and bowel inflammation, and is prone to false elevations or spuriously normal results. Therefore it is not the most specific in diagnosing this patient’s acute pancreatitis.

C. Serum bilirubin > 4.0 mg/dL

Incorrect: Although hyperbilirubinemia may occur in up to 10% of patients with acute pancreatitis, bilirubin elevations are not specific to pancreatitis and do not contribute to the diagnosis. Serum bilirubin levels return to normal in 4-7 days.

D. Elevated blood alcohol level

Incorrect: Although alcohol abuse may cause acute pancreatitis in a dose-dependent manner, this patient only consumes 2 beers/week, which is unlikely to cause acute pancreatitis. Instead, his underlying familial hypertriglyceridemia is likely the cause of pancreatitis.

E. Blood urea nitrogen (BUN) level > 22 mg/dL

Incorrect: Azotemia (BUN >22 mg/dL) suggests more severe pancreatitis that is causing vascular permeability and intravascular volume depletion or hemorrhage. However, azotemia is not specific for acute pancreatitis and is not included in the diagnostic criteria.

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Main Explanation

This patient is presenting with constant abdominal pain localized in the epigastric region that radiates to the back, highly suggestive of acute pancreatitis. Acute pancreatitis occurs when pancreatic enzymes are inappropriately activated, leading to tissue damage and an inflammatory response. This patient has a family history of recurrent pancreatitis in his father and paternal uncle, suggesting the diagnosis of familial hypertriglyceridemia, an autosomal dominant condition. The high concentration of serum triglycerides can cause acute pancreatitis because when pancreatic cells encounter triglycerides, they release lipase to break the triglycerides down into free fatty acids; excess free fatty acids can subsequently injure the pancreas.

The most common causes of pancreatitis are gallstones and alcohol toxicity. The other causes of pancreatitis can be easily remembered by the mnemonic “I GET SMASHED”

The most common causes of pancreatitis are gallstones and alcohol toxicity. The other causes of pancreatitis can be easily remembered by the mnemonic

To make a diagnosis of acute pancreatitis (from any cause), one needs 2 out of 3 of the following criteria:

  • clinical symptoms, such as persistent, severe, epigastric pain with tenderness on palpation
  • laboratory studies demonstrating serum amylase or lipase greater than 3 times the upper limit of normal; lipase remains elevated for a longer period of time and has a higher specificity as compared with amylase
  • imaging (computed tomography, magnetic resonance (MR), ultrasonography) showing focal or diffuse enlargement of the pancreas

In this patient with a characteristic clinical presentation, the demonstration of an elevated serum amylase or lipase level will confirm the diagnosis of acute pancreatitis. However, serum amylase may be spuriously normal in patients with hypertriglyceridemia and spuriously elevated in patients with acidemia (arterial pH ≤ 7.32), therefore serum lipase is the preferred laboratory test for diagnosing acute pancreatitis. It is important to note, however, that there is no correlation between the severity of pancreatitis and the degree of serum lipase and amylase elevations. Additionally, an elevation in serum triglyceride levels is not sufficient to diagnose acute pancreatitis. Hyperbilirubinemia, leukocytosis, azotemia, and hypoglycemia are suggestive of more severe disease, but are not themselves diagnostic of acute pancreatitis.

What is acute pancreatitis? Acute pancreatitis describes a sudden inflammation of the pancreas, which can lead to a variety of severe complications.

Major Takeaway

Acute pancreatitis is characterized by epigastric abdominal pain radiating to the back, often with nausea and vomiting. The diagnosis is made by meeting 2 of the 3 clinical, laboratory, and imaging criteria. The preferred diagnostic laboratory test for acute pancreatitis is a serum lipase greater than 3 times the upper limit of normal.

References

Conwell, D. L., Banks, P. A., & Greenberger, N. J. (2018). Acute and Chronic Pancreatitis. In J. L. Jameson, A. S. Fauci, D. L. Kasper, S. L. Hauser, D. L. Longo, & J. Loscalzo (Eds.), Harrison’s Principles of Internal Medicine (20th ed.). Retrieved from accessmedicine.mhmedical.com/content.aspx?aid=1160016107

Toouli J, Brooke-Smith M, Bassi C, et al. Guidelines for the management of acute pancreatitis. J Gastroenterol Hepatol. 2002;17 Suppl:S15‐S39. doi:10.1046/j.1440-1746.17.s1.2.x

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