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Difficulty: Very hardDiagnostic Workup and Test Sequencing

A 45-year-old female is evaluated during a gastroenterology consultation for severe, refractory epigastric burning pain and voluminous, watery diarrhea that has persisted for the past eight months. She reports waking up multiple times at night due to the abdominal pain. She has been adherent to a twice-daily, high-dose proton pump inhibitor regimen for the past six months with minimal symptom relief.

An upper gastrointestinal endoscopy performed two days ago revealed prominent, hypertrophic gastric folds and multiple 1- to 2-cm deep ulcerations extending from the gastric antrum into the distal duodenum and proximal jejunum. She has no significant past medical history and takes no other medications.

Following specific instructions, the patient discontinued her proton pump inhibitor two weeks prior to laboratory evaluation, substituting it with a histamine-2 receptor antagonist that was strictly held for 48 hours before testing.

Laboratory results are as follows:

TestResultReference Range
Serum gastrin (fasting)520 pg/mL< 100 pg/mL
Gastric fluid pH1.41.5 - 3.5

Which of the following is the most appropriate next step in the diagnostic evaluation of this patient?

  1. Secretin stimulation testAnswer
  2. B
    Gallium-68 DOTATATE PET/CT scan
  3. C
    Multiphasic computed tomography of the abdomen and pelvis
  4. D
    Measurement of intact parathyroid hormone and serum ionized calcium
  5. E
    Measurement of serum vasoactive intestinal peptide

Answer

The correct answer is a secretin stimulation test.
The correct answer is a secretin stimulation test. This patient's presentation of refractory peptic ulcer disease in atypical locations (distal duodenum and jejunum), prominent gastric folds, and chronic diarrhea is highly suspicious for Zollinger-Ellison syndrome (ZES). The initial step in diagnosing ZES is demonstrating an inappropriately elevated fasting serum gastrin (FSG) level in the presence of gastric acid hypersecretion (gastric pH < 2.0). A pH < 2.0 excludes achlorhydria, which is the most common secondary cause of hypergastrinemia. While an FSG level > 1000 pg/mL in the presence of a gastric pH < 2.0 is definitively diagnostic for ZES, this patient's level falls in the equivocal range (between 110 and 1000 pg/mL). Therefore, biochemical confirmation requires a secretin stimulation test. In a healthy individual, secretin administration inhibits gastrin release; however, in a patient with a gastrinoma, secretin paradoxically stimulates a dramatic rise in serum gastrin (typically an increase of > 120 pg/mL over the basal level). Only after the diagnosis is biochemically confirmed should the clinician proceed to tumor localization imaging.

Step-by-Step Solution

1
Analyze the clinical presentation and endoscopic findings.
The patient has refractory peptic ulcer disease in atypical locations (distal duodenum/jejunum), prominent gastric folds, and chronic diarrhea.
These findings are classic for Zollinger-Ellison syndrome (ZES), a condition characterized by autonomous gastrin secretion from a neuroendocrine tumor (gastrinoma).
2
Interpret the laboratory data in the context of the clinical suspicion.
Fasting serum gastrin is elevated (520 pg/mL) in the presence of an appropriately acidic gastric pH (1.4).
A pH < 2.0 confirms that the hypergastrinemia is a primary overproduction (e.g., ZES) and excludes achlorhydria (e.g., pernicious anemia), which is the most common overall cause of elevated gastrin.
3
Determine the diagnostic threshold for ZES based on the gastrin level.
A gastrin level > 1000 pg/mL with a pH < 2.0 is definitively diagnostic for ZES. This patient's level of 520 pg/mL falls into the equivocal range (110 - 1000 pg/mL).
Equivocal gastrin levels require a provocative test to differentiate a gastrinoma from other causes of gastric acid hypersecretion.
4
Select the appropriate next test to confirm the diagnosis.
A secretin stimulation test must be performed.
Normal gastric G cells are inhibited by secretin, but gastrinoma cells paradoxically release gastrin in response to secretin. Biochemical confirmation must be established prior to any localization imaging.

Key Concept

Patients with suspected Zollinger-Ellison syndrome who have an equivocal fasting serum gastrin level (110–1000 pg/mL) and a gastric pH < 2.0 require a secretin stimulation test for biochemical confirmation prior to any localization imaging.
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Topics

Diagnostic Workup and Test Sequencing

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