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Difficulty: MediumDiagnostic Workup and Test Sequencing

A 45-year-old woman is evaluated in the gastroenterology clinic for a 9-month history of severe, burning epigastric pain and chronic watery diarrhea. Her symptoms have been refractory to high-dose omeprazole therapy. An esophagogastroduodenoscopy performed three weeks ago revealed thickened gastric folds and multiple ulcerations in the duodenal bulb and the distal duodenum. The patient was instructed to discontinue her proton pump inhibitor for one week prior to today's visit, utilizing only calcium carbonate antacids for symptom relief. Vital signs are within normal limits. Physical examination reveals mild epigastric tenderness. Laboratory testing shows a fasting serum gastrin level of 640 pg/mL (Normal: < 100 pg/mL). A concurrent gastric fluid analysis demonstrates a basal gastric pH of 1.5. Which of the following is the most appropriate next step in the diagnostic workup?

  1. Secretin stimulation testAnswer
  2. B
    Gallium-68 DOTATATE positron emission tomography
  3. C
    Computed tomography scan of the abdomen and pelvis
  4. D
    Fasting serum calcium and parathyroid hormone levels
  5. E
    Endoscopic ultrasonography

Answer

The most appropriate next step is a secretin stimulation test to biochemically confirm the diagnosis of Zollinger-Ellison syndrome.
This patient's presentation of refractory peptic ulcer disease, distal duodenal ulcers, and diarrhea is highly suspicious for Zollinger-Ellison syndrome (ZES). The initial workup for ZES involves measuring fasting serum gastrin (FSG) off proton pump inhibitor therapy and assessing gastric pH. A gastric pH < 2.0 confirms that hypergastrinemia is not secondary to achlorhydria. If the FSG is > 1,000 pg/mL, the diagnosis of ZES is definitively confirmed. However, if the FSG is elevated but < 1,000 pg/mL (as seen in this patient with 640 pg/mL), the value is considered equivocal. The correct next step is provocative testing with a secretin stimulation test. Secretin normally inhibits gastrin release from normal gastric G cells but paradoxically stimulates gastrin release from gastrinoma cells. An increase in serum gastrin of > 120 pg/mL above basal levels following secretin administration confirms ZES.

Step-by-Step Solution

1
Analyze the clinical presentation and endoscopic findings.
The patient has refractory peptic ulcer disease, distal duodenal ulcers, thickened gastric folds, and chronic diarrhea.
These findings are highly suspicious for Zollinger-Ellison syndrome (gastrinoma), prompting evaluation of gastrin and acid levels.
2
Interpret the laboratory findings.
The fasting serum gastrin is elevated (640 pg/mL) and gastric pH is acidic (1.5).
A gastric pH < 2.0 excludes achlorhydria as a cause of hypergastrinemia. However, the gastrin level is in the equivocal range (100 to 1,000 pg/mL).
3
Determine the appropriate sequencing to confirm the diagnosis.
A secretin stimulation test is indicated.
Because the gastrin level is not definitively diagnostic (> 1,000 pg/mL), provocative testing with secretin is required before proceeding to tumor localization imaging.

Key Concept

In the workup of Zollinger-Ellison syndrome, an equivocal fasting serum gastrin level (100 to 1,000 pg/mL) in the setting of gastric pH < 2.0 requires provocative biochemical testing with a secretin stimulation test before obtaining localization imaging.
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Diagnostic Workup and Test Sequencing

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