An evaluation is requested for a 49-year-old male who reports a 6-month history of volumin… — USMLE Step 3

An evaluation is requested for a 49-year-old male who reports a 6-month history of voluminous, watery diarrhea and persistent epigastric pain. The patient notes that his symptoms have barely improved despite strict adherence to a high-dose oral omeprazole regimen. His medical history is notable for a duodenal ulcer that perforated and required surgical patch repair one year ago. His vital signs today are within normal limits. Following instructions to discontinue his proton pump inhibitor for seven days, the patient underwent an upper gastrointestinal endoscopy, which demonstrated unusually thickened gastric folds and the presence of two distinct ulcers in the postbulbar duodenum. Subsequent laboratory analysis reveals a fasting serum gastrin concentration of $580 \text{ pg/mL}$ (normal: $< 100 \text{ pg/mL}$ ) and a basal gastric pH of $1.4$ . Which of the following is the most appropriate next step in the diagnostic workup?

A
Gallium-68 DOTATATE positron emission tomography
B
Endoscopic ultrasound
Secretin stimulation testCevap
D
Measurement of serum calcium and intact parathyroid hormone levels
E
Measurement of serum anti-parietal cell antibodies

Cevap

The correct next step is the secretin stimulation test.

The patient's clinical presentation is highly suspicious for Zollinger-Ellison syndrome (ZES), caused by a gastrin-secreting neuroendocrine tumor (gastrinoma). The diagnostic workup for ZES begins with measuring fasting serum gastrin (FSG) and basal gastric pH. A gastric pH

< 2.0

indicates that the hypergastrinemia is primary. If the FSG is

> 1000 \text{ pg/mL}

with a pH

< 2.0

, the diagnosis of ZES is confirmed. However, if the FSG is elevated but

< 1000 \text{ pg/mL}

(as in this patient with

580 \text{ pg/mL}

), the results are considered equivocal. In such cases, a secretin stimulation test is required. 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 \text{ pg/mL}

above the basal level confirms the diagnosis of ZES.

Adım Adım Çözüm

Analyze the patient's clinical presentation and endoscopic findings.

The patient has refractory peptic ulcer disease, postbulbar ulcers, and chronic diarrhea, which are classic hallmark signs of Zollinger-Ellison syndrome (ZES).

Identifying the clinical syndrome guides the initial diagnostic hypothesis and determines the appropriateness of the preliminary tests.

Evaluate the preliminary laboratory results in the context of the medication history.

The fasting serum gastrin is elevated at

580 \text{ pg/mL}

, and the gastric pH is highly acidic at

1.4

, obtained after appropriately holding proton pump inhibitors.

A low gastric pH confirms that the hypergastrinemia is primary (gastrin-driven) rather than secondary to achlorhydria, ruling out conditions like atrophic gastritis.

Determine the appropriate diagnostic sequence based on the specific gastrin level.

Because the gastrin level falls in the equivocal range (between

110

and

1000 \text{ pg/mL}

), a secretin stimulation test is required to definitively confirm the diagnosis before proceeding to any anatomic imaging.

Following algorithmic guidelines prevents premature and unnecessary invasive testing or advanced imaging.

Anahtar Kavram

In the workup of suspected Zollinger-Ellison syndrome, a fasting serum gastrin level between

110

and

1000 \text{ pg/mL}

with an acidic gastric pH (

< 2.0

) is equivocal and requires a secretin stimulation test for definitive biochemical confirmation prior to anatomic tumor localization.

Tahmini Süre:1m 30s

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Cevap

Adım Adım Çözüm

Anahtar Kavram

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