An internal medicine physician evaluates a 42-year-old male during an outpatient consultat… — USMLE Step 2 CK

An internal medicine physician evaluates a 42-year-old male during an outpatient consultation for refractory dyspepsia and frequent loose stools. Over the past eight months, the patient has experienced burning epigastric pain that is only transiently relieved by food intake. His medical history is notable for recurrent duodenal ulcers, for which he successfully completed a course of *Helicobacter pylori* eradication therapy a year ago. Following his physician's instructions, he discontinued all proton pump inhibitors fourteen days ago. He currently takes no medications. Vital signs are normal. Abdominal examination demonstrates localized epigastric tenderness to deep palpation without guarding.

Laboratory testing reveals the following:

Laboratory Test	Result	Reference Range
Serum calcium	$9.2$ mg/dL	$8.4 - 10.2$ mg/dL
Fasting serum gastrin	$480$ pg/mL	$< 110$ pg/mL
Gastric fluid pH	$1.8$	$1.5 - 3.5$

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

Secretin stimulation testAnswer
B
Somatostatin receptor scintigraphy
C
Empiric oral ciprofloxacin and metronidazole
D
Diagnostic laparoscopy
E
Measurement of serum vasoactive intestinal peptide

Answer

The correct answer is the secretin stimulation test.

The correct answer is the secretin stimulation test. This patient presents with classic features of Zollinger-Ellison syndrome (ZES), including multiple duodenal ulcers and chronic diarrhea (caused by the inactivation of pancreatic enzymes by massive gastric acid secretion). The diagnostic algorithm for ZES begins with stopping proton pump inhibitors and measuring a fasting serum gastrin level alongside gastric pH. If the gastric pH is

< 4.0

and the gastrin level is

> 1000

pg/mL, the diagnosis is confirmed. However, if the gastrin level is indeterminate (between

110

and

1000

pg/mL), a secretin stimulation test must be performed. Secretin paradoxically stimulates the release of gastrin from gastrinoma cells, leading to a marked rise in serum gastrin levels, which confirms the diagnosis.

Step-by-Step Solution

Analyze the clinical presentation.

The patient has refractory dyspepsia, recurrent duodenal ulcers despite prior H. pylori treatment, and chronic diarrhea, which strongly suggests a hypersecretory state like Zollinger-Ellison syndrome (ZES).

Recognizing the classic triad of recurrent peptic ulcer disease, chronic diarrhea, and resistance to standard therapy points toward a gastrinoma.

Interpret the initial diagnostic laboratory findings.

Gastric pH is low (

1.8

), confirming an acidic environment. Fasting serum gastrin is elevated (

480

pg/mL), but it is not completely diagnostic on its own.

A fasting serum gastrin level

> 1000

pg/mL in the presence of a gastric pH

< 4.0

is definitively diagnostic for ZES. A level between

110

and

1000

pg/mL is indeterminate and requires further testing.

Determine the appropriate confirmatory diagnostic test.

A secretin stimulation test is the next required step to confirm the diagnosis.

Normal gastric G cells are inhibited by secretin, but gastrinoma cells are paradoxically stimulated by it. An increase in serum gastrin of

> 120

pg/mL over the baseline after secretin administration confirms ZES.

Key Concept

Diagnosis of Zollinger-Ellison Syndrome

Estimated Time:1m 0s

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