Does Proton Pump Inhibitor (PPI) use affect the accuracy of a Dotanoc (Somatostatin Receptor) Positron Emission Tomography (PET) scan in patients with neuroendocrine tumors?

PPI Use Does Not Affect DOTANOC PET Scan Accuracy but Causes Physiologic Gastric Uptake

Proton pump inhibitors do not interfere with the diagnostic accuracy of DOTANOC PET scans for detecting neuroendocrine tumors, but they do cause diffuse, intense physiologic uptake in the stomach that should not be misinterpreted as pathologic. 1

Mechanism of PPI-Related Gastric Uptake

• PPIs induce enterochromaffin-like (ECL) cell hyperplasia in the gastric mucosa through hypergastrinemia, which increases somatostatin receptor expression and causes diffuse stomach uptake on DOTANOC imaging 1, 2
• This uptake pattern is benign and represents a physiologic response to chronic acid suppression, not tumor 1
• The gastric uptake can be intense and diffuse, potentially mimicking pathology, but is distinguished by its uniform distribution throughout the stomach wall 1

Critical Distinction: Chromogranin A vs. DOTANOC PET

It is essential to understand that PPIs affect chromogranin A levels (a biochemical marker) but do not impair DOTANOC PET scan performance (a functional imaging test). These are separate diagnostic modalities with different mechanisms:

• For chromogranin A testing: PPIs must be discontinued for at least 1 week before measurement, as they are the most common cause of false-positive elevation 3
• For DOTANOC PET scanning: PPIs do not need to be discontinued, as they do not reduce the scan's ability to detect neuroendocrine tumors 1

Diagnostic Performance of DOTANOC PET

• DOTANOC PET maintains excellent diagnostic accuracy with overall sensitivity of 94.8%, specificity of 86.5%, and accuracy of 91.4% for detecting neuroendocrine tumors 4
• For pancreatic NETs specifically, sensitivity is 85.7% with accuracy of 84.8% 5
• The scan reliably detects primary tumors (most commonly pancreatic) and metastases (most commonly hepatic) regardless of PPI use 4

Practical Interpretation Guidelines

When interpreting DOTANOC PET scans in patients on PPIs:

• Expect diffuse, uniform gastric wall uptake as a normal finding related to ECL cell hyperplasia 1
• Distinguish this benign pattern from focal gastric lesions (such as gastrinomas), which show localized rather than diffuse uptake 1
• Do not attribute diffuse gastric uptake to malignancy in PPI users 1
• The presence of gastric uptake does not indicate false-positive results elsewhere in the scan 4

Common Pitfalls to Avoid

• Do not delay DOTANOC PET scanning to discontinue PPIs - this is unnecessary and delays diagnosis 1
• Do not confuse the requirement to stop PPIs for chromogranin A testing with DOTANOC PET preparation - these are different tests with different requirements 3, 1
• Do not misinterpret diffuse gastric uptake as gastrinoma or other gastric NET - gastrinomas show focal uptake, while PPI-induced uptake is diffuse 1
• Be aware that sites of physiologic tracer concentration and inflammation can complicate interpretation, but this does not reduce overall diagnostic utility 6

Standard Preparation Protocol

According to current guidelines for somatostatin receptor PET imaging (which includes DOTANOC):

• Patients should be well-hydrated and empty their bladder before scanning 7
• No specific medication discontinuation is required for the scan itself 7
• Images are typically acquired 60 minutes post-injection 7
• The scan can proceed regardless of PPI use, with awareness of expected gastric uptake 1