Does marijuana smoking affect the results of a cardiac Sarcoidosis (Sarcoid) Positron Emission Tomography (PET) scan?

Marijuana Smoking and Cardiac Sarcoidosis PET Scan Results

Marijuana smoking can affect the results of a cardiac sarcoidosis PET scan by potentially causing false positive findings due to altered myocardial glucose metabolism, necessitating temporary cessation of marijuana use before the scan.

Impact of Marijuana on Cardiac PET Imaging

Cardiac sarcoidosis PET scans rely on proper suppression of physiologic myocardial glucose uptake to accurately detect inflammatory activity. Marijuana can interfere with this process in several ways:

1. Altered glucose metabolism: Similar to how marijuana affects cardiovascular function, it may alter myocardial glucose metabolism, potentially leading to non-specific FDG uptake patterns.

2. Interference with myocardial suppression protocols: The EANM/SNMMI guidelines emphasize that optimal myocardial suppression is critical for accurate cardiac sarcoidosis diagnosis 1. Marijuana could compromise this suppression.

Recommended Protocol for Cardiac Sarcoidosis PET Imaging

Patient Preparation

• Myocardial suppression protocol is mandatory for cardiac sarcoidosis PET imaging 1
• Prolonged fasting (at least 12 hours) preceded by a high-fat, low/no carbohydrate diet for 24-48 hours 1
• Avoid marijuana smoking for at least 24-48 hours before the scan
• Some protocols include intravenous heparin (50 IU/kg) 15 minutes before tracer injection 1

Imaging Characteristics

• Cardiac sarcoidosis presents as focal or focal-on-diffuse uptake pattern 1
• Diffuse, isolated homogenous basal lateral wall, papillary muscle, or basal "ring" uptake typically represents physiological uptake due to poor suppression 1

Diagnostic Performance and Considerations

The diagnostic accuracy of FDG-PET/CT for cardiac sarcoidosis is significantly affected by patient preparation:

• Sensitivity: 84% (95% CI, 74-90%)
• Specificity: 82% (95% CI, 75-88%) 1

Meta-analyses show that diagnostic accuracy is significantly affected by:

• Fasting duration (p=0.01)
• Heparin administration before scanning (p=0.02) 2

Clinical Implications

1. Risk of false positives: Marijuana use prior to scanning may lead to inadequate myocardial suppression, resulting in diffuse uptake patterns that could be misinterpreted as inflammation.

2. Risk of false negatives: Alternatively, marijuana-induced metabolic changes could potentially mask true inflammatory activity in the myocardium.

3. Diagnostic algorithm:

   • For patients with known marijuana use, consider: a) Postponing the scan until 48-72 hours after last marijuana use b) Implementing a more rigorous myocardial suppression protocol c) Adding resting myocardial perfusion imaging to improve diagnostic accuracy 1

Additional Considerations

• Cardiac MRI is an alternative diagnostic tool for cardiac sarcoidosis with comparable specificity to PET 1
• For patients unable to abstain from marijuana, cardiac MRI might be preferred as it does not rely on glucose metabolism 1
• The American Thoracic Society recommends cardiac MRI as the first-line imaging modality for suspected cardiac sarcoidosis, with PET as an alternative when MRI is contraindicated 1

Conclusion

When evaluating a patient with suspected cardiac sarcoidosis who uses marijuana, clinicians should:

1. Advise temporary cessation of marijuana use before PET scanning
2. Ensure strict adherence to myocardial suppression protocols
3. Consider alternative imaging modalities like cardiac MRI if marijuana abstinence is not feasible
4. Interpret results cautiously, particularly if suboptimal myocardial suppression is observed