In suspected cardiac sarcoidosis, which pattern suggests scar tissue rather than active disease?

• A. absence of FDG uptake with perfusion defects or late gadolinium enhancement
• B. diffuse FDG uptake with no perfusion defects
• C. no imaging abnormalities
• D. increased perfusion with FDG uptake

Answer: (A)

Distinguishing scar from active inflammation in cardiac sarcoidosis relies on combining metabolic and perfusion/imaging findings. Scar tissue is nonmetabolic, so areas of scar will not take up the FDG tracer. At the same time, these areas show structural damage on perfusion imaging or MRI with late gadolinium enhancement. Put together, the pattern of no FDG uptake in the heart alongside perfusion defects or LGE signals past damage rather than ongoing inflammation.

In contrast, active inflammation would typically show metabolic activity with FDG uptake, reflecting inflammatory cells at work, though the exact perfusion pattern can vary. Diffuse FDG uptake can be non-specific and sometimes results from inadequate suppression of physiologic myocardial glucose uptake, while no imaging abnormalities or patterns of increased perfusion with FDG uptake are more indicative of active disease rather than scar.