Overview: Ga-68 DOTANOC as an inflammation tracer in cardiac sarcoidosis
Cardiac sarcoidosis (CS) is a granulomatous inflammatory disease affecting the heart, often with serious outcomes if not treated appropriately. Immunosuppressive therapy, typically steroids with possible addition of other agents, remains the mainstay of management. Traditional imaging has focused on identifying disease activity and guiding therapy. Recent evidence, including prospective data from a study conducted at Apollo Hospitals in Chennai, suggests that Ga-68 DOTANOC PET/CT can be a valuable tool for evaluating treatment response in CS by quantifying inflammatory burden.
Why Ga-68 DOTANOC? The science behind SSTR imaging
Ga-68 DOTANOC binds somatostatin receptor type 2A (SSTR2A), which is highly expressed by inflammatory cells in granulomas but not in normal myocardium. Unlike the more traditional F-18 FDG PET/CT, DOTANOC does not require stringent dietary preparation, making it appealing for patients who may struggle with diet adherence. The imaging modality provides semi-quantitative metrics, notably SUVmax and the Disease Activity Score (DAS), the latter calculated as the ratio of LV myocardial SUVmax to blood pool SUVmed. These metrics offer a way to track dynamic changes in myocardial inflammation in response to therapy.
What the study adds: response assessment in cardiac sarcoidosis using Ga-68 DOTANOC
The prospective observational study enrolled 19 treatment-naïve CS patients and followed them through 8–16 weeks of immunosuppressive therapy. All participants had pre- and post-treatment Ga-68 DOTANOC PET/CT scans, along with myocardial perfusion studies and echocardiography to assess functional changes. The key results showed:
- Significant regression in myocardial tracer uptake: SUVmax dropped from 2.67 ± 1.19 to 1.47 ± 0.40 (p = 0.001) after therapy in 18 of 19 patients.
- Concordant reduction in the Disease Activity Score (DAS): 3.35 ± 1.20 to 1.80 ± 0.52 (p = 0.001).
- Clinical improvement in all patients, with many achieving higher left ventricular ejection fraction (LVEF). In patients with baseline LV dysfunction (LVEF <50%), decreases in SUVmax and DAS correlated with increases in LVEF.
- Negative correlation between LVEF and PET/CT parameters: SUVmax and DAS declined as LVEF improved, indicating reduced inflammatory burden accompanies functional recovery.
Interestingly, nodal uptake in Ga-68 DOTANOC imaging resolved in most with treatment, supporting the systemic inflammatory nature of sarcoidosis. However, the authors caution that DOTANOC uptake only reflects acute/early inflammation; fibrosis may not demonstrate radiotracer activity, so imaging should be interpreted alongside perfusion and echocardiography to avoid underestimating disease chronicity.
Clinical implications: how this informs patient management
The ability to quantify response to immunosuppressive therapy using DOTANOC PET/CT has several practical implications:
- Objective monitoring: Serial measurements of SUVmax and DAS provide objective feedback on treatment effectiveness beyond symptom assessment alone.
- Early identification of non-responders: In one patient, partial response prompted switching to an alternative immunosuppressant, which was followed by subsequent improvement, illustrating the potential to tailor therapy timelines.
- Complementary to other imaging: Findings on DOTANOC PET/CT should be interpreted with concurrent myocardial perfusion studies and echocardiography to distinguish active inflammation from scar or fibrosis.
While promising, the study underscores that larger trials are needed to validate these findings and to better define thresholds for response. The small sample size and follow-up intervals are important considerations for generalizing results to broader CS populations.
Limitations and future directions
Limitations include the modest cohort size and variability in follow-up timing. Nevertheless, the study demonstrates a clear association between reductions in DOTANOC uptake and clinical as well as functional improvement. Future research should aim to standardize imaging protocols, establish robust response criteria, and compare DOTANOC PET/CT against F-18 FDG PET/CT and MRI in larger, diverse CS populations. Exploration of DOTANOC’s role in predicting long-term outcomes such as hospitalization rates and arrhythmia burden could further define its value in CS management.
Conclusion
Ga-68 DOTANOC PET/CT emerges as a promising modality for monitoring treatment response in cardiac sarcoidosis, offering quantitative measures of inflammatory activity that correlate with functional recovery. When used alongside perfusion imaging and echocardiography, it can enhance decision-making about immunosuppressive strategies and help identify partial responders who may benefit from therapy adjustment.
