Introduction
Cardiac sarcoidosis is an inflammatory granulomatous disease of the heart that carries significant morbidity and mortality. Immunosuppressive therapy is the cornerstone of treatment, aiming to reduce myocardial inflammation and preserve cardiac function. This prospective observational study evaluates the usefulness of Ga-68 DOTANOC PET/CT, a somatostatin receptor imaging modality, for assessing treatment response in cardiac sarcoidosis using semi-quantitative metrics.
Why Ga-68 DOTANOC PET/CT?
Ga-68 DOTANOC binds to somatostatin receptor type 2A, which is abundantly expressed by inflammatory cells within granulomas and not by normal myocardium. Unlike F-18 FDG PET/CT, DOTANOC imaging does not demand stringent dietary preparation, a practical advantage in diverse patient populations. The study leverages two semi-quantitative measures—SUVmax (maximum standardized uptake value) in the left ventricular myocardium and the Disease Activity Score (DAS), calculated as the ratio of LV SUVmax to blood pool SUVmed—to track changes during therapy.
Methods
A total of 19 treatment-naïve patients with clinically diagnosed cardiac sarcoidosis were enrolled at Apollo Hospitals, Chennai, from July 2022 to September 2024. Each patient underwent baseline and post-treatment Ga-68 DOTANOC PET/CT, alongside myocardial perfusion imaging and echocardiography to assess cardiac function. Treatments followed standard immunosuppressive regimens (prednisolone, with occasional methotrexate or cyclophosphamide in select cases).
Imaging protocols included a targeted cardiac PET/CT with 111–185 MBq of Ga-68 DOTANOC, performed approximately 60 minutes after injection. Myocardial SUVmax was measured in the area of greatest uptake, while blood pool activity (SUVmed) was drawn in the descending thoracic aorta. Echocardiographic LVEF was measured by an experienced cardiologist blinded to PET/CT results.
Key Findings: Treatment Response Measured by Ga-68 DOTANOC PET/CT
After a mean treatment duration of 13.2 weeks, 18 of 19 patients demonstrated significant reductions in both SUVmax and DAS on post-treatment scans compared with baseline. Specifically, SUVmax fell from 2.67 ± 1.19 to 1.47 ± 0.40 (p = 0.001), and DAS declined from 3.35 ± 1.20 to 1.80 ± 0.52 (p = 0.001). Clinically, these patients were symptom-free, arrhythmia-free, and did not require hospitalization during the follow-up period. In 14 patients with baseline LV systolic dysfunction (LVEF < 50%), reductions in SUVmax and DAS correlated with a rise in LVEF, illustrating a negative relationship between LVEF and myocardial tracer uptake—SUVmax: −0.58 (p = 0.02) and DAS: −0.74 (p = 0.002).
One patient showed relative stability in quantitative metrics, yet remained symptom-free during the interval and eventually displayed a later reduction in uptake after switching to an alternative immunosuppressant therapy. Across the cohort, nodal involvement in Ga-68 DOTANOC uptake regressed in 11 of 12 patients who had nodal uptake at baseline, aligning with systemic treatment response.
Clinical and Imaging Correlations
The study found a concordance between reductions in Ga-68 DOTANOC uptake and improved myocardial perfusion, supporting the interpretation that decreased inflammatory burden accompanies enhanced perfusion and function. Importantly, the negative correlation with LVEF suggests DOTANOC PET/CT is a meaningful adjunct for therapy monitoring in cardiac sarcoidosis.
Authors caution that DOTANOC imaging reflects inflammatory activity primarily in the acute/early phase of disease. Fibrosis and scarring may not show receptor expression, so changes in uptake should be interpreted alongside perfusion and echocardiographic data. In a subset analysis, DAS proved to be a robust marker of disease activity and response, sometimes outperforming SUVmax in relation to LVEF improvements.
Implications for Practice
Ga-68 DOTANOC PET/CT offers several practical advantages for follow-up in cardiac sarcoidosis:
- Elimination of complex dietary preparation required by F-18 FDG PET/CT in many patients.
- Provision of quantitative and qualitative data to gauge inflammatory burden and therapy response.
- Potential to identify partial responders or non-responders early, guiding timely therapeutic adjustments.
While the findings are promising, the authors call for larger, multi-center trials to validate these results and to further delineate how best to integrate Ga-68 DOTANOC PET/CT with perfusion imaging and echocardiography in routine care.
Conclusion
In this prospective study, post-treatment Ga-68 DOTANOC PET/CT demonstrated a significant reduction in myocardial inflammatory burden in most patients with cardiac sarcoidosis and correlated with improved LVEF. The modality shows promise as a valuable tool for monitoring response to immunosuppressive therapy and may help tailor treatment strategies to individual patient trajectories.
Limitations and Future Directions
Limitations include the small sample size and potential variability in follow-up intervals. Future work should explore standardized imaging intervals, broader patient populations, and direct comparisons with F-18 FDG PET/CT and MRI to optimize response assessment in cardiac sarcoidosis.
