¹⁸F-FDG-PET/CT and ^99mTc-MIBI SPECT/CT myocardial perfusion imaging to evaluate for cardiac sarcoidosis: effect of age and sex

Objectives: To determine if there is a relationship between results of combined ¹⁸F-FDG-PET/CT (PET) & resting ^99mTc-MIBI SPECT/CT myocardial perfusion imaging (MPI), performed to evaluate for cardiac sarcoidosis, & demographic factors of age & sex.

Methods: Between 8/1/2016-12/20/2019, 69 pts (21 F; 48 M) with cardiac arrhythmias &/or non-ischemic cardiomyopathies, without significant coronary artery disease, underwent 93 combined PET & MPI studies to evaluate for cardiac sarcoidosis. Pts on immunosuppressive therapy & pts with indeterminate scan results were excluded from analysis. For pts undergoing multiple scans, only the first scan was included. A total of 51 pts (15 F; 36 M) were included in this IRB approved retrospective investigation. Pts followed a low carbohydrate, high fat diet the day before and fasted for a minimum of 18 hrs prior to imaging. MPI was performed first, 45 min following injection of 370 MBq ^99mTc-MIBI. PET imaging of the heart was performed 90 min following injection of 370-444 MBq ¹⁸F-FDG. A 2^nd PET, from base of skull to mid-thigh, was performed 12-15 min later, however, these results were not part of this investigation. One experienced reader interpreted cardiac PET scans as positive (focal or focal on diffuse myocardial uptake of FDG > left ventricular blood pool activity), negative (myocardial FDG activity ≤ left ventricular blood pool activity) or indeterminate (diffuse, uniform, segmental myocardial uptake of FDG, possibly related to incomplete suppression of physiologic myocardial glucose uptake or multiple granulomas) for cardiac sarcoidosis. MPI was interpreted as negative (normal myocardial perfusion) or positive (at least one perfusion defect). Results were classified as follows: Group 1: PET negative/ MPI negative; Group 2: PET positive/MPI negative; Group 3: PET positive/MPI positive; & Group 4: PET negative/MPI positive.

Results: Among the 51 pts, ages were normally distributed (Kolmogorov-Smirnov D = 0.07, p > 0.10), with mean age = 58±10 yrs, with similar ages for female & male pts (60±13 versus 57±9 yrs, p = 0.33). There were 18 positive & 33 negative PET studies, & 28 positive & 23 negative MPI studies. Logistic regression determined that positive PET studies were significantly associated with age (χ² = 9.2; p = 0.003), but not sex (χ² = 0.7; p = 0.40). ROC analysis determined that age ≤ 58 yrs discriminated positive from negative PET studies (ROC AUC accuracy = 75±8%, sensitivity = 78%, specificity = 67%, p = 0.001). Pts who had a positive PET were significantly younger than pts who had a negative PET (53±9 versus 61±9 yrs, p = 0.01). The proportion of positive PET studies was higher for younger than older pts (56% versus 15%, p = 0.002). In contrast, positive MPI studies were not associated with age (p = 0.93) or sex (p = 0.64). Pts who had a positive MPI were similar in age to pts who had a negative MPI (58±10 versus 58±11 yrs, p = 0.93). The proportion of MPI studies that were positive were similar for younger & older pts (56% versus 54%, p = 0.88). Among the 4 groups, Group 2 pts (positive PET, negative MPI) were the youngest pts.

Conclusions: A positive PET, when performed for the evaluation of cardiac sarcoidosis, indicates active inflammation, and a positive MPI, suggests scar. Our analysis demonstrated more positive PET studies in patients < 58 years of age, than in patients > 58 years, while MPI results were not associated with age, and neither PET nor MPI results were associated with sex. These findings suggest that in this series of pts with cardiac arrhythmias &/or non-ischemic cardiomyopathies, without significant coronary artery disease, cardiac inflammation was more common in younger patients, than older ones, while the incidence of scar was similar in both groups. When interpreting PET for the evaluation of cardiac sarcoidosis, it is advisable to take into consideration that positive readings may be more likely in younger pts than in older pts.