IJCS | Volume 33, Nº4, July and August 2020

395 Resting perfusion defects can be due to compression of the microvasculature by inflammation, with a mismatch between. 46 In the later phases of the disease, scarring/ fibrosis can be seen, in addition to a matching pattern with rest perfusion defect and no 18F-FDG uptake. However, not all patients with CS develop scarring. When multiple focal areas of FDG uptake, involving the basal antero-septum, basal inferior and basal lateral walls are present, CS should be considered. Some areas of scar with no inflammation (match) can coexist with areas of scar with inflammation (mismatch). The combination of both findings (mismatch) has been associated with the worst outcome, 51,52 as well as the presence of RV uptake. Challenges with FDG PET The diagnose of CS with 18F-FDG is often a challenge. Patients can have comorbidities such as ischemic cardiomyopathy that can make the diagnosis even more difficult. Scar can be seen in both diseases and the presence of hibernating myocardium can mimic areas of inflammation due to CS. The same can happen in patients with active myocarditis or systemic rheumatologic conditions with cardiac involvement. Studies of patients with ICD leads have to be interpreted carefully using both attenuation- corrected and non-attenuation-corrected images as false 18F-FDG uptake can be seen near the leads due to partial-volume artifact and misinterpreted as positive. One of the greatest challenges with 18F-FDG is the adequate preparation for the test, since a poor adherence to the diet may lead to diffuse 18F-FDG uptake, making the study uninterpretable. Moreover, up to 25% of the patients do not respond to any of the strategies to reduced myocardial uptake leading to a high rate of false-positives or inconclusive results. 32,53 Therefore, 18F-FDG PET studies for CS should be conducted in experienced centers, with qualified physicians, since false-positive studies could be harmful to immunosuppressed patients. Figures 3 and 4 illustrate two different cases before and after therapy. Prognosis Cardiac PET can help in the diagnosis and assessment of treatment response in CS. Given the risk of sudden cardiac death and the potential side effects of ICD, some studies have tried to identify how cardiac PET findings could be related to adverse cardiac events in a population with CS. Blankstein et al., 52 studied 118 patients who underwent PET with 18F-FDG and Rb-82 to assess inflammation and perfusion defect, and categorized them according to the imaging findings as (a) normal; (b) positive perfusion defect or glucose uptake; or (c) positive perfusion defect and glucose uptake. 52 They followed the patient for an average of 1.5 year to identify the outcomes of death and sustained ventricular tachycardia (VT). Among the patients, 47 (40%) had normal and 71 (60%) abnormal cardiac PET findings. During the follow-up, there were 31 (26%) adverse events, with 27 VT and 8 deaths. Cardiac PET was able to predict adverse event with the presence of both perfusion defect and abnormal FDG (findings present in 29% of the patients), with a hazard ratio of 3.9 (p<0.01). However, based on current knowledge, PET cannot rule in or out the need for ICD in CS patients. Table 3 – Positron emission tomography (PET) interpretation of the perfusion and metabolism findings PET findings Perfusion Normal Normal Abnormal (perfusion defect) Abnormal (perfusion defect) Metabolism Normal (negative) Diffuse / lateral wall uptake (non-specific) Focal increase Focal increase Multiple areas Normal (negative) Interpretation Normal Early disease Inflammation No scar Mismatch pattern Scar and inflammation Scar and no active inflammation Adapted from Blankstein et al. 58 Wiefels et al. 18F-FDG PET/CT and cardiac sarcoidosis Int J Cardiovasc Sci. 2020; 33(4):389-400 Review Article