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Whole-Body [\(^{18}\)F]FDG PET/CT Can Alter Diagnosis in Patients with Suspected Rheumatic Disease
(2021)
The 2-deoxy-d-[\(^{18}\)F]fluoro-D-glucose (FDG) positron emission tomography/computed tomography (PET/CT) is widely utilized to assess the vascular and articular inflammatory burden of patients with a suspected diagnosis of rheumatic disease. We aimed to elucidate the impact of [\(^{18}\)F]FDG PET/CT on change in initially suspected diagnosis in patients at the time of the scan. Thirty-four patients, who had undergone [\(^{18}\)F]FDG PET/CT, were enrolled and the initially suspected diagnosis prior to [18F]FDG PET/CT was compared to the final diagnosis. In addition, a semi-quantitative analysis including vessel wall-to-liver (VLR) and joint-to-liver (JLR) ratios was also conducted. Prior to [\(^{18}\)F]FDG PET/CT, 22/34 (64.7%) of patients did not have an established diagnosis, whereas in 7/34 (20.6%), polymyalgia rheumatica (PMR) was suspected, and in 5/34 (14.7%), giant cell arteritis (GCA) was suspected by the referring rheumatologists. After [\(^{18}\)F]FDG PET/CT, the diagnosis was GCA in 19/34 (55.9%), combined GCA and PMR (GCA + PMR) in 9/34 (26.5%) and PMR in the remaining 6/34 (17.6%). As such, [\(^{18}\)F]FDG PET/CT altered suspected diagnosis in 28/34 (82.4%), including in all unclear cases. VLR of patients whose final diagnosis was GCA tended to be significantly higher when compared to VLR in PMR (GCA, 1.01 ± 0.08 (95%CI, 0.95–1.1) vs. PMR, 0.92 ± 0.1 (95%CI, 0.85–0.99), p = 0.07), but not when compared to PMR + GCA (1.04 ± 0.14 (95%CI, 0.95–1.13), p = 1). JLR of individuals finally diagnosed with PMR (0.94 ± 0.16, (95%CI, 0.83–1.06)), however, was significantly increased relative to JLR in GCA (0.58 ± 0.04 (95%CI, 0.55–0.61)) and GCA + PMR (0.64 ± 0.09 (95%CI, 0.57–0.71); p < 0.0001, respectively). In individuals with a suspected diagnosis of rheumatic disease, an inflammatory-directed [\(^{18}\)F]FDG PET/CT can alter diagnosis in the majority of the cases, particularly in subjects who were referred because of diagnostic uncertainty. Semi-quantitative assessment may be helpful in establishing a final diagnosis of PMR, supporting the notion that a quantitative whole-body read-out may be useful in unclear cases.
Purpose of Review
Statins are routinely applied in patients with coronary artery disease, as they allow significantly to reduce blood cholesterol levels. Although those drugs are endorsed by current guidelines and prescribed routinely, a substantial portion of patients are still statin-intolerant and image-piloted strategies may then be helpful to identify patients that need further intensified treatment, e.g., to initiate treatment with proprotein convertase subtilisin / kexin type 9 inhibitors (PCSK9i). In addition, it has also been advocated that statins exhibit nonlipid, cardio-protective effects including improved cardiac nerve integrity, blood flow, and anti-inflammatory effects in congestive heart failure (HF) patients.
Recent Findings
In subjects after myocardial infarction treated with statins, \(^{123}\)I-metaiodobenzylguanidine (MIBG) scintigraphy has already revealed enhanced cardiac nerve function relative to patients without statins. In addition, all of those aforementioned statin-targeted pathways in HF can be visualized and monitored using dedicated cardiac radiotracers, e.g., \(^{123}\)I-MIBG or \(^{18}\)F-AF78 (for cardiac nerve function), \(^{18}\)F-flurpiridaz (to determine coronary flow) or \(^{68}\)Ga-PentixaFor (to detect inflammation).
Summary
Statins exhibit various cardio-beneficial effects, including improvement of cardiac nerve function, blood flow, and reduction of inflammation, which can all be imaged using dedicated nuclear cardiac radiotracers. This may allow for in vivo monitoring of statin-induced cardioprotection beyond lipid profiling in HF patients.
Aims: Although mortality rate is very high, diagnosis of acute myocarditis remains challenging with conventional tests. We aimed to elucidate the potential role of longitudinal 2-Deoxy-2-\(^{18}\)F-fluoro-D-glucose (\(^{18}\)F-FDG) positron emission tomography (PET) inflammation monitoring in a rat model of experimental autoimmune myocarditis.
Methods and results: Autoimmune myocarditis was induced in Lewis rats by immunizing with porcine cardiac myosin emulsified in complete Freund’s adjuvant. Time course of disease was assessed by longitudinal \(^{18}\)F-FDG PET imaging. A correlative analysis between in- and ex vivo \(^{18}\)F-FDG signalling and macrophage infiltration using CD68 staining was conducted. Finally, immunohistochemistry analysis of the cell-adhesion markers CD34 and CD44 was performed at different disease stages determined by longitudinal \(^{18}\)F-FDG PET imaging. After immunization, myocarditis rats revealed a temporal increase in 18F-FDG uptake (peaked at week 3), which was followed by a rapid decline thereafter. Localization of CD68 positive cells was well correlated with in vivo \(^{18}\)F-FDG PET signalling (R\(^2\) = 0.92) as well as with ex vivo 18F-FDG autoradiography (R\(^2\) = 0.9, P < 0.001, respectively). CD44 positivity was primarily observed at tissue samples obtained at acute phase (i.e. at peak 18F-FDG uptake), while CD34-positive staining areas were predominantly identified in samples harvested at both sub-acute and chronic phases (i.e. at \(^{18}\)F-FDG decrease).
Conclusion: \(^{18}\)F-FDG PET imaging can provide non-invasive serial monitoring of cardiac inflammation in a rat model of acute myocarditis.
PURPOSE:
To evaluate the heart and the Tc-99m-sestamibi biodistribution after statin pretreatment in a rat model of abdominal sepsis.
METHODS:
Twenty-four Wistar rats were randomly distributed into four groups (n=6 per group): 1) sepsis with simvastatin treatment, 2) sepsis with vehicle, 3) sham control with simvastatin and 4) sham control with vehicle. 24 hours after cecal ligation and puncture rats received 1.0MBq of Tc-99m-sestamibi i.v. 30min after, animals were euthanized for ex-vivo tissue counting and myocardium histological analysis.
RESULTS:
Myocardial histologic alterations were not detected 24 hours post-sepsis. There was significantly increased cardiac Tc-99m-sestamibi activity in the sepsis group with simvastatin treatment (1.9\(\pm\)0.3%ID/g, p<0.001) in comparison to the sepsis group+vehicle (1.0\(\pm\)0.2% ID/g), control sham group+ simvastatin (1.2\(\pm\)0.3% ID/g) and control sham group (1.3\(\pm\)0.2% ID/g). Significant Tc-99m-sestamibi activity in liver, kidney and lungs was also detected in the sepsis group treated with simvastatinin comparison to the other groups.
CONCLUSIONS:
Statin treatment altered the biodistribution of Tc-99m-sestamibi with increased cardiac and solid organ activity in rats with abdominal sepsis, while no impact on controls. Increased myocardial tracer activity may be a result of a possible protection effect due to increased tissue perfusion mediated by statins.