Il ruolo della 18F FDG-PET/RM nella diagnosi e gestione dei pazienti affetti da vasculiti dei grossi vasi

Aim: The aim of the whole PhD project was to evaluate the feasibility of hybrid 18F-FDG PET/MR in patients with LVV and to better characterize its role in monitor disease activity over time, and predict clinical outcomes. Methods: The overall project comprised two experimental phases. The first one, the feasibility study, was conducted on consecutive LVV patients that were studied with a 18F-FDG PET/MR scan, along with a comparator group consisting of patients with non-metastatic malignancies. For each PET scan, a qualitative analysis and a semi-quantitative measure using the maximum of the standardized uptake value (SUVmax) were performed. SUVmax measurements normalized to the liver uptake were categorized using the Meller’s grading scale. Vessel’s wall thickness (WT) was measured at five fixed points. A comparison of characteristics of FDG-PET and vessel’s wall thickening in patients with clinically active LVV versus clinical remission was conducted. The second one, the follow-up study, was conducted on consecutive patients classified as GCA with LVV involvement (LV-GCA), with a minimum disease duration of 12 months and clinically remitted, who underwent to at least one PET/MR scan between January 2015 and January 2020. For each scan a qualitative summary score (PETVAS) based on global arterial FDG uptake was assessed, along with the Meller’s grading scale. Frequency and characteristics of LV-GCA patients with low-grade inflammation were studied. Predictive value of PET scan was finally evaluated. Results: A total of 55 PET/MR scans were conducted, 32 performed in 23 LVV patients and 23 in controls. All patients were Caucasian, 82% female, median age at PET was 63 [53-65] years and median BMI was 26.2 [21.8-27.3]. We found higher SUVmax compared to controls, in all examined sites, irrespective of clinical disease activity. As expected, when considering only the LVV group, the SUVmax of patients with a qualitatively active disease was significantly higher when compared to qualitatively inactive disease, in all aortic levels considered, except for the max wall thickness (WT) level. In patients with a clinically active disease, the SUVmax was still higher than in patients with a clinical inactive disease for every anatomical level considered, however without reaching a significant value. Mean WT resulted higher in patients than in controls. Unlike metabolic activity, the mean WT did not significantly differ between clinically active or inactive patients in all aortic levels considered. Mean WT positively correlated with age in both cohorts, negatively correlated to disease duration, while no correlation with SUVmax was observed. For the follow-up study, 88 PET scans were performed in 54 LVV-GCA patients, predominantly female (77.8%), aged 68[7,8] years, with a regular BMI (23.9[2.8]) and with a long-standing disease (27[32.6] months). A subsequent PET/MR scan was available in 34 patients (median time between the two scans 9[6.3] months). At first PET examination, low-grade metabolic activity was reported in 68.5% of the cases. LV-GCA patients that showed absence of inflammation had longer disease duration (p=0.034), lower CRP levels (p=0.056) and lower daily prednisone dosage (p=0.029). Change of treatment was more frequent in the high activity group (p<0.001). In the low grade inflammation group, treatment tapering was significantly associated with subsequent PET worsening (OR 12 [1.2-154], p=0.040). In a multivariable model, change of treatment was independently associated with reduced odds of worsening of the subsequent PET scan (OR 0.26 [0.00-0-95], p=0.047). Conclusions: 18F-PET/MR appears to be able to determine the presence of large vessels inflammation. FDG-PET performed in patients with LVV during established clinical remission can identify subsets of patients at risk for future clinical relapse.