• large vessel vasculitis
• inflammation
• biomarker
• PET/CT
• FDG
• LVV

Large vessel vasculitides (LVV) are a group of rare cardiovascular diseases with a dysimmune background with a current incidence of about 2 subjects out of 1.000. LVV are systemic and pleomorphic disorders; several organs may be involved and the pathological process may lead to their dysfunction. Patients require numerous clinical and radiological investigations for correct prognostic and therapeutic strategy. Imaging examinations offer a great contribution in the management of the patient suffering from LVV by supporting clinical decisions and providing visual feedback of different disease phenotypes and laboratory tests.

We conducted a single-center retrospective study to investigate the role of [18F]FDG PET/CT and parametric imaging in the evaluation of patients with a positive clinical phenotype for LVV. The aim is to improve diagnostic efficacy and discover new possible applications in long-term patient management, including treatment planning.

We have recruited all patients who were referred with the clinical suspicion of acute onset and/or flair state of LVV to the Center of Nuclear Medicine, Santa Chiara University Hospital of Pisa and completed the [18F]FDG PET/CT examination during the 5-years period of April 2015 to September 2021. All patients’ clinical records were checked to be ensure of diagnostic precision. The study cohort included 185 patients (60% female and 40% male). The mean age of whole group was 66.89±14.34 years. The cohort included three groups – patients with giant cell arteritis, patients with Takayasu's arteritis and patients with secondary vasculitis.

The total 212 [18F]FDG PET/CT examinations of 185 patients were collected. Out of 212 [18F]FDG PET/CT examinations, the 185 were first (baseline) evaluations (87%) while 27 patients (13%) were returned for follow-up clinical and [18F]FDG PET/CT assessment after mean 8.6±11 months. Main indication for [18F]FDG PET/CT assessment were disease flare or acute recurrence. These patients were considered as follow-up patients and their medical history and imaging were collected. The same clinical parameters and imaging analysis used for the positive baseline patients were also applied for all follow-up patients. The qualitative analysis was performed by recording the type of large vessel with the presence of uptake (corresponding to grades 1-2-3 of the Meller’s score). Examined vessels are the same as in the semiquantitative analysis proposed by Slart et al. (2018): thoracic aorta, abdominal aorta, subclavian arteries, axillary arteries, carotid arteries, iliac arteries and femoral arteries. The Total Vascular Score (TVS) was calculated as it represents the sum of Meller’s score of seven different vascular regions. In addiction, the TVS values were divided into four ranges indicating the increasing severity of vascular involvement: minimal (0-4), mild (5-10), moderate (11-15) and severe (16-21).

Repeated measure ANOVA showed that there were no statistical differences in clinical parameters except of fever, which was significantly less frequent (McNemar’s chi-squared=7.7, p<0.05) in follow-up group compared to baseline. Meanwhile TVS was significantly lower (within subject contrast, p<0.05) during follow-up assessment compared to baseline [18F]FDG PET/CT. A borderline significancy in ANA positivity were also found: ANA status seems to decrease in follow-up period compared to baseline (between subject contrast, p=0.06). One can speculate that the immune dysregulation conditioned by circulating autoantibodies might influence self-sustaining parietal inflammation and thus, the TVS. Other interesting finding that becomes apparent after repeated measure ANOVA, is the fact of borderline significant interaction (p<0.05) between steroid therapy and fever, indicating that the effect of steroid therapy on TVS depends on the level of fever, and vice versa.

In conclusion, TVS appears to be a reliable score for stratifying patients with LVV. This semiquantitative score offers valuable information for the clinician both in the initial assessment and during follow-up. TVS allows to manage patients with severe vasculitis in addition to evaluate the response to therapy: in case of non-response or persistence of inflammatory activity, [18F]FDG PET/CT can provide an indication to switch corticosteroid or insert a biological drug.