Background 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET/CT) is a sensitive imaging tool for large-vessel vasculitis. Although not uniformly accepted, an increased uptake by 18F-FDG PET/CT in large-vessels is accepted to be a sign of active disease in Takayasu’s arteritis (TAK).

Objectives In this study, we aimed to investigate the value of 18F-FDG-PET/CT for clinical assessment in a subset of TAK patients having a persistent acute phase response (APR) without any signs or symptoms of clinical disease activity.

Methods We studied 12 patients with TAK (mean age: 39.2±14.8 years, F/M: 10/2, disease duration: 5.4 years). Patients were clinically inactive (according to the definition of activity by Kerr et al), while categorized as having “persistent” disease activity by physician’s global assessment due only to APR. All patients were under immunosupressive treatments including corticosteroids. The severity of large-vessel 18F-FDG uptake was graded using a four-point scale from grade 0 (no uptake present) to grade III (high-grade: uptake higher than liver). Any uptake in major vessels with a grade ≥2 was accepted to be “active.”

Results Mean ESR was 55.5 (30-86) mm/h and mean CRP was 29.6 (7.7-90) mg/L. Active vasculitic lessions were observed by 18F-FDG-PET/CT in 8 of 12 (66%) of the study group, with a mean number of 2.6 (1-4) active vascular lesions. Arcus aorta was involved in 25%, ascending aorta in 20%, right brachiocephalic artery in 20%, descending aorta in 15%, abdominal aorta in 10% and left and right subclavian arteries in 5% each of the investigated vessels. A step-up treatment change was decided in 7 patients according to 18F-FDG-PET/CT results.

Conclusions We observed increased 18F-FDG uptake in the majority of TAK patients with an increased APR, but clinically silent disease. 18F-FDG-PET/CT showed the presence and localisation of active vascular inflammation in the aorta and its branches. Although specificity of observed lesions are not clear, 18F-FDG-PET/CT imaging may influence physician’s assessment of clinical activity and treatment choices in TAK.

Disclosure of Interest: None Declared