Background/Purpose: Takayasu arteritis (TAK) is a large-vessel vasculitis in which assessment of disease activity is challenging. Recent studies support that 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) is useful for disease activity assessment in TAK. In this study, we examined FDG/PET CT activity in clinically active, persistent and inactive TAK patients according to the physician’s global assessment (PhGA).

Methods: A total of 42 FDG/PET CT images of 31 TAK patients (F/M: 25/6, mean age 41±15 yrs, disease duration 90±71 months) from were evaluated by visual and semiquantitative analysis (vascular SUV_max/liver SUV_max) for vascular inflammation. For the visual analysis using the liver as reference, 18F-FDG uptake was graded from grade 0 to 3. No uptake (grade 0) or any uptake lower than liver (grade 1) in major vessels were regarded as "inactive". Any uptake that is equal to or higher than liver (grade ≥2) was accepted as "active". PhGA, Kerr’s criteria, and ITAS2010 and ITAS-A (both with ESR and CRP) were used for disease activity assessment. Persistent disease is defined as either elevated acute phase reactants (APR) without any clinical signs or symptoms or presence of only one of the Kerr’s criteria regardless of the APR.

Results: At the time of FDG/PET CT imaging 14 (33.3%), 22 (52.4%), and 6 (14.3%) patients were regarded as active, persistent and inactive, respectively. Overall, 24 patients (57.1%) were active by FDG/PET CT visual grading with a median (range) of 2 (1-8) active vascular lesions per patient. Comparison of clinical and FDG/PET CT findings of patients who were regarded as active, persistent and inactive by physician’s assessment revealed higher ITAS2010 and ITAS-A scores, ESR and CRP levels in active and persistent patients (Table). PET-positivity by visual grade was observed in 78.6%, 45.5% and 50% of clinically active, persistent and inactive patients, respectively. In semiquantitative analysis, parallel with the clinical disease activity, an increasing trend was observed in SUV_max (inactive: 2.26, persistent: 3.22, active: 3.44) and SUV_max ratios (inactive: 1.00, persistent: 1.25, active: 1.43). When PET-positive and negative patients were compared, except for APR, no difference in disease activity by ITAS2010 scores were observed.

Conclusion: FDG/PET CT evaluated by visual analysis is useful in demonstrating vascular inflammation and its extent in active TAK patients. However, visual grading of FDG/PET CT is not sufficient enough to differentiate persistent and inactive patients. In these patients semiquantitative analysis should also be considered for further information about vascular inflammation. Further research is also needed to determine whether the increased FDG/PET uptake observed in persistent and inactive patients is associated with actual vascular inflammation that may lead to vascular damage.