Takayasu arteritis (TA) is a rare, chronic large-vessel granulomatous of unknown etiology, affecting the aorta and its major branches. The disease typically presents at less than 40 years of age and affecting young women. The first goal of TA therapy is prevent progression of inflammatory vascular lesions. Disease Activity (DA) evaluation is currently defined according to National Institutes of Health (NIH) criteria and it is thus very important for therapeutic decision. PET with FDG is a whole body non invasive functional imaging modality that may detect inflammation. The aim of this study is to assess whether the maximum standardized uptake value (SUVmax) of 18F-FDG PET/CT (PET/CT) provides an indication of DA and to compare PET data with magnetic resonance angiography (MRA), NIH criteria, C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR).
A cross-sectional monocentric analysis of 30 patients (pts) with diagnosis of TA was performed at San Raffaele Hospital from September 2010 to April 2014 (26 women and 4 men; mean age: 43 yrs, range: 24-66). All pts underwent PET/CT and MRA examinations, with a median interval of 1 month (range: 0-12 months). All vascular lesions uptake in PET/CT was evaluated both with qualitative (positive-negative) and semi-quantitative (SUVmax) methods. The capability of PET/CT and MRA in detecting active vascular inflammation was compared in all vascular lesions evaluable for dimensions with PET/CT. Correlation of PET/CT versus NIH criteria (active/inactive) and serum biomarkers values as CRP and ESR was also performed.
In 16/30 (53%) pts PET/CT was positive with a median SUVmax of 3.8 (range: 2.1-9.8) also presenting vascular lesions at MRA. In 13/30 (43%) pts PET/CT was negative but showed vascular lesions at MRA. One case was negative at PET/CT and MRA. PET/CT has detected 48 (35%) of the 136 vascular lesions evidenced by MRA. In 4 out of 9 pts (44%) PET/CT (median SUVmax: 3.6, range: 3.3-3.9) matched with NIH criteria for active disease and in 9 out of 21 pts (43%) with clinically inactive disease. In pts with positive PET/CT, median CRP was 21.3 mg/L (range: 0.7-61.4) and median ESR was 43.5 mm/1h (range: 0.6-130.0); while in pts with negative PET/CT, median CRP was 7.6 mg/L (range: 0.0-90.2; p values: 0.285) and median ESR was 22.0 mm/1h (range: 11.0-36.0; p value: 0.071).
These retrospective results indicate that functional (PET) and morphological (MRA) data provide different and synergic information that may facilitate evaluation of DA in TA pts, in addition to NIH criteria. In particular PET data correlate with inflammatory biomarkers and SUVmax value with the presence of inflammation. Further prospective study is absolutely necessary to better define the role of this multimodal assessment for treatment strategy and for identify a new possible prognostic index.

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