From the Guidelines
PET-CT is a valuable imaging tool for diagnosing and monitoring Takayasu's arteritis, particularly in early disease stages and for assessing disease activity. It combines functional metabolic information from PET with anatomical details from CT, allowing visualization of vascular inflammation before structural changes occur. In Takayasu's arteritis, active inflammation appears as increased FDG (fluorodeoxyglucose) uptake in the vessel walls of the aorta and its major branches.
Key Points
- PET-CT is especially useful for initial evaluation, detecting subclinical disease, monitoring treatment response, and identifying disease recurrence.
- The procedure involves fasting for 4-6 hours, followed by injection of radioactive FDG and scanning about an hour later.
- Standardized uptake values (SUVs) help quantify inflammation, with higher values indicating more active disease.
- While PET-CT offers advantages over conventional imaging like MRA or CTA in detecting early inflammation, it has limitations including radiation exposure, cost, limited availability, and reduced specificity during immunosuppressive therapy.
- It should be used as part of a comprehensive assessment alongside clinical evaluation, laboratory markers (ESR, CRP), and other imaging modalities for optimal management of Takayasu's arteritis.
Recommendations
- For patients with TAK, noninvasive imaging such as CT angiography, MR angiography, or FDG-PET are recommended over catheter-based dye angiography as a disease activity assessment tool 1.
- For patients with known TAK, regularly scheduled noninvasive imaging in addition to routine clinical assessment is conditionally recommended 1.
- For patients with TAK in apparent clinical remission but with signs of inflammation in new vascular territories on vascular imaging, treatment with immunosuppressive therapy is conditionally recommended 1.
Limitations
- The sensitivity of PET-CT is affected by immunosuppression 1.
- Patients receiving glucocorticoid treatment demonstrate an increase in FDG uptake in the liver, which can lower the diagnostic accuracy when the vessel wall and liver ratio are used 1.
- A diagnostic window of the first 3 days after glucocorticoid treatment initiation to perform FDG-PET/CT is recommended 1.
From the Research
Role of PET-CT in Diagnosing Takayasu's Arteritis
- PET-CT is a useful tool for detecting active inflammation in patients with Takayasu's arteritis, with a sensitivity of 92.6% and specificity of 91.7% for active-phase TA 2.
- The maximum standardized uptake value (max SUV) of FDG-PET/CT provides a quantitative indication of disease activity in Takayasu arteritis cases 2.
- A novel model combining ESR, sum of SUVmean, and IL-2R levels demonstrated superiority in identifying active TA compared with conventional methods 3.
PET-CT in Assessing Disease Activity
- FDG-PET/CT had a sensitivity of 78% and a specificity of 87% for detecting active disease compared with disease activity assessed by the NIH criteria 4.
- The sensitivity of PET/CT scans for evaluating disease activity was 100.0%, specificity was 75.0%, positive predictive value was 87.5%, and negative predictive value was 100.0% compared to NIH criteria in patients with atypical manifestations 5.
- The pooled sensitivity and specificity of 18F-fluorodeoxyglucose-Positron Emission Tomography (FDG-PET) for disease activity was 81% and 74%, respectively 6.
PET-CT in Managing Takayasu's Arteritis
- FDG-PET/CT is useful for detection of active inflammation not only in patients with active TA before treatment but also in relapsing patients receiving immunosuppressive agents 2.
- PET/CT plays a unique role in diagnosing TA patients with atypical manifestations and assisting in evaluating disease activity 5.
- The utility of PET-CT for assessing disease activity remains unclear, with varying results across studies 6.