FDG Uptake by Prosthetic Arterial Grafts in Large Vessel Vasculitis Is Not Specific for Active Disease

Role of 18F-FDG PET/CT in Large Vessel Vasculitis and Polymyalgia Rheumatica

Systemic vasculitides comprise a group of autoimmune diseases affecting blood vessels, including large vessel vasculitis (LVV) and medium-sized vessel vasculitis such as giant cell arteritis (GCA) and Takayasu arteritis (TAK). GCA frequently overlaps with polymyalgia rheumatica (PMR), a rheumatic inflammatory condition affecting bursae, tendons or tendon sheaths, and joints. ¹⁸F-FDG PET/CT plays an important role in the diagnostic work-up of GCA, PMR, and TAK and is increasingly used to monitor treatment response. This continuing education article provides up-to-date guidance on the role of ¹⁸F-FDG PET/CT in patients with LVV, medium-sized vessel vasculitis, and PMR. It provides a general introduction on the clinical presentation and challenges in the diagnostic work-up of LVV and medium-sized vessel vasculitis, with a focus on the 2 major LVV subtypes: GCA, including PMR, and TAK. Next, practice points to perform and interpret the results of ¹⁸F-FDG PET/CT are described in line with the published procedure recommendations. Furthermore, the diagnostic performance and its role for treatment monitoring are discussed, taking into account recent international recommendations for the use of imaging in LVV and medium-sized vessel vasculitis in clinical practice. This is illustrated by several clinically representative PET/CT scan examples. Lastly, knowledge of limitations and pitfalls is essential to understand the role of ¹⁸F-FDG PET/CT in LVV, medium-sized vessel vasculitis, and PMR. Challenges and opportunities, as well as future research and conclusions, are highlighted. Learning objectives provide up-to-date guidance for the role of ¹⁸F-FDG PET/CT in patients with suspected LVV, medium-sized vessel vasculitis, and PMR.

Multimodality imaging of large-vessel vasculitis

Multimodality cardiovascular imaging is an essential component of the clinical management of patients with large-vessel vasculitis (LVV), a chronic, relapsing and remitting inflammatory disease of the aorta and its major branches. Imaging is needed to confirm the initial diagnosis, to survey the extent and severity of arterial involvement, to screen for cardiovascular complications and for subsequent long-term disease monitoring. Indeed, diagnosing LVV can be challenging due to the non-specific nature of the presenting symptoms, which often evoke a broad differential. Identification of disease flares and persistent residual arteritis following conventional treatments for LVV present additional clinical challenges. However, by identifying and tracking arterial inflammation and injury, multimodality imaging can help direct the use of disease-modifying treatments that suppress inflammation and prevent or slow disease progression. Each of the non-invasive imaging modalities can provide unique and complementary information, contributing to different aspects of the overall clinical assessment. This article provides a focused review of the many roles of multimodality imaging in LVV.

Takayasu Arteritis: JACC Focus Seminar 3/4

Takayasu arteritis is a rare idiopathic large-vessel vasculitis that typically affects young women. An early "prepulseless" stage is often missed, associated with nonspecific constitutional symptoms (fever, malaise, and weight loss) and elevated inflammatory markers. Unchecked disease progression leads to the "pulseless" stage, manifest clinically by missing pulses, vascular tenderness, and ischemic symptoms (limb claudication, dizziness, angina, and renovascular hypertension), and is characterized pathologically by arterial wall thickening and stenotic/occlusive lesions or aneurysm formation. Vascular complications (stroke, blindness, heart failure, and aneurysm rupture) could follow unless disease progression is halted by immunosuppressive therapy and critical lesions are palliated by timely endovascular therapy or open surgery. Early diagnosis, effective therapy, and lifelong surveillance for disease activity relapses and vascular disease progression are critical to successful long-term outcomes. The outlook for patients has improved significantly in recent years with the establishment of diagnostic and classification criteria, better investigational modalities, and more effective medical and invasive therapy.

Outcome Measures and Biomarkers for Disease Assessment in Takayasu Arteritis

Takayasu arteritis (TAK) is a less common large vessel vasculitis where histopathology of involved arteries is difficult to access except during open surgical procedures. Assessment of disease activity in TAK, therefore, relies on surrogate measures. Clinical disease activity measures such as the National Institutes of Health (NIH) score, the Disease Extent Index in TAK (DEI.TAK) and the Indian TAK Clinical Activity Score (ITAS2010) inconsistently associate with acute phase reactants (APRs). Computerized tomographic angiography (CTA), magnetic resonance angiography (MRA), or color Doppler Ultrasound (CDUS) enables anatomical characterization of stenosis, dilatation, and vessel wall characteristics. Vascular wall uptake of 18-fluorodeoxyglucose or other ligands using positron emission tomography computerized tomography (PET-CT) helps assess metabolic activity, which reflects disease activity well in a subset of TAK with normal APRs. Angiographic scoring systems to quantitate the extent of vascular involvement in TAK have been developed recently. Erythrocyte sedimentation rate and C-reactive protein have a moderate performance in distinguishing active TAK. Numerous novel biomarkers are under evaluation in TAK. Limited literature suggests a better assessment of active disease by combining APRs, PET-CT, and circulating biomarkers. Validated damage indices and patient-reported outcome measures specific to TAK are lacking. Few biomarkers have been evaluated to reflect vascular damage in TAK and constitute important research agenda.

Large-vessel vasculitis

Large-vessel vasculitis (LVV) manifests as inflammation of the aorta and its major branches and is the most common primary vasculitis in adults. LVV comprises two distinct conditions, giant cell arteritis and Takayasu arteritis, although the phenotypic spectrum of primary LVV is complex. Non-specific symptoms often predominate and so patients with LVV present to a range of health-care providers and settings. Rapid diagnosis, specialist referral and early treatment are key to good patient outcomes. Unfortunately, disease relapse remains common and chronic vascular complications are a source of considerable morbidity. Although accurate monitoring of disease activity is challenging, progress in vascular imaging techniques and the measurement of laboratory biomarkers may facilitate better matching of treatment intensity with disease activity. Further, advances in our understanding of disease pathophysiology have paved the way for novel biologic treatments that target important mediators of disease in both giant cell arteritis and Takayasu arteritis. This work has highlighted the substantial heterogeneity present within LVV and the importance of an individualized therapeutic approach. Future work will focus on understanding the mechanisms of persisting vascular inflammation, which will inform the development of increasingly sophisticated imaging technologies. Together, these will enable better disease prognostication, limit treatment-associated adverse effects, and facilitate targeted development and use of novel therapies.

ACR Appropriateness Criteria® Noncerebral Vasculitis

Noncerebral vasculitis is a wide-range noninfectious inflammatory disorder affecting the vessels. Vasculitides have been categorized based on the vessel size, such as large-vessel vasculitis, medium-vessel vasculitis, and small-vessel vasculitis. In this document, we cover large-vessel vasculitis and medium-vessel vasculitis. Due to the challenges of vessel biopsy, imaging plays a crucial role in diagnosing this entity. While CTA and MRA can both provide anatomical details of the vessel wall, including wall thickness and enhancement in large-vessel vasculitis, FDG-PET/CT can show functional assessment based on the glycolytic activity of inflammatory cells in the inflamed vessels. Given the size of the vessel in medium-vessel vasculitis, invasive arteriography is still a choice for imaging. However, high-resolution CTA images can depict small-caliber aneurysms, and thus can be utilized in the diagnosis of medium-vessel vasculitis. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

IS PET/MRI A RELIABLE TOOL FOR DETECTING VASCULAR ACTIVITY IN TREATED CHILDHOOD-ONSET TAKAYASU'S ARTERITIS (C-TA)? A MULTICENTER STUDY

OBJECTIVES

To assess whether 18F-fluordeoxiglucose-positron emission tomography/magnetic resonance imaging (18F-FDG-PET/MRI) with angiographic sequences can contribute to detecting vessel wall inflammation in patients with childhood-onset Takayasu's arteritis (c-TA) under immunosuppressive therapy.

METHODS

Three-centre cross-sectional study was conducted. 18F-FDG-PET/MRI scans were performed in c-TA patients and in oncologic patients, who served as the control group. Clinical and laboratorial characteristics were also analysed.

RESULTS

Seventeen c-TA patients (65% females) between the ages of 6 and 21 years, mean disease duration of 9.4 years were recruited. Only one patient presented clinical disease activity, and six (35.6%) had increased erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP) levels. The most frequent magnetic resonance angiography (MRA) findings were stenosis and thickening, observed in 82.4% and 70.6% of c-TA patients, respectively. 18F-FDG-PET revealed 18F-FDG uptake higher than the liver in at least one arterial segment in 15 (88.2%) patients in a qualitative analysis and median standardized uptake value (SUVmax) of 3.22 (2.76-3.69) in a semi-quantitative analysis. c-TA patients presented significantly higher SUVmax than oncologic patients (p < 0.001). A positive correlation between SUVmax and CRP levels (Rho=0.528; p=0.029) was evidenced.

CONCLUSION

A state-of-the-art imaging modality was used in c-TA patients and revealed a strong arterial FDG uptake even in patients in apparent remission. We suppose that this finding may represent a silent activity in the vessel wall; however, we cannot exclude the possibility of arterial remodelling. Importantly, a negative imaging scan may help in immunosuppression withdrawal in daily clinical practice.

Carotid contrast-enhanced ultrasonographic assessment of disease activity in Takayasu arteritis

AIMS

To investigate the usefulness of carotid contrast-enhanced ultrasound (CEUS) in assessment of disease activity in patients with Takayasu arteritis (TA).

METHODS AND RESULTS

After screening 219 CEUS records from 124 consecutive patients followed at our clinic between October 2014 and May 2018, data were analysed from 159 carotid CEUS from 86 patients diagnosed with Type I TA. Patients were categorized based on disease activity according to National Institutes of Health criteria into two groups: active disease group (92 CEUS) and non-active disease group (67 CEUS). The enhanced intensity of carotid artery wall: (i) was higher in active disease group than in non-active disease group (3.09 ± 1.67 dB vs. 1.44 ± 1.29 dB, P < 0.0001, respectively); and (ii) had a high predictive value for TA disease activity with area under the curve (AUC) of 86.3% [95% confidence interval (CI) 79.7-92.9], sensitivity of 88.0%, and specificity of 79.1%. The latter AUC was not significantly affected (P > 0.05) when erythrocyte sedimentation rate, C-reactive protein level, or arterial wall thickness were added to assessment of disease activity in TA.

CONCLUSION

Carotid vascularization by CEUS, as sole inflammatory marker, had a high predictive value for disease activity in Type I TA.

PET/CT with 18F-Fluordesoxyglucose in patients with suspected endovascular prosthesis infection

OBJECTIVE

Infection of large vessel prostheses is a rare but critical complication. The aim of this work is to assess the impact of PET/CT with 18F-Fluordesoxyglucose (PET-FDG) on the diagnosis of infection in our environment.

MATERIAL AND METHODS

Thirty-five patients (38 scans) were evaluated for suspected prosthetic infection. A qualitative analysis was performed taking into account the distribution of the radiopharmaceutical, categorizing the studies as positive or negative for infection. Those with focal or multifocal deposits along the vascular prosthesis were considered positive, and negative if a homogeneous and diffuse distribution over the whole prosthesis was observed, or a total absence of uptake. A semi-quantitative analysis was performed using SUVmax and average SUV values, and a metabolic index was calculated (SUVmax of the graft / average SUV of the normal vascular pool).

RESULTS

The PET-FDG study was positive in 20 patients, with a diagnostic accuracy of 84%. The 38 PET-FDG scans performed showed positive capture patterns (focal in 6, multifocal in 15, diffuse in 4) and negative pattern in the remaining 13. The sensitivity, specificity, positive and negative predictive values obtained for the PET-FDG were 95%, 89%, 90% and 94%, and for the AngioTC study 50%, 73%, 73% and 50%, respectively. The area values under the ROC curve were as follows: for the AngioTC 0.642 (not significant), and for the SUVmax values of 0.925 (p<0.005), average SUV of 0.922 (p<0.005) and for the metabolic index of 0.917 (p<0.005).

CONCLUSIONS

The PET-FDG proves to be a tool with high diagnostic accuracy in the infection of vascular prosthesis, both visual analysis according to patterns and semi-quantitative.

Novel Positron Emission Tomography Tracers for Imaging Vascular Inflammation

Purpose of Review

To provide a focused update on recent advances in positron emission tomography (PET) imaging in vascular inflammatory diseases and consider future directions in the field.

Recent Findings

While PET imaging with ¹⁸F-fluorodeoxyglucose (FDG) can provide a useful marker of disease activity in several vascular inflammatory diseases, including atherosclerosis and large-vessel vasculitis, this tracer lacks inflammatory cell specificity and is not a practical solution for imaging the coronary vasculature because of avid background myocardial signal. To overcome these limitations, research is ongoing to identify novel PET tracers that can more accurately track individual components of vascular immune responses. Use of these novel PET tracers could lead to a better understanding of underlying disease mechanisms and help inform the identification and stratification of patients for newly emerging immune-modulatory therapies.

Summary

Future research is needed to realise the true clinical translational value of PET imaging in vascular inflammatory diseases.

SP70-Targeted Imaging for the Early Detection of Lung Adenocarcinoma

NJ001 is a monoclonal antibody that can specifically recognize the SP70 antigen on lung adenocarcinoma cells. The goal of this study was to explore its utility in targeted imaging. Subcutaneous xenograft and orthotopic lung tumor implantation BALB/c mouse models were established. Near-infrared fluorescent CF750-labeled NJ001 was injected into two tumor mouse models. Mice that received orthotopic lung tumor implantation were also injected with NJ001-conjugated nanomagnetic beads intravenously, and then underwent micro-CT scanning. Meanwhile, mice with lung tumor were intravenously injected with normal saline and bare nanomagnetic beads as a control. Fluorescence could be monitored in the mice detected by anti-SP70 fluorescence imaging, which was consistent with tumor burden. Signal intensities detected with SP70-targeted micro-CT scans were greater than those in control mice. More importantly, orthotopic tumor lesions could be found on the fourth week with SP70-targeted imaging, which was 2 weeks earlier than detection in the control. Our results suggest that SP70 is a promising target for molecular imaging, and molecularly targeted imaging with an NJ001-labeled probe could be applied for the early detection of lung adenocarcinoma.

PET/MRI in large-vessel vasculitis: clinical value for diagnosis and assessment of disease activity

Diagnosis of large vessel vasculitis (LVV) and evaluation of its inflammatory activity can be challenging. Our aim was to investigate the value of hybrid positron-emission tomography/magnetic resonance imaging (PET/MRI) in LVV. All consecutive patients with LVV from the Department of Internal Medicine who underwent PET/MRI were included. Three PET/MRI patterns were defined: (i) "inflammatory," with positive PET (>liver uptake) and abnormal MRI (stenosis and/or wall thickening); (ii) "fibrous", negative PET (≤liver uptake) and abnormal MRI; and (iii) "normal". Thirteen patients (10 female; median age: 67-years [range: 23-87]) underwent 18 PET/MRI scans. PET/MRI was performed at diagnosis (n = 4), at relapse (n = 7), or during remission (n = 7). Among the 18 scans, eight (44%) showed an inflammatory pattern and three (17%) a fibrous pattern; the other seven were normal. The distribution of the three patterns did not differ between patients with Takayasu arteritis (TA, n = 10 scans) and those with giant cell arteritis (GCA, n = 8 scans). PET/MRI findings were normal in 2/10 (20%) TA scans vs. 5/8 (62%) GCA scans (p = 0.3). Median SUVmax was 4.7 [2.1-8.6] vs. 2 [1.8-2.6] in patients with active disease vs. remission, respectively (p = 0.003). PET/MRI is a new hybrid imaging modality allowing comprehensive and multimodal analysis of vascular wall inflammation and the vascular lumen. This technique offers promising perspectives for the diagnosis and monitoring of LVV.

Advances in Therapies and Imaging for Systemic Vasculitis

Vasculitis is a systemic disease characterized by immune-mediated injury of blood vessels. Current treatments for vasculitis, such as glucocorticoids and alkylating agents, are associated with significant side effects. Furthermore, the management of both small and large vessel vasculitis is challenging because of a lack of robust markers of disease activity. Recent research has advanced our understanding of the pathogenesis of both small and large vessel vasculitis, and this has led to the development of novel biologic therapies capable of targeting key cytokine and cellular effectors of the inflammatory cascade. In parallel, a diverse range of imaging modalities with the potential to monitor vessel inflammation are emerging. Continued expansion of combined structural and molecular imaging using positron emission tomography with computed tomography or magnetic resonance imaging may soon provide reliable longitudinal tracking of vascular inflammation. In addition, the emergence of radiotracers able to assess macrophage activation and immune checkpoint activity represents an exciting new frontier in imaging vascular inflammation. In the near future, these advances will allow more precise imaging of disease activity enabling clinicians to offer more targeted and individualized patient management.

The Role of Vascular Imaging to Advance Clinical Care and Research in Large-Vessel Vasculitis

Purpose of the Review

The two main forms of large-vessel vasculitis (LVV) are giant cell arteritis (GCA) and Takayasu's arteritis (TAK). Vascular imaging can characterize disease activity and disease extent in LVV. This review critically analyzes the clinical utility of vascular imaging in LVV and highlights how imaging may be incorporated into the management and study of these conditions.

Recent Findings

There are multiple imaging modalities available to assess LVV including ultrasonography, CT angiography (CTA), magnetic resonance angiography (MRA), and ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET). As these techniques are refined, imaging may be increasingly useful to evaluate the cranial arteries and the aorta and its primary branches. In addition, vascular imaging may be useful to monitor disease activity and may have prognostic value to predict future clinical events.

Summary

There are strengths and weaknesses associated with vascular imaging that should be considered when evaluating patients with LVV. Vascular imaging will likely play an increasingly important role in the clinical management of patients and the conduct of research in LVV and may ultimately be incorporated as outcome measures in clinical trials in these conditions.

The long pentraxin PTX3: A prototypical sensor of tissue injury and a regulator of homeostasis

Tissue damage frequently occurs. The immune system senses it and enforces homeostatic responses that lead to regeneration and repair. The synthesis of acute phase molecules is emerging as a crucial event in this program. The prototypic long pentraxin PTX3 orchestrates the recruitment of leukocytes, stabilizes the provisional matrix in order to facilitate leukocyte and stem progenitor cells trafficking, promotes swift and safe clearance of dying cells and of autoantigens, limiting autoimmunity and protecting the vasculature. These non-redundant actions of PTX3 are necessary for the resolution of inflammation. Recent studies have highlighted the mechanisms by which PTX3 adapts the functions of innate immune cells, orchestrates tissue repair and contributes to select the appropriate acquired immune response in various tissues. Conversely, PTX3 continues to be produced in diseases where the inflammatory response does not resolve. It is therefore a valuable biomarker for more precise and personalized stratification of patients, often independently predicting clinical evolution and outcome. There is strong promise for novel therapies based on understanding the mechanisms with which PTX3 plays its homeostatic role, especially in regulating leukocyte migration and the resolution of inflammatory processes.

Usefulness of PET in recognizing and managing vasculitides

PURPOSE OF REVIEW

The aim of this article was to review the recent contributions to the scoring methods of PET in vasculitis as well as to its role in the diagnostic work-up.

RECENT FINDINGS

Both visual and semiquantitative scoring methods can be used to interpret PET scans. PET has been shown to be both sensitive and specific in the diagnosis of large-vessel vasculitis. In addition, it also has a role in predicting vascular complications.

SUMMARY

There is a need to better standardize the scoring methods used to interpret PET scans. In clinical practice, PET is useful to diagnose untreated individuals with suspected large-vessel vasculitis and contributes to identify patients at risk for vascular complications.

18F-FDG PET/CT in the follow-up of large-vessel vasculitis: A study of 37 consecutive patients

OBJECTIVE

¹⁸F-FDG PET/CT has proved to be of potential value for early diagnosis of large-vessel vasculitis (LVV), which frequently involves the aorta. However, its role in the follow-up of these patients has not been well established. Our aim was to evaluate the contribution of ¹⁸F-FDG PET/CT in this clinical situation.

METHODS

This study included 37 consecutive patients (28 women, 66.5 ± 9.9 years) with an initial ¹⁸F-FDG PET/CT positive for LVV and a mean ± standard deviation follow-up PET/CT of 7.5 ± 2.9 months after the initial scan. A semiquantitative analysis of aortic wall uptake was performed calculating the target-to-background ratio (TBR: aortic wall uptake divided by blood pool uptake). The initial and follow-up TBR as well as the clinical and laboratory outcome were compared.

RESULTS

Overall, the mean TBR decreased from 1.7 ± 0.5 at the initial scan to 1.5 ± 0.3 at the time of follow-up (p = 0.0001). In the 21 patients who experienced clinical improvement following therapy the TBR also decreased from 1.8 ± 0.6 to 1.5 ± 0.3 (p = 0.0002). However, in the other 16 patients, in whom the treating physician considered that there was no clinical improvement following therapy, no statistically significant differences in TBR were found when data from the first and the follow-up PET/CT scans were compared (1.6 ± 0.3 versus 1.5 ± 0.3, p = 0.1416). Patients who experienced clinical improvement following therapy showed a nonstatistically significant higher TBR at the time of disease diagnosis (1.8 ± 0.6 versus 1.6 ± 0.3; p = 0.12).

CONCLUSIONS

The results obtained in the present study highlight the impact of ¹⁸F-FDG PET/CT on the management of patients with LVV.