18F-FDG PET as a Tool to Predict the Clinical Outcome of Infliximab Treatment of Rheumatoid Arthritis: An Explorative Study

What Role Does PET/MRI Play in Musculoskeletal Disorders?

Musculoskeletal disorders of nononcological origin are one of the most frequent reasons for consultation. Patients suffering from musculoskeletal disorders also consult more than once for the same reason. This results in multiple clinical follow-ups after several radiological and serum examinations, the main ones including X-rays targeting the painful anatomical region and inflammatory serum parameters. As part of their work up, patients suffering from musculoskeletal disorders often require multisequence, multi-parameter MRI. PET/MRI is a promising imaging modality for their diagnosis, with the added advantage of being able to be performed in a single visit. PET/MRI is particularly useful for diagnosing osteomyelitis, spondylodiscitis, arthritis, many pediatric pathologies, and a wide range of other musculoskeletal pathologies. PET/MRI is already used to diagnose malignant bone tumors such as osteosarcoma. However, current knowledge of the indications for PET/MRI in nononcological musculoskeletal disorders is based on studies involving only a few patients. This review focuses on the usefulness of PET/MRI for diagnosing nononcological musculoskeletal disorders.

[From conventional to cutting edge imaging in rheumatology]

Imaging instruments, such as conventional X‑ray, ultrasound and magnetic resonance imaging (MRI) are now fully established and highly valued in the care of rheumatology patients. However, the information provided by these imaging modalities in their current form is of limited utility for the prognostic prediction of individual patient outcomes. This article illuminates an important part of the development of imaging and shows that the vision of personalized medicine is becoming increasingly more tangible due to the further development of high-resolution imaging techniques, molecular imaging and artificial intelligence.

Imaging in inflammatory arthritis: progress towards precision medicine

Imaging techniques such as ultrasonography and MRI have gained ground in the diagnosis and management of inflammatory arthritis, as these imaging modalities allow a sensitive assessment of musculoskeletal inflammation and damage. However, these techniques cannot discriminate between disease subsets and are currently unable to deliver an accurate prediction of disease progression and therapeutic response in individual patients. This major shortcoming of today's technology hinders a targeted and personalized patient management approach. Technological advances in the areas of high-resolution imaging (for example, high-resolution peripheral quantitative computed tomography and ultra-high field MRI), functional and molecular-based imaging (such as chemical exchange saturation transfer MRI, positron emission tomography, fluorescence optical imaging, optoacoustic imaging and contrast-enhanced ultrasonography) and artificial intelligence-based data analysis could help to tackle these challenges. These new imaging approaches offer detailed anatomical delineation and an in vivo and non-invasive evaluation of the immunometabolic status of inflammatory reactions, thereby facilitating an in-depth characterization of inflammation. By means of these developments, the aim of earlier diagnosis, enhanced monitoring and, ultimately, a personalized treatment strategy looms closer.

Clinical features of atlantoaxial involvement in patients with rheumatoid arthritis using 18F-fluorodeoxyglucose-positron emission tomography with computed tomography

INTRODUCTION/OBJECTIVES

Cervical spine involvement is one of the most serious complications in rheumatoid arthritis (RA). The study aim was to assess the clinical significance of atlantoaxial (AA) joint involvement detected by ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) with computed tomography (CT) in patients with RA.

METHOD

A prospective cross-sectional study was conducted to evaluate AA joint involvement detected by FDG-PET/CT in consecutive RA patients from December 2017 to February 2022. We investigated the relationship between AA joint involvement and clinical data, including disease activity and patients' cervical symptoms.

RESULTS

Among 48 patients enrolled, abnormal FDG uptake at AA joint was detected in 13 (27%). Rheumatoid factor titre, initial disease activity score 28-erythrocyte sedimentation rate and total standardized uptake value were significantly higher in the 13 patients than in the others (P = 0.004, P < 0.001 and P = 0.001, respectively). All patients with abnormal FDG uptake at AA joint had some cervical symptoms regardless of cervical spine X-ray abnormalities. Neck pain on movement and at rest were more frequent in the 13 patients than in the others (P = 0.001 and P = 0.004, respectively). The most sensitive symptom associated with AA joint involvement was neck pain on movement (sensitivity, 69%), and the most specific symptom was neck pain at rest (specificity, 100%).

CONCLUSIONS

AA joint involvement was commonly observed by FDG-PET/CT in patients with active RA, independent of radiographic findings. Specific cervical symptoms can be important surrogate markers for detection of potential AA synovitis associated with active RA. Key Points • AA joint involvement was frequently seen in RA with high disease activity independent of radiographic findings. • Neck pain was a hallmark of AA joint involvement reflecting disease activity, and resting pain was highly specific.

Update on Imaging of Inflammatory Arthritis and Related Disorders

Arthritis and other rheumatic disorders are very frequent in the general population and responsible for a huge physical and disability burden to affected patients as well as a major cost to the society. Precise evaluation often relies on clinical data only but additional imaging may be required i) for a more objective assessment of the disease status, such as in rheumatoid arthritis (RA) or ankylosing spondyloarthritis (AS), ii) for providing prognostic information and evaluating response to treatment or iii) for establishing diagnosis, in patients with unclear clinical picture, such as polymyalgia rheumatica (PMR) and large-vessel vasculitis (LVV). Besides radiological techniques (x-rays, ultrasound, and MRI), functional and molecular imaging has emerged as a valid tool for this purpose in several disorders. Bone scanning has long been a method of choice but is now more used as a triage tool in patients with unclear complaints, including degenerative disorders (eg osteoarthritis). ¹⁸F-FDG-PET/CT (FDG) proved efficient in assessing the extent of the disease and response to treatment in RA and related disorders, and to provide accurate diagnosis in some systemic disorders, including PMR and LVV. Based on glucose metabolism, FDG-PET/CT is able to show increased metabolism in peripheral cells involved in inflammation (eg neutrophils, lymphocytes or monocytes/macrophages) but also in fibroblasts that proliferate in the pannus. The lack of specificity of FDG is a limitation and many alternative tracers were developed at the preclinical stage or applied in the clinics, especially within clinical trials. They include imaging of macrophages using translocator protein (TSPO), folate-receptors or other targets on activated cells. These new tools will undoubtedly become more and more available in the everyday clinical workup of patients with rheumatisms. Finally, it should be kept in mind that a very simple tracer, ¹⁸F-fluoride is widely more performant in AS than FDG.

Bovine tumor necrosis factor-alpha Increases IL-6, IL-8, and PGE2 in bovine fibroblast-like synoviocytes by metabolic reprogramming

Lameness is a common condition in dairy cattle caused by infectious or noninfectious agents. Joint lesions are the second most common cause of lameness and can be diagnosed in association with the presentation of digit injuries. Fibroblast-like synoviocyte (FLS) are predominant cells of synovia and play a key role in the pathophysiology of joint diseases, thus increasing the expression of proinflammatory mediators. Tumor necrosis factor-alpha (TNF-α) is a potent proinflammatory cytokine involved in cyclooxygenase 2 (COX-2) and proinflammatory cytokine expression in FLS. Previously, TNF-α was demonstrated to increase hypoxia-inducible Factor 1 (HIF-1), a transcription factor that rewires cellular metabolism and increases the expression of interleukin (IL)-6 in bovine FLS (bFLS). Despite this, the proinflammatory effects of TNF-α in bFLS on metabolic reprogramming have been poorly studied. We hypothesized that TNF-α increases glycolysis and in this way controls the expression of IL-6, IL-8, and COX-2 in bFLS. Results first, gas chromatography/mass spectrometry (GC/MS)-based untargeted metabolomics revealed that bTNF-α altered the metabolism of bFLS, increasing glucose, isoleucine, leucine, methionine, valine, tyrosine, and lysine and decreasing malate, fumarate, α-ketoglutarate, stearate, palmitate, laurate, aspartate, and alanine. In addition, metabolic flux analysis using D-glucose-¹³C₆ demonstrated an increase of pyruvate and a reduction in malate and citrate levels, suggesting a decreased flux toward the tricarboxylic acid cycle after bTNF-α stimulation. However, bTNF-α increased lactate dehydrogenase subunit A (LDHA), IL-6, IL-8, IL-1β and COX-2 expression, which was dependent on glycolysis and the PI3K/Akt pathway. The use of FX11 and dichloroacetate (DCA), an inhibitor of LDHA and pyruvate dehydrogenase kinase (PDK) respectively, partially reduced the expression of IL-6. Our results suggest that bTNF-α induces metabolic reprogramming that favors glycolysis in bFLS and increases IL-6, IL-8, IL-1β and COX-2/PGE2.

[18F] FDG uptake in patients with spondyloarthritis: correlation with serum inflammatory biomarker levels

BACKGROUND

We aimed to evaluate the correlation between 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) uptake and disease activity assessed by serum inflammatory biomarker levels in patients with spondyloarthritis (SpA).

METHODS

A total of 36 SpA patients (24 untreated and 12 treated) were examined using FDG positron emission tomography (PET)/computed tomography and classified into axial SpA (axSpA) and peripheral SpA (pSpA). FDG uptake was evaluated in 23 regions of the body and scored as follows: 0 = less than liver uptake; 1 = more than or equal to liver uptake; and 2 = more than or equal to twice liver uptake. A score of 1 or 2 was considered positive. The number of positive regions and the total score were counted in each patient. The maximum standardized uptake value (SUVmax) was calculated for each region, and maximum SUVmax (MaxSUVmax) was used as a representative value. Correlation of PET findings with serum inflammatory biomarker levels, including C-reactive protein (CRP), erythrocyte sedimentation rate, and matrix metalloproteinase 3 (MMP-3), was analyzed.

RESULTS

All but two patients had at least one positive lesion. PET indices correlated significantly with most of the serum inflammatory biomarker levels in untreated SpA, but not in treated SpA. Further, MaxSUVmax, number of positive regions, and total score correlated significantly with CRP (all P values < 0.001), and the number of positive regions (P = 0.012) and total score (P = 0.007) correlated significantly with MMP-3 in untreated pSpA. PET indices did not correlate with any serum inflammatory biomarker level in untreated axSpA.

CONCLUSION

FDG uptake in untreated pSpA correlated significantly with serum inflammatory biomarker levels.

18F-FDG PET molecular imaging: A relevant tool to investigate chronic inflammatory rheumatisms in clinical practice?

18F-Labeled Fluorodeoxyglucose-Positron Emission Tomography (18F-FDG PET) is a molecular imaging tool commonly used in practice for the assessment of many cancers. Thanks to its properties, its use has been progressively extended to numerous inflammatory conditions, including chronic inflammatory rheumatism (CIR) such as rheumatoid arthritis (RA), spondylarthritis (SpAs) and polymyalgia rheumatica (PMR). 18F-FDG PET is currently not recommended for the diagnostic of CIRs. However, this whole-body imaging tool has emerged in clinical practice, providing a general overview of systemic involvement occurring in CIRs. Numerous studies have highlighted the capacity of 18F-FDG PET to detect articular and extra articular involvements in RA and PMR. However, the lack of specificity of 18F-FDG limits its use for diagnosis purpose. Finally, the key question is the definition of the best way to integrate this whole-body imaging tool in the patient's management workflow.

Whole-Body Macrophage Positron Emission Tomography Imaging for Disease Activity Assessment in Early Rheumatoid Arthritis

OBJECTIVE

To investigate the potential of whole-body positron emission tomography/computed tomography (PET/CT) with a macrophage tracer to image arthritis in patients with early rheumatoid arthritis (RA).

METHODS

Thirty-five previously untreated, clinically active patients with early RA underwent whole-body PET/CT scanning with the macrophage tracer (R)-[¹¹C]PK11195 in addition to clinical assessment (Disease Activity Score in 44 joints [DAS44]). Tracer uptake was assessed quantitatively as standardized uptake values (SUVs). In addition, 2 readers blinded to clinical assessment visually scored tracer uptake in joints. Clinical and PET variables were compared using Cohen , linear regression/correlation, and t tests, where appropriate.

RESULTS

All but 1 patient showed enhanced tracer uptake in at least 1 joint. Twelve percent of all joints (171/1470) were visually positive on the PET scan, most frequently the small joints in feet (40%) and hands (37%), followed by wrists (15%). Correlations of visual scores with clinical findings both at patient and joint levels were absent or weak. In contrast, average SUVs in the hands, feet, and whole body showed significant correlations with DAS44 scores, with the best correlation seen in the feet (R² = 0.29, P < 0.01).

CONCLUSION

Clinically active patients with early RA had increased joint uptake of a macrophage PET tracer, especially in the feet. Quantitative, but not visual PET measures of whole body and joint groups, particularly the feet, showed moderate and statistically significant correlations with clinical outcome.

Extra-articular findings with FDG-PET/CT in rheumatoid arthritis patients: more harm than benefit

Objective

Whole-body Positron Emission Tomography with CT-scanning using fluorine-18 fluorodeoxyglucose (18F-FDG) is occasionally used in rheumatoid arthritis (RA) patients to detect arthritis. FDG-PET/CT might also detect malignancies, but the amount of incidental findings and the number of relevant malignant disease that could be missed are currently unknown. We aimed to study the malignancy screening performance of whole-body FDG-PET/CT in longstanding RA patients with low disease activity.

Methods

FDG-PET/CT-scanning was done in the intervention arm of the Dose REduction Strategy of Subcutaneous TNF-inhibitors (DRESS) study, a randomized controlled trial on dose-tapering of biological Disease Modifying Anti-Rheumatic Drugs (bDMARDs). The reference standard was clinical diagnosis of malignancy during the 3 year follow-up of the study. Prevalence of extra-articular abnormalities, follow-up, and treatments were summarized post-hoc.

Results

121 scans were made in 79 patients. Extra-articular abnormalities were found in 59/121 (49%) scans, resulting in additional diagnostic procedures in 21/79 (26.6%) patients. Nine patients (7.4%) were suspected of malignancy, none turned out to be malignant. Six clinical malignancies that developed during follow-up were all negative on baseline FDG-PET/CT.

Conclusion

Whole-body FDG-PET/CT-scanning used in RA patients for imaging of arthritis results in frequent incidental extra-articular findings, while some who apparently had normal scans also developed malignancies.

Trial registration

Netherlands Trial Register, www.trialregister.nl, NL6771

Early prediction of treatment response in rheumatoid arthritis by quantitative macrophage PET

Objective

To determine whether macrophage positron emission tomography (PET)/computed tomography (CT) imaging using (R)-[¹¹C]PK11195 at 0 and 2 weeks is associated with clinical response at 13 weeks in patients with early rheumatoid arthritis (RA).

Methods

Whole-body (R)-[¹¹C]PK11195 PET/CT scans were performed at baseline and after 2 weeks of COBRA-light (combination therapy of methotrexate and prednisone) treatment in 35 patients with clinically active early RA. Clinical assessment (Disease Activity Score of 44 joints (DAS44)) was performed at 0, 2 and 13 weeks of treatment. PET/CT scans were assessed visually by two blinded, experienced readers, and by calculating standardised uptake values (SUVs) for shoulders, elbows, hips, knees, and hand and feet joints. Clinical and PET variables were compared using (multivariate) linear regression.

Results

18 males and 17 females were included (baseline DAS44=3.2 ± 1.0). 171 out of 1470 joints were visually PET positive at baseline, decreasing to 100 joints after 2 weeks. In general, small feet joints showed the highest uptake at baseline, and the largest decrease after 2 weeks (Δ_0-2). Neither baseline nor Δ_0-2 PET measures correlated with DAS44 at 13 weeks. However, at 2 weeks, average SUV of the feet significantly correlated with DAS44 at 13 weeks (R²=0.14, p=0.04). In a multivariable model, DAS44 and average SUV of the feet at 2 weeks showed substantial combined predictive value (combined R²=0.297, p<0.01).

Conclusion

Quantitative macrophage PET assessment of feet joints, together with DAS44, after 2 weeks of COBRA light treatment in patients with early RA correlates with clinical response after 3 months of treatment.

18F-FDG PET-CT scanning in rheumatoid arthritis patients tapering TNFi: reliability, validity and predictive value

OBJECTIVES

To investigate the reliability and validity of 18F-FDG PET-CT scanning (FDG-PET) in rheumatoid arthritis (RA) patients with low disease activity tapering tumor necrosis factor inhibitors (TNFi) and its' predictive value for successful tapering or discontinuation.

METHODS

Patients in the tapering arm of the DRESS study, a randomized controlled trial on TNFi tapering in RA, underwent FDG-PET before tapering (baseline) and after maximal tapering. 48 joints per scan were scored: 1) visually (FDG-avid joint (FAJ) y/n), 2) quantitatively (maximal and mean standardized uptake values (SUVmax and SUVmean)). Interobserver agreement was calculated in 10 patients at baseline. Quantitative and visual FDG-PET scores were investigated for: 1) (multilevel) association with clinical parameters both on joint and patient level and 2) predictive value at baseline and change between baseline and maximal tapering (delta) for successful tapering and discontinuation at 18 months.

RESULTS

79 patients underwent FDG-PET. For performance of identification of FAJs on PET, Cohen's kappa was 0.49 (0.35-0.63). For SUVmax and SUVmean, ICCs were 0.80 (0.77-0.83) and 0.96 (0.9-1.0), respectively. On joint level, swelling was significantly associated with SUVmax and SUVmean (B coefficients with 95%CI 1.0 (0.73-1.35) and 0.2 (0.08-0.32) respectively). On patient level only correlation with acute phase reactants was found. FDG-PET scores were not predictive for successful tapering or discontinuation.

CONCLUSIONS

Quantitative FDG-PET arthritis scoring in RA patients with low disease activity is reliable and has some construct validity. However, no predictive values were found for FDG-PET parameters for successful tapering and/or discontinuation of TNFi.

TNF induces glycolytic shift in fibroblast like synoviocytes via GLUT1 and HIF1A

TNF is a central cytokine in the pathogenesis of rheumatoid arthritis (RA). Elevated level of TNF causes local inflammation that affects immune cells and fibroblast-like synoviocytes (FLS). Nowadays, only 20–30% of patients experience remission after the standard of care therapy—antibodies against TNF. Interestingly, responders show reduced levels of GLUT1 and GAPDH, highlighting a potential link to cellular metabolism. The aim of the study was to investigate whether TNF directly affects the metabolic phenotype of FLS. Real-time respirometry displayed TNF-induced upregulation of glycolysis along with a modest increase of oxidative phosphorylation in FLS from healthy donors. In addition, TNF stimulation enhanced HIF1A and GLUT1 expression. The upregulation of HIF1A and GLUT1 reflects their enriched level in FLS from RA patients (RA-FLS). The inhibition of TAK1, HIF1a and hexokinase deciphered the importance of TNF/TAK1/HIF1A/glycolysis signaling axis. To prove that inhibition of glycolysis reduced the pathogenic phenotype, we showed that 2-deoxyglucose, a hexokinase inhibitor, partially decreased secretion of RA biomarkers. In summary, we identified a direct role of TNF on glycolytic reprogramming of FLS and confirmed the potency of immunometabolism for RA. Further studies are needed to evaluate the therapeutic impact especially regarding non-responder data.

FDG PET-CT in rheumatological diseases

2-deoxy-2[¹⁸F]fluoro-D-glucose (FDG) PET-CT has revolutionized oncological imaging. The cellular processes that make cancer cells visible on FDG PET-CT also occur in a number of inflammatory cells. Exploiting this phenomenon has led to a growth of evidence supporting the use of FDG PET-CT in a wide range of infective and inflammatory diseases. Rheumatological diseases can affect multiple sites within the musculoskeletal system alongside multi-organ extra-articular disease manifestations. Inflammation is central to these diseases, making FDG PET-CT a logical choice. In this review article we describe the various applications of FDG PET-CT in rheumatological diseases using illustrative examples to highlight the beneficial role of FDG PET-CT in each case.

Dissociation between 2-[18F]fluoro-2-deoxy-D-glucose positron emission computed tomography, ultrasound and clinical assessments in patients with non-severe rheumatoid arthritis, including remission

Background

Inflammation of patients joints with severe disease activity of rheumatoid arthritis (RA) has already been visualized and quantified by 2-[¹⁸F]fluoro-2-deoxy-D-glucose positron emission computed tomography ([¹⁸F] FDG PET/CT), but little is known about the metabolic status and its relationship with clinical and ultrasonography (US) metrology in patients with low/moderate activity or in remission.

Methods

Clinical assessments [based on 28-joint disease activity score (DAS₂₈-CRP) and Clinical Disease Activity Index (CDAI)], [¹⁸F] FDG PET/CT, US and X-ray were performed on 63 RA patients classified into remission or low/moderate or severe disease activity groups. PET/CT was visually and then semi-quantitatively analysed by determining the standardized uptake value (SUV) of positive joints.

Results

Of the 1764 joints, 21.1% were tender only, 13.7% swollen only, 27.6% tender or swollen, 7.3% tender and swollen, 20.5% PET/CT-positive and 8.6% US-positive. PET and US measurements were correlated, albeit with poor concordance. The positive predictive value of PET/CT for clinical evaluation (tender and/or swollen) was low, whereas its negative predictive value was high. Highly significant differences were found with the number of PET/CT-positive joints and with cumulative SUV between “severe” and “non-severe” patients (including those in remission and those with low/moderate activity) and not between those classified as “remission” and “non-remission” or “remission” and “low/moderate activity”. Moreover, the correlation between PET/CT measurements and clinical activity was positive only in the CDAI severe disease group. In patients in remission or with low/moderate activity, only 20–30% of joints were PET/CT-negative. In remission, PET/CT and US were positive in different joints, and PET/CT-positive but US-negative joints mainly exhibited RA (38.1%) or normal (49.2%) and not osteoarthritic (12.7%) X-ray patterns.

Conclusions

[¹⁸F] FDG PET/CT was effective at distinguishing patients with severely active disease from other patients. In non-severe RA patients, including those in remission, PET/CT results are discordant from US and clinical observations. A longitudinal analysis is needed to explore the clinical relevance of such infra-clinical disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41927-021-00196-1.

Molecular imaging in MSK radiology: Where are we going?

Musculoskeletal (MSK) pathologies are one of the leading causes of disability worldwide. However, treatment options and understanding of pathogenetic processes are still partially unclear, mainly due to a limited ability in early disease detection and response to therapy assessment. In this scenario, thanks to a strong technological advancement, structural imaging is currently established as the gold-standard of diagnosis in many MSK disorders but each single diagnostic modality (plain films, high-resolution ultrasound, computed tomography and magnetic resonance) still suffer by a low specificity regarding the characterization of inflammatory processes, the quantification of inflammatory activity levels, and the degree of response to therapy. To overcome these limitations, molecular imaging techniques may play a promising role. Starting from the strengths and weaknesses of structural anatomical imaging, the present narrative review aims to highlight the promising role of molecular imaging in the assessment of non-neoplastic MSK diseases with a special focus on its role to monitor treatment response.

Fluorodeoxyglucose PET/CT of Arthritis in Rheumatic Diseases: A Pictorial Review

Rheumatic diseases are various painful conditions that affect joints, bones, cartilage, tendons, ligaments, and muscles. Arthritis is a typical condition of rheumatic disease. Although rheumatoid arthritis is a representative rheumatic disease, various diseases other than rheumatoid arthritis can also affect joints, and differential diagnosis of rheumatic diseases is often difficult owing to the similar clinical manifestations. However, accurate diagnosis is crucial for an appropriate treatment strategy. The utility of fluorine 18 fluorodeoxyglucose (FDG) PET/CT has been established, and it is widely used for assessing malignancies. In addition to accumulating in tumor cells, FDG also accumulates in inflammatory tissue, allowing FDG PET/CT to demonstrate arthritis. PET/CT allows evaluation of whole-body articular and extra-articular lesions in one examination, representing a key advantage over US and MRI, which allow assessment of only a few regions because of their limited field of view. Although FDG PET/CT is sensitive for detecting inflammatory lesions, the uptake itself is nonspecific; therefore, knowledge of characteristic uptake patterns is necessary to narrow the differential diagnosis in rheumatic disease. Furthermore, pathognomonic extra-articular findings such as vasculitis, skin lesions, lymphadenopathy, and chondritis play an important role in achieving accurate diagnosis. The authors present the FDG PET/CT appearances of (a) rheumatoid arthritis and allied disorders (polymyalgia rheumatica, remitting seronegative symmetrical synovitis with pitting edema, adult-onset Still disease), (b) spondyloarthritis (ankylosing spondylitis, psoriatic arthritis, reactive arthritis, inflammatory bowel disease arthritis, SAPHO [synovitis, acne, pustulosis, hyperostosis, and osteitis] syndrome, chronic recurrent multifocal osteomyelitis), and (c) miscellaneous systemic disorders with arthropathy (relapsing polychondritis, multicentric reticulohistiocytosis, amyloidosis, sarcoidosis, hemophilia). ^©RSNA, 2020.

Novel positron emission tomography tracers for imaging of rheumatoid arthritis

Positron emission tomography (PET) is a nuclear imaging modality that relies on visualization of molecular targets in tissues, which is nowadays combined with a structural imaging modality such as computed tomography (CT) or Magnetic Resonance Imaging (MRI) and referred to as hybrid PET imaging. This technique allows to image specific immunological targets in rheumatoid arthritis (RA). Moreover, quantification of the PET signal enables highly sensitive monitoring of therapeutic effects on the molecular target. PET may also aid in stratification of the immuno-phenotype at baseline in order to develop personalized therapy. In this systematic review we will provide an overview of novel PET tracers, investigated in the context of RA, either pre-clinically, or clinically, that specifically visualize immune cells or stromal cells, as well as other factors and processes that contribute to pathology. The potential of these tracers in RA diagnosis, disease monitoring, and prediction of treatment outcome will be discussed. In addition, novel PET tracers established within the field of oncology that may be of use in RA will also be reviewed in order to expand the future opportunities of PET imaging in RA.

Evaluation of the diagnostic performance of 18F-NaF positron emission tomography/computed tomography in patients with suspected ankylosing spondylitis according to the Assessment of SpondyloArthritis International Society criteria

BACKGROUND CONTEXT

Positron emission tomography (PET) is a potential imaging technique for the diagnosis of AS. The visualization of physiological change makes PET potentially suitable for early detection of inflammatory processes, even before anatomical changes occur. Thus, PET might provide specificity via the use of receptor targeting tracers and allows quantification of disease activity in order to accurately monitor therapeutic effects.

PURPOSE

To examine fluorine-18 sodium fluoride (¹⁸F-NaF) PET/computed tomography (PET/CT) findings in patients with inflammatory low back pain and evaluate the utility of this modality in the diagnosis of ankylosing spondylitis (AS) according to the Assessment of SpondyloArthritis International Society (ASAS) criteria.

STUDY DESIGN

Retrospective cohort study.

PATIENTS SAMPLE

Sixty-eight patients who underwent ¹⁸F-NaF PET/CT imaging between April 2015 and April 2017 for evaluation of inflammatory low back pain.

OUTCOME MEASURES

We defined AS-positive lesions on PET/CT as symmetric sacroiliac joint uptake that suggests sacroiliitis, syndesmophytes on the spine, and enthesopathy at any site.

METHODS

All patients were evaluated using the ASAS criteria and assigned to either the AS or the control group. The diagnostic criteria of AS on PET/CT images were defined as ¹⁸F-NaF PET/CT images with at least one of AS-positive findings.

RESULTS

The diagnostic rate of AS was 72.1% among the 68 patients according to the ASAS criteria. The baseline characteristics between the two groups differed significantly in terms of serum C-reactive protein levels and the presence of human leucocyte antigen-B27. Compared to the control group, in the AS group, 39 patients (79.5%) exhibited typical ¹⁸F-NaF PET/CT-positive findings, such as enthesopathy (65.3%, p=.003), syndesmophytes (61.2%, p=.006) and symmetric sacroiliitis (67.3%, p=.001). PET-positive findings had significantly higher area under the curve values than did single ¹⁸F-NaF PET/CT- positive findings, and they had the best performance for concordant diagnosis according to the ASAS criteria.

CONCLUSIONS

¹⁸F-NaF PET/CT yielded significantly different findings between the two groups according to the ASAS criteria and is useful for diagnosing AS.

Quantifying disease activity in rheumatoid arthritis with the TSPO PET ligand 18F-GE-180 and comparison with 18F-FDG and DCE-MRI

Purpose

While the aetiology of rheumatoid arthritis (RA) remains unclear, many of the inflammatory components are well characterised. For diagnosis and therapy evaluation, in vivo insight into these processes would be valuable. Various imaging probes have shown value including dynamic contrast-enhanced (DCE) MRI and PET/CT using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) or tracers targeting the translocator protein (TSPO). To evaluate ¹⁸F-GE-180, a novel TSPO PET tracer, for detecting and quantifying disease activity in RA, we compared ¹⁸F-GE-180 uptake with that of ¹⁸F-FDG and DCE-MRI measures of inflammation.

Methods

Eight RA patients with moderate-to-high, stable disease activity and active disease in at least one wrist were included in this study (NCT02350426). Participants underwent PET/CT examinations with ¹⁸F-GE-180 and ¹⁸F-FDG on separate visits, covering the shoulders and from the pelvis to the feet, including hands and wrists. DCE-MRI was performed on one affected hand. Uptake was compared visually between tracers as judged by an experienced radiologist and quantitatively using the maximum standardised uptake value (SUV_max). Uptake for both tracers was correlated with DCE-MRI parameters of inflammation, including the volume transfer coefficient K^trans using Pearson correlation (r).

Results

PET/CT imaging with ¹⁸F-GE-180 in RA patients showed marked extra-synovial uptake around the affected joints. Overall sensitivity for detecting clinically affected joints was low (14%). ¹⁸F-GE-180 uptake did not or only weakly correlate with DCE-MRI parameters in the wrist (r = 0.09–0.31). ¹⁸F-FDG showed higher sensitivity for detecting symptomatic joints (34%), as well as strong positive correlation with DCE-MRI parameters (SUV_max vs. K^trans: r = 0.92 for wrist; r = 0.68 for metacarpophalangeal joints).

Conclusions

The correlations between DCE-MRI parameters and ¹⁸F-FDG uptake support use of this PET tracer for quantification of inflammatory burden in RA. The TSPO tracer ¹⁸F-GE-180, however, has shown limited use for the investigation of RA due to its poor sensitivity and ability to quantify disease activity in RA.

Multimodal [18 F]FDG PET/CT Is a Direct Readout for Inflammatory Bone Repair: A Longitudinal Study in TNFα Transgenic Mice

In rheumatoid arthritis (RA), chronic joint inflammation leading to bone and cartilage damage is the major cause of functional impairment. Whereas reduction of synovitis and blockade of joint damage can be successfully achieved by disease modifying antirheumatic therapies, bone repair upon therapeutic interventions has only been rarely reported. The aim of this study was to use fluorodeoxyglucose ([¹⁸ F]FDG) and [¹⁸ F]fluoride µPET/CT imaging to monitor systemic inflammatory and destructive bone remodeling processes as well as potential bone repair in an established mouse model of chronic inflammatory, erosive polyarthritis. Therefore, human tumor necrosis factor transgenic (hTNFtg) mice were treated with infliximab, an anti-TNF antibody, for 4 weeks. Before and after treatment period, mice received either [¹⁸ F]FDG, for detecting inflammatory processes, or [¹⁸ F]fluoride, for monitoring bone remodeling processes, for PET scans followed by CT scans. Standardized uptake values (SUV_mean ) were analyzed in various joints and histopathological signs of arthritis, joint damage, and repair were assessed. Longitudinal PET/CT scans revealed a significant decrease in [¹⁸ F]FDG SUVs in affected joints demonstrating complete remission of inflammatory processes due to TNF blockade. In contrast, [¹⁸ F]fluoride SUVs could not discriminate between different severities of bone damage in hTNFtg mice. Repeated in vivo CT images proved a structural reversal of preexisting bone erosions after anti-TNF therapy. Accordingly, histological analysis showed complete resolution of synovial inflammation and healing of bone at sites of former bone erosion. We conclude that in vivo multimodal [¹⁸ F]FDG µPET/CT imaging allows to quantify and monitor inflammation-mediated bone damage and reveals not only reversal of synovitis but also bone repair upon TNF blockade in experimental arthritis. © 2019 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals, Inc.

Development and Validation of an 18 F-Fluorodeoxyglucose-Positron Emission Tomography With Computed Tomography-Based Tool for the Evaluation of Joint Counts and Disease Activity in Patients With Rheumatoid Arthritis

OBJECTIVE

Clinical joint count assessment is important for detecting synovitis but its reliability is a subject of controversy. This study was undertaken to assess the correlation of positron emission tomography (PET)-derived parameters in 68 joints with disease activity and to compare the reliability of joint counts between PET with computed tomography (CT) and clinical assessment in patients with rheumatoid arthritis (RA).

METHODS

We enrolled 91 patients with active RA (69 in a development group and 22 in a validation group) who underwent concurrent ¹⁸ F-fluorodeoxyglucose (¹⁸ F-FDG)-PET-CT and clinical disease activity evaluation. PET-derived parameters were compared with disease activity assessed using clinical joint count parameters. A Disease Activity Score (DAS) using counts of PET-positive joints was developed, and then validation studies were performed in an independent group.

RESULTS

The number of PET-positive joints (of 28 and 68 joints) was significantly correlated with the swollen joint count (SJC) and tender joint count (TJC) and the DAS in 28 joints using the erythrocyte sedimentation rate (DAS28-ESR). Intraobserver and interobserver reliability of PET for the affected joint counts were excellent. Interobserver reliability between nuclear medicine physicians and rheumatologists was good for the SJC and TJC in both 28 joints and 68 joints. After multivariate analyses, including ESR and patient's global assessment of disease activity (PtGA) in addition to PET-derived parameters, the PET/DAS was derived as (0.063 × number of PET-positive joints in 28 joints) + (0.011 × ESR) + (0.030 × PtGA). A significant correlation between the PET/DAS and the DAS28-ESR was confirmed in the validation group (P < 0.001).

CONCLUSION

PET-CT could serve as a sensitive and reliable method in the evaluation of disease activity in RA patients, and may be applicable as a research tool, particularly in clinical trials.

The folate receptor β as a macrophage-mediated imaging and therapeutic target in rheumatoid arthritis

Macrophages play a key role in the pathophysiology of rheumatoid arthritis (RA). Notably, positive correlations have been reported between synovial macrophage infiltration and disease activity as well as therapy outcome in RA patients. Hence, macrophages can serve as an important target for both imaging disease activity and drug delivery in RA. Folate receptor β (FRβ) is a glycosylphosphatidyl (GPI)-anchored plasma membrane protein being expressed on myeloid cells and activated macrophages. FRβ harbors a nanomolar binding affinity for folic acid allowing this receptor to be exploited for RA disease imaging (e.g., folate-conjugated PET tracers) and therapeutic targeting (e.g., folate antagonists and folate-conjugated drugs). This review provides an overview of these emerging applications in RA by summarizing and discussing properties of FRβ, expression of FRβ in relation to macrophage polarization, FRβ-targeted in vivo imaging modalities, and FRβ-directed drug targeting.

In Vivo Molecular Imaging of Musculoskeletal Inflammation and Infection

In vivo molecular imaging detects biologic processes at molecular level and provides diagnostic information at an earlier time point during disease onset or repair. It offers definite advantage over anatomic imaging in terms of improved sensitivity and ability to quantify. Radionuclide molecular imaging has been widely used in clinical practice. This article discusses the role of radionuclide imaging in various infective and inflammatory diseases affecting musculoskeletal system with a focus on PET. It appears that, as more data become available, combined PET/MR imaging could emerge as a front runner in the imaging of musculoskeletal infection and inflammation.

A model of chronic enthesitis and new bone formation characterized by multimodal imaging

Enthesitis is a key feature of several different rheumatic diseases. Its pathophysiology is only partially known due to the lack of access to human tissue and the shortage of reliable animal models for enthesitis. Here, we aimed to develop a model that mimics the effector phase of enthesitis and reliably leads to inflammation and new bone formation. Enthesitis was induced by local injection of monosodium urate (MSU) crystals into the metatarsal entheses of wild-type (WT) or oxidative-burst-deficient (Ncf1**) mice. Quantitative variables of inflammation (edema, swelling) and vascularization (tissue perfusion) were assessed by magnetic resonance imaging (MRI), bone-forming activity by [¹⁸F]-fluoride positron emission tomography (PET), and destruction of cortical bone and new bone formation by computed tomography (CT). Non-invasive imaging was validated by histochemical and histomorphometric analysis. While injection of MSU crystals into WT mice triggered transient mild enthesitis with no new bone formation, Ncf1** mice developed chronic enthesitis accompanied by massive enthesiophytes. In MRI, inflammation and blood flow in the entheses were chronically increased, while PET/CT showed osteoproliferation with enthesiophyte formation. Histochemical analyses showed chronic inflammation, increased vascularization, osteoclast differentiation and bone deposition in the affected entheseal sites. Herein we describe a fast and reliable effector model of chronic enthesitis, which is characterized by a combination of inflammation, vascularization and new bone formation. This model will help to disentangle the molecular pathways involved in the effector phase of enthesitis.

Bone formation in ankylosing spondylitis during anti-tumour necrosis factor therapy imaged by 18F-fluoride positron emission tomography

Objectives

Excessive bone formation is an important hallmark of AS. Recently it has been demonstrated that axial bony lesions in AS patients can be visualized using ¹⁸F-fluoride PET-CT. The aim of this study was to assess whether ¹⁸F-fluoride uptake in clinically active AS patients is related to focal bone formation in spine biopsies and is sensitive to change during anti-TNF treatment.

Methods

Twelve anti-TNF-naïve AS patients [female 7/12; age 39 years (SD 11); BASDAI 5.5 ± 1.1] were included. ¹⁸ F-fluoride PET-CT scans were performed at baseline and in two patients, biopsies were obtained from PET-positive and PET-negative spine lesions. The remaining 10 patients underwent a second ¹⁸F-fluoride PET-CT scan after 12 weeks of anti-TNF treatment. PET scans were scored visually by two blinded expert readers. In addition, ¹⁸F-fluoride uptake was quantified using the standardized uptake value corrected for individual integrated whole blood activity concentration (SUV_AUC). Clinical response to anti-TNF was defined according to a ⩾ 20% improvement in Assessment of SpondyloArthritis international Society criteria at 24 weeks.

Results

At baseline, all patients showed at least one axial PET-positive lesion. Histological analysis of PET-positive lesions in the spine confirmed local osteoid formation. PET-positive lesions were found in the costovertebral joints (43%), facet joints (23%), bridging syndesmophytes (20%) and non-bridging vertebral lesions (14%) and in SI joints (75%). After 12 weeks of anti-TNF treatment, ¹⁸F-fluoride uptake in clinical responders decreased significantly in the costovertebral (mean SUV_AUC −1.0; P < 0.001) and SI joints (mean SUV_AUC −1.2; P = 0.03) in contrast to non-responders.

Conclusions

¹⁸F-fluoride PET-CT identified bone formation, confirmed by histology, in the spine and SI joints of AS patients and demonstrated alterations in bone formation during anti-TNF treatment.

18F- FDG PET/CT joint assessment of early therapeutic response in rheumatoid arthritis patients treated with rituximab

Background

¹⁸F–FDG PET/CT has been proposed in the evaluation of the disease activity in rheumatoid arthritis (RA). The goals of this study were to evaluate the reproducibility of the technique, to compare metabolic parameters to clinical, biological and ultrasonographic parameters before and after treatment and to evaluate whether the early metabolic response was related to the outcome. ¹⁸F- FDG PET/CT of the hands, wrists and knees was obtained in 15 patients with anti-TNFα refractory RA, at baseline and 16 weeks after treatment with rituximab. The number of PET-positive joints (PET+ joints), the cumulative standard uptake value (cSUV) and the composite index (CI) were defined. The composite clinical index DAS₂₈, CRP serum levels and the number of joints positive at ultrasonography (US+ joints) and the cumulative synovial thickness (CST) were also assessed at baseline and week 24.

Results

High interobserver agreement was observed, both at baseline and after treatment. The number of PET+ joints was not correlated with the number of joints tender or swollen. The 3 metabolic parameters were strongly correlated with US, CRP and DAS₂₈ at baseline and with US and CRP (CSUV, CI) at week 16, but no longer with the DAS₂₈ index. The metabolic response based on the change in the visual PET/CT joint analysis predicted the outcome with a high negative predictive value of 91%, with a 91% specificity, and an 86% accuracy.

Conclusions

These preliminary data suggest that ¹⁸F- FDG PET/CT is a reproducible and accurate tool for evaluating disease activity in refractory rheumatoid arthritis and its non-response to rituximab. The correlation obtained with US joint assessment gives relevance to objective diseased joints through imaging techniques.

Molecular Imaging of Inflammatory Arthritis and Related Disorders

Rheumatic disorders comprise a number of diseases that range from benign, mildly symptomatic degenerative disease to severe systemic disorders such as giant-cell vasculitis with dramatic consequences such as acute blindness. The former is relatively common, whereas the latter is rare. In between, commonly encountered disorders such as rheumatoid arthritis and the various spondyloarthritides, with or without peripheral enthesitis, are daily challenges for the caring physician. Clinical evaluation is of utmost importance and is constantly described under the form of specialist guidelines in all parts of the world. Objective assessment of inflammatory arthritis and related disorders is of interest both for the care of the individual patient and for the assessment of the effects of the many novel experimental therapies proposed in this field, most of them being very expensive. High-resolution ultrasound, CT and spectral CT, MRI using various sequences, and molecular imaging using either gamma camera imaging (including SPECT-CT) or PET-CT are all proposed for a better assessment of these diseases. This review focuses on the several nuclear medicine techniques that are or may become useful to helping provide better patient care in this field and is mainly oriented to inflammatory rheumatic disorders, excluding mechanical degenerative diseases.

Focal uptake at the rotator interval or inferior capsule of shoulder on 18F-FDG PET/CT is associated with adhesive capsulitis

OBJECTIVE

To determine if focal increased uptake at the rotator interval (RI) and/or inferior capsule (IC) on¹⁸F-FDG PET/CT ("positive PET") predicts the presence of adhesive capsulitis (AC).

MATERIALS AND METHODS

Three populations were retrospectively examined. Group 1 included 1,137 consecutive ¹⁸F-FDG PET/CT studies and was used to determine the prevalence of focal uptake at the RI or IC. Group 2 included 361 cases from a 10-year period with ¹⁸F-FDG PET/CT and MRI of shoulder performed within 45 days of each other and was used to enrich the study group. Group 3 included 109 randomly selected patients from the same time frame as groups 1 and 2 and was used to generate the control group. The study group consisted of 15 cases from the three groups, which had positive PET findings. PET/CT images were assessed in consensus by two musculoskeletal radiologists. The reference standard for a diagnosis of AC was clinical and was made by review of the medical record by a pain medicine physician.

RESULTS

The prevalence of focal activity at either the RI or IC ("positive PET") was 0.53%. Nine patients had a clinical diagnosis of AC and 15 patients had a positive PET. The sensitivity and specificity of PET for detection of AC was 56% and 87%, respectively. PET/CT had a positive likelihood ratio for AC of 6.3 (95% CI: 2.8-14.6).

CONCLUSIONS

Increased uptake at the RI or IC on PET/CT confers a moderate increase in the likelihood of AC.

Diagnosis and management of rheumatoid arthritis; What is the current role of established and new imaging techniques in clinical practice?

Ultrasound and magnetic resonance imaging (MRI) have become established imaging techniques for the management of rheumatoid arthritis. Several publications have pointed out the advantages of these techniques for a more complete evaluation of the inflammation and structural damage at joint level. Recently new imaging techniques as the positron emission tomography (PET) associated with computed tomography (CT) or MRI scan, and the optical imaging have been introduced in the panorama. This article presents the advantages and limitations of each imaging techniques in light with the recent publications.

B-cell imaging with zirconium-89 labelled rituximab PET-CT at baseline is associated with therapeutic response 24 weeks after initiation of rituximab treatment in rheumatoid arthritis patients

Background

B cells are key players in the pathogenesis of rheumatoid arthritis (RA). Although successful in 50–60% of patients with RA, anti-B-cell therapy given as rituximab could be more efficient by identifying potential responders prior to treatment. Positron emission tomography (PET) using radiolabeled rituximab for B-cell imaging might provide the means to fulfil this unmet clinical need. The objective of this study was to investigate the association between biodistribution of zirconium-89 (⁸⁹Zr)-rituximab on PET-computed tomography (CT) and clinical response in patients with RA.

Methods

We included 20 patients with RA who were starting rituximab treatment. At the first intravenous (i.v.) therapeutic dose, patients were also injected with ⁸⁹Zr-rituximab, followed by PET-CT. European League Against Rheumatism (EULAR) response criteria were applied to determine response at week 24. PET-CT was analyzed visually and quantitatively. Lymph node (LN) biopsies were performed at 0 and 4 weeks to correlate B-cell counts with imaging data.

Results

PET-positive hand joints (range 1–20) were observed in 18/20 patients. Responders had significantly higher ⁸⁹Zr-rituximab uptake in PET-positive hand joints than non-responders (median target-to-background (T/B)) ratios (IQR) were 6.2 (4.0–8.8) vs. 3.1 (2.2–3.9), p = 0.02). At T/B ≥4.0, positive and negative predictive values for clinical response were respectively 90% and 75%. Quantitative ⁸⁹Zr-rituximab hand joint uptake on PET correlated inversely with CD22⁺ B-cell count in LN tissue at 4 weeks of treatment (r = 0.6, p = 0.05). In addition, the CD22⁺ B-cell count in LN correlated positively with quantitative LN PET data at baseline, supporting the specificity of B-cell imaging on PET.

Conclusions

Non-invasive B-cell imaging by ⁸⁹Zr-rituximab PET-CT has promising clinical value to select RA responders to rituximab at baseline. ⁸⁹Zr-rituximab PET-CT may also hold promise for monitoring anti-B-cell therapies in other B-cell driven autoimmune diseases, such as systemic lupus erythematosus and Sjögren’s disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1166-z) contains supplementary material, which is available to authorized users.

Role of 18F-fluorodeoxyglucose Positron Emission Tomography in the Monitoring of Inflammatory Activity in Crohn's Disease

BACKGROUND

Fluorine-fluorodeoxyglucose positron emission tomography (F-FDG PET) has recently attracted interest for the measurement of disease activity in Crohn's disease (CD). The aim of this study was to assess the utility of FDG-PET as a marker of progression of inflammatory activity and its response to treatment in patients with CD.

METHODS

Twenty-two patients with active CD were recruited prospectively to undergo FDG-PET scanning at 2 time points. All 22 index scans were used to assess sensitivity and specificity against a reference standard magnetic resonance imaging measure. Correlations with clinicopathological markers of severity (Harvey-Bradshaw Index, C-reactive protein, and calprotectin) were also performed. Of note, 17/22 patients participated in the longitudinal component and underwent scanning before and 12 weeks after the initiation of anti-tumor necrosis factor alpha therapy. Patients were subcategorized on the basis of a clinically significant response, and responsiveness of the PET measures was assessed using previously described indices. Of note, 5/22 patients took part in the test-retest component of the study and underwent scanning twice within a target interval of 1 week, to assess the reproducibility of the PET measures.

RESULTS

The sensitivity and specificity of F-FDG PET were 88% and 70%, respectively. Standardized uptake value (SUV)-related PET measures correlated significantly both with C-reactive protein and Harvey-Bradshaw Index in cross-sectional and longitudinal analyses. (G)SUVMAX and (G)SUVMEAN demonstrated favorable responsiveness and reliability characteristics (responsiveness ratio of Guyatt >0.80 and % variability <20%) compared with volume-dependent FDG-PET measures. A proportion of the FDG signal (10%-30%) was found to originate from the lumen of diseased segments.

CONCLUSIONS

F-FDG PET may be useful for longitudinal monitoring of inflammatory activity in CD.

Increased 18F-FDG uptake suggests synovial inflammatory reaction with osteoarthritis: preliminary in-vivo results in humans

OBJECTIVE

The aim of this prospective study was to compare the metabolic activity of the knee joints of a group of patients with painful knees clinically (such as recurrent joint pain, joint instability, and functional limitations) consistent with osteoarthritis and those of another group of patients without such complaints, using [F]-2-fluoro-2-deoxy-D-glucose (F-FDG)-PET imaging.

METHODS

A total of 97 patients who participated in either painful joint prosthesis or diabetic foot research studies involving F-FDG-PET scans were asked to complete a knee pain questionnaire. The patients were asked whether they experienced pain in any joint, and if so, which joints were affected.

RESULTS

A total of 18 knee joints without prosthesis were reported to be painful. The maximum standardized uptake values (SUVmax) of the middle joint space and lateral synovial tissue of these 18 knees were measured and compared with those of a set of patients with control asymptomatic knees. The average SUVmax of the middle part of the joint space in the painful knees was 1.35±0.59 compared with an average SUVmax value of 0.86±0.14 in the control group (P=0.0176). The average SUVmax of the synovium in the lateral part of the painful joints was 1.17±0.49 compared with 0.73±0.31 in the control group (P=0.0161).

CONCLUSION

These data indicate that increased F-FDG uptake is associated with knee pain in osteoarthritis patients and that there is a positive relationship between the two parameters.

Scintigraphic detection of TNF-driven inflammation by radiolabelled certolizumab pegol in patients with rheumatoid arthritis and spondyloarthritis

BACKGROUND

Biologicals are the cornerstone for many treatment algorithms in inflammatory arthritis. While tumour necrosis factor (TNF) inhibitors may achieve important responses in ∼50% of patients with rheumatoid arthritis (RA) and spondyloarthritis (SpA), a significant fraction of patients are partial or non-responders. We hypothesised that in vivo assessment of TNF by scintigraphy with 99mTc-radiolabelled certolizumab pegol (CZP) might lead to a more 'evidence-based biological therapy'.

OBJECTIVES

Our goal was to perform a proof-of-concept study of in vivo detection of TNF by immunoscintigraphy of a radiolabelled TNF inhibitor in RA and SpA, and correlate this with clinical, imaging findings and therapeutic outcome.

METHODS

CZP was conjugated with succinimidyl-6-hydrazino-nicotinamide and subsequently radiolabelled with Tc99m. Whole body and static images of hands, feet and sacroiliac joints of 20 patients (5 RA; 15 SpA) were acquired at 3 time points. Immunoscintigraphic findings were scored semiquantitatively. Subsequently, all patients were treated with CZP.

RESULTS

In peripheral joints, clinically affected joints or abnormal ultrasound findings were observed more frequently (p<0.001) in the scintigraphic-positive group. In patients with axial SpA, bone marrow edema on MRI was detected more frequently (p<0.001) in quadrants with tracer uptake. At the patient level, the odds of a joint remaining tender despite 24 weeks of CZP treatment was significantly smaller in joints with clear tracer uptake as compared with those with no uptake (OR=0.42, p=0.04).

CONCLUSIONS

Immunoscintigraphy with radiolabelled CZP demonstrated both axial and peripheral inflammation, and displayed good correlation with clinical features, conventional imaging and therapy response.

TRIAL REGISTRATION NUMBER

NCT01590966; Results.

Clinical value of whole-body PET/CT in patients with active rheumatic diseases

Advanced imaging techniques may enable early diagnosis and monitoring of therapy in various rheumatic diseases. To prevent irreversible tissue damage, inflammatory rheumatic disease must be diagnosed and treated in pre-clinical stages, requiring highly sensitive detection techniques. Positron emission tomography (PET) provides highly sensitive, quantitative imaging at a molecular level, revealing the important pathophysiological processes underlying inflammation. This review provides an overview of the current utility of ¹⁸ F-fluorodeoxyglucose (FDG)-PET/computed tomography (CT) in patients with active rheumatic diseases such as rheumatoid arthritis, spondyloarthritis, polymyalgia rheumatica, adult-onset Still’s disease, relapsing polychondritis, immunoglobulin G4-related disease, large-vessel vasculitis, Wegener’s granulomatosis, polymyositis, and dermatomyositis. We also discuss the role of FDG-PET/CT in the diagnosis and monitoring of these diseases.

[Positron emission tomography with (18)F-FDG in the evaluation of patients with rheumatoid arthritis--a systematic review]

INTRODUCTION

Rheumatoid arthritis (RA) is a disease characterized by inflammation of the synovial membrane. Several authors have investigated the role of positron emission tomography (PET) with fluorine-18 fluorodeoxyglucose ((18)F-FDG) in RA.

OBJECTIVES

To systematically review the current literature on the role of (18)F-FDG PET in the diagnosis, determination of disease activity and assessment of treatment response in patients with RA.

METHODS

Searches were conducted in Medline, Cochrane Library, Lilacs, Pubmed and Scopus in Portuguese, English and Spanish languages, using the keywords "rheumatoid arthritis", "synovitis", "FDG", "PET", "glycolytic metabolism" and "disease activity".

RESULTS

142o articles were initially identified, of which only 40 were related directly to the subject. Twelve original articles and three case reports that met the inclusion criteria were selected.

DISCUSSION

The presence of activated macrophages and fibroblasts in pannus are responsible for the intense periarticular uptake of (18)F-FDG. The uptake patterns do not allow the differential diagnosis with other arthritides. The uptake intensity and the number of joints involved are metabolic parameters of disease activity that correlate well with the composite indices. Longitudinal studies of PET have proven useful in assessing the response to treatment with anti-TNF. When performed early, PET can predict the therapeutic response.

CONCLUSION

Although the actual role of this new technique for the investigation of RA is not yet established, (18)F-FDG PET is a promising tool in determining the activity and prediction of response to treatment of patients with RA.

Detection of Subclinical Synovitis with Macrophage Targeting and Positron Emission Tomography in Patients with Rheumatoid Arthritis without Clinical Arthritis

Objective.

To determine whether macrophage targeting by (R)-11C-PK11195 positron emission tomography (PET) can visualize subclinical joint inflammation in patients with rheumatoid arthritis (RA) without clinical arthritis during or after treatment, with flare as clinical outcome measure.

Methods.

(R)-11C-PK11195 PET and contrast-enhanced magnetic resonance imaging (MRI) of hands/wrists were performed in 29 patients with RA without clinical arthritis. (R)-11C-PK11195 PET uptake (semiquantitative score 0–3) in metacarpophalangeal, proximal interphalangeal, and wrist joints (i.e., 22 joints per patient) was scored and summed to obtain a cumulative PET score (range 0–66). Rheumatoid Arthritis Magnetic Resonance Imaging Scoring (RAMRIS) was performed on similar joints. Synovitis and bone marrow edema scores (> 1) were summed to obtain a cumulative MRI score (range 0–288). Occurrence of flare was determined during 3-year followup.

Results.

Flare was observed in 17/29 patients (59%). (R)-11C-PK11195 PET showed enhanced tracer uptake in 16/29 patients (55%), of which 11 (69%) developed a flare. Highest cumulative PET scores (> 6, n = 3) corresponded with highest cumulative MRI scores (> 39) and were related to development of flare in hands/wrists within 6 months. Cumulative PET scores of patients developing a flare were higher than those of patients without a flare [median (interquartile range) 2 (0–4.5) vs 0 (0–1), p < 0.05]. In contrast, no significant differences were found between cumulative MRI scores of patients with and without a flare.

Conclusion.

(R)-11C-PK11195 PET showed enhanced uptake, pointing to presence of subclinical synovitis in over half of patients without clinical arthritis. (R)-11C-PK11195 PET may be of value for prediction of exacerbation of RA, since cumulative PET scores > 1 were associated with development of flare within 3 years.

Molecular imaging of rheumatoid arthritis: emerging markers, tools, and techniques

Early diagnosis and effective monitoring of rheumatoid arthritis (RA) are important for a positive outcome. Instant treatment often results in faster reduction of inflammation and, as a consequence, less structural damage. Anatomical imaging techniques have been in use for a long time, facilitating diagnosis and monitoring of RA. However, mere imaging of anatomical structures provides little information on the processes preceding changes in synovial tissue, cartilage, and bone. Molecular imaging might facilitate more effective diagnosis and monitoring in addition to providing new information on the disease pathogenesis. A limiting factor in the development of new molecular imaging techniques is the availability of suitable probes. Here, we review which cells and molecules can be targeted in the RA joint and discuss the advances that have been made in imaging of arthritis with a focus on such molecular targets as folate receptor, F4/80, macrophage mannose receptor, E-selectin, intercellular adhesion molecule-1, phosphatidylserine, and matrix metalloproteinases. In addition, we discuss a new tool that is being introduced in the field, namely the use of nanobodies as tracers. Finally, we describe additional molecules displaying specific features in joint inflammation and propose these as potential new molecular imaging targets, more specifically receptor activator of nuclear factor κB and its ligand, chemokine receptors, vascular cell adhesion molecule-1, αVβ₃ integrin, P2X7 receptor, suppression of tumorigenicity 2, dendritic cell-specific transmembrane protein, and osteoclast-stimulatory transmembrane protein.

Evaluation of synovial angiogenesis in patients with rheumatoid arthritis using ⁶⁸Ga-PRGD2 PET/CT: a prospective proof-of-concept cohort study

Background

The study aimed to evaluate the use of positron emission tomography/computed tomography (PET/CT) with ⁶⁸Ga-PRGD2 as the tracer for imaging of synovial angiogenesis in patients with rheumatoid arthritis (RA).

Methods

Twenty untreated active patients with RA underwent ⁶⁸Ga-PRGD2 PET/CT and ¹⁸F-FDG PET/CT before treatment; two patients with osteoarthritis served as controls. Among the 20 patients with RA, 12 repeated the evaluations after 3-month treatment. The image findings were correlated with core variables of disease activity, including the clinical disease activity index (cDAI).

Results

Our findings demonstrated that ⁶⁸Ga-PRGD2 specifically accumulated in the synovia with active inflammation rich in neovasculature with high-level α_vβ₃-integrin expression, but not in the ¹⁸F-FDG-avid inflammatory lymph nodes. In patients with intense ¹⁸F-FDG uptake in muscles caused by arthritic pain, we observed that ⁶⁸Ga-PRGD2 PET/CT was better able to evaluate disease severity than ¹⁸F-FDG PET/CT. Both ⁶⁸Ga-PRGD2 accumulation and ¹⁸F-FDG uptake changed in response to therapeutic intervention, whereas the changes of ⁶⁸Ga-PRGD2, not ¹⁸F-FDG, significantly correlated with clinical measures of changes in the form of cDAI.

Conclusions

This is the first integrin imaging study conducted in patients with RA that preliminarily indicates the effectiveness of the novel method for evaluating synovial angiogenesis.

Clinical trial registration

This study has been registered online at NIH ClinicalTrial.gov (NCT01940926).

The pivotal role of FDG-PET/CT in modern medicine

The technology behind positron emission tomography (PET) and the most widely used tracer, 2-deoxy-2-[18F]fluoro-D-glucose (FDG), were both conceived in the 1970s, but the latest decade has witnessed a rapid emergence of FDG-PET as an effective imaging technique. This is not least due to the emergence of hybrid scanners combining PET with computed tomography (PET/CT). Molecular imaging has enormous potential for advancing biological research and patient care, and FDG-PET/CT is currently the most widely used technology in this domain. In this review, we discuss contemporary applications of FDG-PET and FDG-PET/CT as well as novel developments in quantification and potential future indications including the emerging new modality PET/magnetic resonance imaging.

Clinical translation of molecular imaging agents used in PET studies of cancer

Over recent years, there has been a rapid expansion in our knowledge of the factors that regulate tumor growth; this has resulted in the identification of new therapeutic targets and improvements in the long-term survival of cancer patients. New noninvasive biomarkers of drug targets and pathway modulation in vivo are needed to guide therapy selection and detect drug resistance early so that alternative, more effective treatments can be offered. The translation of new therapeutics into the clinic is disappointingly slow, expensive, and subject to high rates of attrition often occurring at late stages (phase 3) of development. In an attempt to mitigate these delays and failures, there has been resurgence in the development of new molecular imaging probes for studies with positron emission tomography (PET) to characterize tumor biology. In the assessment of therapeutic effects, PET allows imaging of entire tumor burden in a noninvasive repeatable manner. This chapter focuses on the clinical translation of PET imaging agents from bench to bedside. New probes are being used to study a diverse range of processes such as angiogenesis, apoptosis, fatty acid metabolism, and growth factor receptor expression. In the future, validation of these novel imaging probes could allow more innovative therapies to be adapted earlier in the clinic leading to improved patient outcomes.