Potential of 18 F-FDG-PET as a valuable adjunct to clinical and response assessment in rheumatoid arthritis and seronegative spondyloarthropathies

Molecular imaging of psoriatic arthritis

PURPOSE OF REVIEW

Psoriatic arthritis (PsA) is a chronic inflammatory disease associated with psoriasis. Conventional imaging techniques are used to diagnose the disease and detect long-term structural changes. This review will assess molecular imaging in PsA, to evaluate its potential additive value over conventional and advanced anatomical imaging methods (e.g. ultrasound and MRI).

RECENT FINDINGS

Current research is primarily focused on the molecular imaging technique PET/computed tomography (PET/CT) imaging, in which different tracers have been investigated. Fluorodeoxyglucose (FDG) can visualize disease activity and subclinical inflammation. New tracers targeting inflammatory sites have also been studied, such as FAPI (fibroblast activation protein inhibitor). Moreover, NaF (sodium fluoride) shows promise for imaging of new bone formation. Next to PET/CT, also fluorescence imaging and multispectral optoacoustic tomography have been investigated in the context of PsA.

SUMMARY

Molecular imaging techniques hold promise for early diagnosis, monitoring and management of PsA. Future research is needed to define the role of molecular imaging relative to conventional and anatomical imaging techniques in patient care.

Role of Positron Emission Tomography (PET) in the Diagnosis of Musculoskeletal Disorders

Musculoskeletal disorders (MSDs) represent a broad spectrum of diseases and injuries that significantly affect the musculoskeletal system and impose a considerable burden on global public health. This review focuses on the landscape of MSD diagnoses and emphasizes the high prevalence of these conditions. Additionally, it recognizes the inadequacies of conventional evaluation methods, including radiography and subjective assessments, when addressing their complex pathophysiology. It also attempts to highlight the promise of positron emission tomography (PET), which offers quantitative insights into metabolic and molecular activities before structural changes become evident. The review focuses on key radiotracers, specifically, fluorodeoxyglucose ([18F]-FDG) and sodium fluoride ([18F]-NaF), discussing their efficacy in assessing inflammatory processes and bone metabolism. By exploring the abilities of these advanced imaging modalities, we aim to identify the potential of using PET in the early detection and more accurate assessment of MSDs. Furthermore, we provide a brief outline of directions for future research, advocating for the development of novel radiotracers, the integration of multiple imaging modalities, and the application of artificial intelligence in imaging analysis. This review contributes to a deeper understanding of MSDs and underscores the urgent need for innovative diagnostic strategies to improve patient care and outcomes in musculoskeletal health.

18F-FDG positron emission tomography as a marker of disease activity and treatment response in ankylosing spondylitis and psoriatic arthritis

The ability of 18F-FDG positron emission tomography (PET) to track disease activity and treatment response in patients with Ankylosing Spondylitis (AS) or Psoriatic Arthritis (PsA) remains unclear. Here, we assessed whether 18F-FDG uptake is a marker of disease activity and treatment response in AS or PsA, and explored the ability of 18F-FDG to predict treatment response. Patients with AS (n = 16) or PsA (n = 8) who were scheduled to initiate treatment with biologics were recruited. Participants underwent a clinical evaluation and an 18F-FDG scan prior to therapy initiation. Eleven participants underwent a follow-up 18F-FDG scan 3 months post-treatment. Images were quantified using a composite measure that describes the inflammatory status of the patient. Clinically involved joints/entheses had higher 18F-FDG uptake compared to unaffected areas (median difference > 0.6, p < 0.01). Among patients with AS, pre-treatment 18F-FDG uptake was strongly associated with disease activity (r = 0.65, p = 0.006). Longitudinal 18F-FDG scans demonstrated that decreases in uptake at 3 months were associated to clinical response (βΔgSUVmax > 8.5, p < 0.001). We found no significant association between pre-treatment 18F-FDG uptake and subsequent clinical response. 18F-FDG PET shows potential as a marker of disease activity in AS and PsA, allowing for monitorization of biological treatment efficacy in these patients.

18F-FDG and 18F-NaF PET/CT Global Assessment of Large Joint Inflammation and Bone Turnover in Rheumatoid Arthritis

Rheumatoid arthritis (RA) involves chronic inflammation of synovial joints, causing pain, stiffness, and limited mobility. ¹⁸F-sodium fluoride (NaF) is a PET tracer whose uptake reflects bone turnover, while ¹⁸F-fludeoxyglucose (FDG) shows glucose metabolism and can serve as a marker for inflammation. The aim of this study is to determine the feasibility of calculating the FDG and NaF mean standardized uptake value (SUVmean) in the knee joint, hip joint, and sacroiliac (SI) joint of RA patients and to determine their association with patient characteristics. Prospective FDG-PET/CT as well as NaF-PET/CT imaging was performed on 18 RA patients. The global SUVmean was calculated on FDG-PET/CT and NaF-PET/CT images using a semiautomated CT-based method of segmentation. FDG and NaF uptake were found to be significantly correlated in the knee (r = 0.77, p < 0.001), but not in the hip and SI joints. In the knee, both NaF SUVmean and FDG SUVmean were significantly correlated with body weight, BMI, leptin, and sclerostin levels (p < 0.05). NaF SUVmean was significantly positively correlated with BMI and leptin for both the hip and SI joints (p < 0.05). No significant correlation was observed between either PET parameter and age, height, erythrocyte sedimentation rate (ESR), and interleukins 1 and 6 (IL-1 and IL-6); however, FDG was correlated with inflammatory markers such as C-reactive protein (CRP) and patient global visual analogue scale (VAS-PtGlobal) in some joints. In this study, both FDG and NaF uptake were quantified in large joints of patients with RA using CT segmentation. NaF and FDG SUVmean were correlated with clinical variables related to body weight and adiposity, suggesting that degenerative joint disease may play a larger role in influencing the uptake of these tracers in large joints than RA disease activity. FDG and its correlation with markers of inflammation such as CRP and VAS-PtGlobal suggests that this tracer may serve as a more specific marker for RA disease activity than NaF. Larger prospective and longitudinal data are necessary to gain a better understanding of the roles of FDG and NaF in evaluating RA joint activity in these joints.

Use of Imaging in Axial Spondyloarthritis for Diagnosis and Assessment of Disease Remission in the Year 2022

Medical imaging remains the cornerstone of diagnostics and follow-up of axial spondyloarthritis (axSpA) patients. With the lack of specific biomarkers allowing monitoring of disease activity and progression, clinicians refer to imaging modalities for accurate evaluation of the axSpA burden. Technological advances and increasing availability of modern imaging techniques such as MRI have enabled faster diagnosis of the disease, hence dramatically changed the diagnostic delay and improved the prognosis and functional outcomes for axSpA patients.Active sacroiliitis as visualized by MRI has been widely accepted as a diagnostic tool, and definitions of inflammatory and structural lesions within the axial skeleton have been developed. Recently, it has been acknowledged that bone marrow edema, suggestive of sacroiliitis, is a common finding among non-SpA patients, and could be attributed to mechanical loading or accumulate with age in healthy individuals. Therefore, it is crucial to distinguish between true pathological and concealing imaging findings, not only for diagnostic but also for disease remission purposes. New imaging modalities, aimed for in vivo visualization of specific molecular processes, could be employed to cross-validate findings from techniques used in daily clinical practice. This review critically evaluates the use of different imaging modalities for diagnosis and assessment of disease remission in axSpA in the year 2022.

Adalimumab and sulfasalazine in alleviating sacroiliac and aortic inflammation detected in PET/CT in patients with axial spondyloarthritis: PETSPA

Aim

Inflammatory signals in the sacroiliac (SI) joints and the aorta of patients with axial spondyloarthritis (axSpA) were graded by positron emission tomography/computed tomography (PET/CT) imaging before and after treatment with sulfasalazine (SSZ) or adalimumab (ADA).

Methods

Patients with axSpA, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) ≥ 4, were recruited. Disease‐modifying antirheumatic drug‐naïve patients started SSZ for 12 weeks, whereas those with prestudy treatment with or contraindication to SSZ commenced ADA for 16 weeks. In addition, those patients in the SSZ group with insufficient response commenced ADA for 16 weeks. 18F‐fluorodeoxyglucose PET/CT was performed after inclusion and after treatment with SSZ and ADA. Maximum standardized uptake value (SUVmax) was assessed for the aorta and the SI joints, and maximal target‐to‐blood‐pool ratio (TBRmax) only for the aorta.

Results

Among five SSZ patients, mean ± SD BASDAI was 4.7 ± 1.6 before and 3.5 ± 1.4 after treatment (p = .101). In 13 ADA patients, the BASDAI decreased from 5.4 ± 1.6 to 2.8 ± 2.2 (p < .001). Among the SSZ patients, SUVmax in SI joints decreased from 2.35 ± 0.55 to 1.51 ± 0.22 (−35.8%, p = .029). Aortic TBRmax decreased from 1.59 ± 0.43 to 1.26 ± 0.26 (−33.2%, p = .087). In the ADA patients, SUVmax in the SI joints was 1.92 ± 0.65 before and 1.88 ± 0.54 after treatment (−1.8%, p = .808) and TBRmax in the aorta 1.50 ± 0.60 before and 1.40 ± 0.26 after treatment (−6.7%, p = .485).

Conclusions

Our small open‐label study showed that SSZ may reduce PET‐CT‐detectable inflammation in the SI joints, with a trend towards a reduction in the aorta.

Fluorodeoxyglucose Positron-Emission Tomography/Computed Tomography and Magnetic Resonance Imaging for Adverse Local Tissue Reactions near Metal Implants after Total Hip Arthroplasty: A Preliminary Report

Background

Plain computed tomography (CT) and magnetic resonance imaging (MRI) are useful for diagnosing adverse local tissue reactions after metal-on-metal total hip arthroplasty (THA), but metal artifacts can hamper radiological assessments near the implants. We sought to clarify the usefulness of 18F-fluorodeoxyglucose positron-emission tomography (18F-FDG-PET) CT and MRI in the periprosthetic region, which is difficult to assess after THA due to metal artifacts.

Methods

We performed preoperative 18F-FDG-PET/CT and 18F-FDG-PET/MRI, as well as plain CT and MRI, in 11 metal-on-metal THA patients who underwent revision surgery.

Results

Most patients showed high FDG uptake in the metal artifact areas and pseudotumors in the 18-F-FDG-PET/CT and 18-F-FDG-PET/MRI scans. Intraoperative intra-articular macroscopic and histopathological intra-articular granulation tissue findings were suggestive of adverse local tissue reaction.

Conclusions

The enhanced uptake in the metal artifact areas seemed to reflect adverse local tissue reaction. Therefore, 18F-FDG-PET/CT and 18-F-FDG-PET/MRI can be useful for the auxiliary diagnosis of adverse local tissue reactions after metal-on-metal THA.

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.

Patient Preparation and Patient-related Challenges with FDG-PET/CT in Infectious and Inflammatory Disease

Several factors that influence physiologic 18F-fluorodeoxyglucose (FDG) uptake and general FDG distribution may affect PET/CT imaging in infection and inflammation. The general impact of hyperglycemia on the diagnostic performance of FDG-PET/CT is probably less in infection/inflammation than in malignancy. Patient preparation may reduce physiologic FDG uptake, but recommendations are less established than in malignancy. Local implementation of various patient preparatory measures should reflect the specific patient population and indications. This article outlines some of the challenges with physiologic FDG distribution, focusing on infectious and inflammatory diseases, and potential countermeasures and patient preparation to limit physiologic uptake before scan.

Comparison of the Heel Enthesitis MRI Scoring System (HEMRIS) with clinical enthesitis and local metabolic activity on PET-CT

OBJECTIVE

To compare the Heel Enthesitis MRI Scoring model (HEMRIS) with clinical and PET/CT outcomes in patients with cutaneous psoriasis (Pso), psoriatic arthritis (PsA) or ankylosing spondylitis (AS).

METHODS

This prospective, observational study included 38 patients with Pso, PsA and AS. Patients were included regardless of presence or absence of clinical heel enthesitis. MRI-scans of both ankles and a whole-body 18F-FDG PET/CT were acquired. MRIs were assessed for enthesitis by two independent and blinded observers according to the HEMRIS. A physician, blinded for imaging results, performed clinical evaluations of enthesitis at the Achilles tendon and plantar fascia.

RESULTS

In total, 146 entheses were scored according to the HEMRIS and clinically assessed for enthesitis (6 entheses were clinically affected). In Achilles tendons with clinical enthesitis, the HEMRIS structural damage score was significantly higher, compared to Achilles tendons without clinical enthesitis (respective median scores 1.0 and 0.5; p=0.04). In clinically unaffected entheses, HEMRIS abnormalities occurred in 44/70 (63%) of Achilles tendons and in 23/70 (33%) of plantar fascia. At the Achilles tendon, local metabolic activity measured on PET/CT was weakly associated with the structural (rs=0.25, p=0.03) and total HEMRIS (rs=0.26, p=0.03).

CONCLUSION

This study revealed a high prevalence of subclinical HEMRIS abnormalities and discrepancy between HEMRIS and clinical and PET/CT findings. This may suggest that the HEMRIS is a sensitive method for detection of inflammatory and structural disease of enthesitis at the Achilles tendon and plantar fascia, although the clinical significance of these MRI findings remains to be determined in longitudinal studies.

Potential Applications of PET/CT/MR Imaging in Inflammatory Diseases: Part I: Musculoskeletal and Gastrointestinal Systems

During the past decades, the role of fludeoxyglucose (FDG)-PET and hybrid PET/computed tomography (CT) has been established clinically in the diagnostic workup of a multitude of infectious and inflammatory disorders. In recent years, the fusion of MR imaging to PET has also been increasingly explored, and this may be especially useful in musculoskeletal and gastrointestinal inflammatory diseases due to exceptional soft tissue contrast and reduced radiation dose. This article outlines the current potential for hybrid molecular imaging in the musculoskeletal system and the gastrointestinal tract with special focus on the potential for fused PET/CT/MR imaging.

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.

Comparison of methods of quantifying global synovial metabolic activity with FDG-PET/CT in rheumatoid arthritis

AIM

2-deoxy-2-[¹⁸ F]fluoro-d-glucose positron emission tomography/computed tomography (FDG-PET/CT) can portray increased glycolysis due to inflammation in rheumatoid arthritis (RA). The aim of this study was to evaluate and compare the reliability and construct validity of two methods of quantifying RA disease activity using FDG-PET/CT.

METHOD

Nineteen RA patients and 19 healthy controls matched to sex and age underwent prospective FDG-PET/CT imaging. Metabolic and volumetric metrics were calculated using fixed and adaptive thresholding techniques and partial volume correction. Fixed thresholds segmented regions above average maximum physiological uptake in controls. Differences of means between RA and controls were assessed using t tests, and discrimination was assessed using receiver operating characteristics. Spearman correlation analysis was used to assess associations between FDG-PET/CT measures and clinical assessments of disease activity.

RESULTS

All FDG-PET/CT measures were substantially different and nearly non-overlapping between RA and controls (all P < .001). Area under the curve (AUC) for adaptive threshold parameters ranged from 0.986 to 0.997, and AUC for fixed threshold parameters ranged from 0.898 to 0.945. PET parameters were found to correlate positively with various clinical features, namely C-reactive protein, erythrocyte sedimentation rate, interleukin (IL)-6, IL-1, and swollen joint count.

CONCLUSION

All FDG-PET/CT parameters reflecting global RA disease activity differentiated between RA and controls, indicating high clinical utility to diagnose and assess RA. Adaptive thresholds can be used in a wider setting without control data, but methods utilizing fixed thresholds were more reproducible and more closely associated with indications of inflammation.

Axillary lymph-node metabolic activity assessment on 18F-FDG-PET/CT in rheumatoid arthritis patients treated with biologic therapies

Objective: Recent studies have provided new insights into the role of lymph nodes (LNs) in rheumatoid arthritis (RA). The aim of this study was to evaluate the metabolic activity of the axillary LNs in relation to that of the upper limb joints and the clinical assessment of disease activity in RA patients treated with biologic therapies.Method: ¹⁸F-fluorodeoxyglucose-positron emission tomography/computed tomography (¹⁸F-FDG-PET/CT) scans were acquired for 64 patients with RA at baseline and after 6 months of biologic therapy, and the patients' clinical status was evaluated. The maximum standardized uptake value (SUV_max), metabolic active volume, and total lesion glycolysis (TLG) were used to assess glucose metabolism in the LNs and 12 joints. Clinical evaluations included serum markers and the Disease Activity Score based on 28-joint count-erythrocyte sedimentation rate (DAS28-ESR).Results: Changes in the SUV_max and TLG for the axillary LNs correlated significantly with those of the ipsilateral wrist joints. There was a positive correlation between the changes in the three metabolic parameters of the axillary LNs and the changes in disease activity after treatment. After 6 months of biologic therapy, all metabolic parameters for the axillary LNs in patients with a DAS28-ESR < 3.2 were significantly lower than those of patients with a DAS28-ESR ≥ 3.2.Conclusion: A relationship between the glucose metabolism of the axillary LNs and the ipsilateral wrist joints was demonstrated by the ¹⁸F-FDG-PET/CT parameters. The metabolic activity and active volume of axillary LNs may reflect the therapeutic response to the biologic treatment of RA.

Can Metabolic Pathways Be Therapeutic Targets in Rheumatoid Arthritis?

The metabolic rewiring of tumor cells and immune cells has been viewed as a promising source of novel drug targets. Many of the molecular pathways implicated in rheumatoid arthritis (RA) directly modify synovium metabolism and transform the resident cells, such as the fibroblast-like synoviocytes (FLS), and the synovial tissue macrophages (STM), toward an overproduction of enzymes, which degrade cartilage and bone, and cytokines, which promote immune cell infiltration. Recent studies have shown metabolic changes in stromal and immune cells from RA patients. Metabolic disruption in the synovium provide the opportunity to use in vivo metabolism-based imaging techniques for patient stratification and to monitor treatment response. In addition, these metabolic changes may be therapeutically targetable. Thus, resetting metabolism of the synovial membrane offers additional opportunities for disease modulation and restoration of homeostasis in RA. In fact, rheumatologists already use the antimetabolite methotrexate, a chemotherapy agent, for the treatment of patients with inflammatory arthritis. Metabolic targets that do not compromise systemic homeostasis or corresponding metabolic functions in normal cells could increase the drug armamentarium in rheumatic diseases for combination therapy independent of systemic immunosuppression. This article summarizes what is known about metabolism in synovial tissue cells and highlights chemotherapies that target metabolism as potential future therapeutic strategies for RA.

Clinical Nononcologic Applications of PET/CT and PET/MRI in Musculoskeletal, Orthopedic, and Rheumatologic Imaging

OBJECTIVE

With improvements in PET/CT and PET/MRI over the last decade, as well as increased understanding of the pathophysiology of musculoskeletal diseases, there is an emerging potential for PET as a primary or complementary modality in the management of rheumatologic and orthopedic conditions.

CONCLUSION

We discuss the role of PET/CT and PET/MRI in nononcologic musculoskeletal disorders, including inflammatory and infectious conditions and postoperative complications. There is great potential for an increased role for PET to serve as a primary or complementary modality in the management of orthopedic and rheumatologic disorders.

Hexokinase 2 as a novel selective metabolic target for rheumatoid arthritis

OBJECTIVES

Recent studies indicate that glucose metabolism is altered in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS). Hexokinases (HKs) catalyse the first step in glucose metabolism, and HK2 constitutes the principal HK inducible isoform. We hypothesise that HK2 contributes to the synovial lining hypertrophy and plays a critical role in bone and cartilage damage.

METHODS

HK1 and HK2 expression were determined in RA and osteoarthritis (OA) synovial tissue by immunohistochemistry. RA FLS were transfected with either HK1 or HK2 siRNA, or infected with either adenovirus (ad)-GFP, ad-HK1 or ad-HK2. FLS migration and invasion were assessed. To study the role of HK2 in vivo, 108 particles of ad-HK2 or ad-GFP were injected into the knee of wild-type mice. K/BxN serum transfer arthritis was induced in HK2F/F mice harbouring Col1a1-Cre (HK2Col1), to delete HK2 in non-haematopoietic cells.

RESULTS

HK2 is particular of RA histopathology (9/9 RA; 1/8 OA) and colocalises with FLS markers. Silencing HK2 in RA FLS resulted in a less invasive and migratory phenotype. Consistently, overexpression of HK2 resulted in an increased ability to migrate and invade. It also increased extracellular lactate production. Intra-articular injection of ad-HK2 in normal knees dramatically increased synovial lining thickness, FLS activation and proliferation. HK2 was highly expressed in the synovial lining after K/BxN serum transfer arthritis. HK2Col1 mice significantly showed decreased arthritis severity, bone and cartilage damage.

CONCLUSION

HK2 is specifically expressed in RA synovial lining and regulates FLS aggressive functions. HK2 might be an attractive selective metabolic target safer than global glycolysis for RA treatment.

The Role of Imaging in Diagnosing Axial Spondyloarthritis

Imaging has a central role in the diagnosis, management, and follow-up of patients with axial spondyloarthritis (axSpA). For the early diagnosis of axSpA, magnetic resonance imaging is of utmost relevance. While no novel imaging techniques were developed during the past decade, improvements to the existing modalities have been introduced. This report provides an overview of the applications and limitations of the existing imaging modalities.

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.

Critical Role of Glucose Metabolism in Rheumatoid Arthritis Fibroblast-like Synoviocytes

OBJECTIVE

Up-regulation of glucose metabolism has been implicated not only in tumor cell growth but also in immune cells upon activation. However, little is known about the metabolite profile in rheumatoid arthritis (RA), particularly in fibroblast-like synoviocytes (FLS). This study was undertaken to evaluate whether changes in glucose metabolism in RA FLS could play a role in inflammation and joint damage.

METHODS

Synovium and FLS were obtained from patients with RA and patients with osteoarthritis (OA). The rate of glycolysis after stimulation of FLS with lipopolysaccharide and platelet-derived growth factor BB was measured using glycolysis stress test technology. FLS function was evaluated using a glycolysis inhibitor, 2-deoxy-d-glucose (2-DG). After stimulation of the FLS, a migration scratch assay, MTT assay, and enzyme-linked immunosorbent assay were performed to measure the effect of 2-DG on FLS migration, viability of the FLS, and cytokine secretion, respectively. IRDye 800CW 2-DG was used to assess glucose uptake in the arthritic joints and stromal cells of mice after K/BxN mouse serum transfer. The mice were injected daily, intraperitoneally, with 3-bromopyruvate (BrPa; 5 mg/kg) to assess the effect of inhibition of glycolysis in vivo.

RESULTS

Compared to human OA FLS, the balance between glycolysis and oxidative phosphorylation was shifted toward glycolysis in RA FLS. Glucose transporter 1 (GLUT1) messenger RNA (mRNA) expression correlated with baseline functions of the RA FLS. Glucose deprivation or incubation of the FLS with glycolytic inhibitors impaired cytokine secretion and decreased the rate of proliferation and migration of the cells. In a mouse model of inflammatory arthritis, GLUT1 mRNA expression in the synovial lining cells was observed, and increased levels of glucose uptake and glycolytic gene expression were detected in the stromal compartment of the arthritic mouse joints. Inhibition of glycolysis by BrPa, administered in vivo, significantly decreased the severity of arthritis in this mouse model.

CONCLUSION

Targeting metabolic pathways is a novel approach to understanding the mechanisms of disease. Inhibition of glycolysis may directly modulate synoviocyte-mediated inflammatory functions and could be an effective treatment strategy for arthritis.

Diagnostic value of 18F-fluorodeoxyglucose uptake parameters to differentiate rheumatoid arthritis from other types of arthritis

We aimed evaluate F-fluorodeoxyglucose uptake at major joints for differentiating patients with rheumatoid arthritis (RA) from those with non-RA arthritis using F-fluorodeoxyglucose (FDG)-positron emission tomography (PET).Eighteen patients with RA (13 women; age, 66.8 ± 13.2 years) and 17 patients with non-RA (6 women; age, 50.8 ± 12.5 years) were included. Twelve joints of each patient were examined: shoulder, elbow, wrist, hip, knee, and ankle on both sides. A visual scoring (VS) system was used; quantitative parameters such as maximum standardized uptake value (SUVmax), metabolic active volume (MAV), and total lesion glycolysis (TLG) were evaluated. Total score and value of each parameter were compared between the RA and non-RA groups.Total VS score (mean, 37.7 ± 9.0 vs 21.9 ± 7.2; P < .0001) and SUVmax (mean, 28.1 ± 8.5 vs 17.9 ± 5.8; P < .001) were significantly higher in the RA group than in the non-RA group. A significant between-group difference was also observed with respect to total MAV (608.3 ± 370.7 vs 176.5 ± 217.8; P < .001) and total TLG (1139.3 ± 759.1 vs 289.5 ± 395.4; P < .001). Receiver operating characteristic curve analysis revealed that total VS had the highest area under curve (.92), with sensitivity and specificity of 88.9% and 76.4%, respectively.Quantitative PET parameters could differentiate RA from non-RA. Total VS score, however, appears to be the best convenient qualitative tool for diagnosing RA.

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.

Quantitative Metabolic Volumetric Product on 18Fluorine-2fluoro-2-deoxy-D-glucose-positron Emission Tomography/Computed Tomography in Assessing Treatment Response to Disease-modifying Antirheumatic Drugs in Rheumatoid Arthritis: Multiparametric Analysis Integrating American College of Rheumatology/European League Against Rheumatism Criteria

The purpose of this study was to assess the role of fluoro-2-deoxy-D-glucose-positron emission tomography/computed tomography (FDG-PET/CT) in the evaluation of treatment response evaluation to disease-modifying antirheumatic drug (DMARD) therapy in patients of rheumatoid arthritis (RA). A total of ten patients with proven diagnosis of RA as per the 2010 American College of Rheumatology/European League against Rheumatism (EULAR) criteria were prospectively evaluated. All patients underwent clinical and biochemical evaluation and a baseline FDG-PET/CT with assessment of maximum standardized uptake value and metabolic volumetric product (MVP) values. DMARD therapy was started with a combination of hydroxychloroquine and sulfasalazine. On follow-up at 3 and 6 months, the response to treatment was assessed by clinical, biochemical, and FDG-PET/CT parameters. These parameters were analyzed in a combined manner, and the patients were grouped into 4 categories as per response to DMARD therapy - complete response, good response, mixed response, and no response. Evaluation of treatment response in ten patients at 3^rd month and in nine patients at 6 months showed (a) agreement for MVP, biochemical parameters with clinical symptomatic assessment in all patients, (b) while agreement for EULAR score was noted in only three patients and disagreement in seven patients with clinical symptoms Response EULAR (rEULAR) (0.37) and at 6 months in only three patients and disagreement in six patients, rEULAR (0.52). The correlation factors at 3^rd month and 6^th months were, respectively, as follows: rMVP (0.67 and 0.75), response RA factor (0.54 and 0.74), response erythrocyte sedimentation rate (0.81 and 0.73), response C-reactive protein (0.78 and 0.51), and response anti-cyclic citrullinated peptide antibodies (0.33 and 0.54). The overall response to DMARD therapy at 3 months was assessed with results showing good response by four cases (40%), mixed response by 1 (10%), no response by 5 (50%), and complete response by none (0%). Step-up therapy at 3 months was initiated in four patients showing nonresponse/progression on clinical symptomatic assessment; of these, two patients showed a good response, one mixed response, and the remaining one continued to show nonresponse at 6 months follow-up. One patient who had a minimal response at 3 months on PET-CT (only 5.96% reduction of MVP) was continued on the same DMARD in view of clinical symptomatic good response (at 3 months) but ultimately had disease progression in all scales and worsening of symptom (at 6 months). FDG-PET/CT-based assessment of inflammatory activity noted in the joints of RA with quantitative parameters can be a promising approach for the whole body assessment of RA disease activity and treatment response assessment, especially in inconclusive cases and correlates well with other parameters. MVP can be used as a useful objective and adjunct parameter for assessing response to treatment.

Radionuclide Methods in the Diagnosis of Sacroiliitis in Patients with Spondyloarthritis: An Update

Sacroiliitis, inflammation of the sacroiliac joint (SIJ), is the hallmark of ankylosing spondylitis and spondyloarthritis (SpA) in general. The arsenal of recommended diagnostic modalities for imaging of the SIJ is scanty and, in practice, includes only conventional X-rays and magnetic resonance imaging (MRI). This review suggests that bone scintigraphy, particularly single-photon emission computed tomography (SPECT) with calculation of indices, or SPECT in combination with low-dose computed tomography (CT) can be a sensitive and specific tool for the diagnosis of sacroiliitis and can be used as part of the individualized approach to the diagnosis of axial SpA. In addition, [¹⁸F]fluoride positron emission tomography (PET)/CT imaging and immunoscintigraphy, using labeled monoclonal anti-cytokine antibodies, are promising methods of current scientific interest in this field.

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.

(18)F-FDG and (18)F-NaF PET/CT demonstrate coupling of inflammation and accelerated bone turnover in rheumatoid arthritis

OBJECTIVE

To compare the findings in rheumatoid arthritis (RA)-affected joints between (18)F-fluorodeoxyglucose (FDG) and (18)F-fluoride (NaF) positron emission tomography (PET)/computed tomography (CT).

METHODS

We enrolled twelve RA patients who started a new biologic agent (naïve 9 and switch 3). At entry, both hands were examined by (18)F-FDG PET/CT, (18)F-NaF PET/CT, and X-ray. Intensity of PET signals was determined by standardized uptake value max (SUVmax) in metacarpophalangeal (MCP), proximal interphalangeal (PIP), and ulnar, medial, and radial regions of the wrists. Hand X-rays were evaluated according to the Genant-modified Sharp score at baseline and 6 months.

RESULTS

Both (18)F-FDG and (18)F-NaF accumulated in RA-affected joints. The SUVmax of (18)F-FDG correlated with that of (18)F-NaF in individual joints (r = 0.65), though detail distribution was different between two tracers. (18)F-NaF and (18)F-FDG signals were mainly located in the bone and the surrounding soft tissues, respectively. The sum of SUVmax of (18)F-NaF correlated with disease activity score in 28 joint (DAS28), modified health assessment questionnaire (MHAQ), and radiographic progression. (18)F-FDG and (18)F-NaF signals were associated with the presence of erosions, particularly progressive ones.

CONCLUSION

Our data show that both (18)F-FDG and (18)F-NaF PET signals were associated with RA-affected joints, especially those with ongoing erosive changes.

Evaluation of tocilizumab therapy in patients with rheumatoid arthritis based on FDG-PET/CT

Background

Positron emission tomography (PET) with 2-[18F]-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) can detect the presence of synovitis in rheumatoid arthritis (RA) patients. The aim of this study was to investigate whether the findings of FDG-PET matched the conventional assessments of the disease activity score (DAS) 28, DAS28-CRP, simplified disease activity index (SDAI) and clinical disease activity index (CDAI) in RA patients receiving tocilizumab (TCZ) therapy.

Methods

Seventeen RA patients treated with TCZ were assessed. FDG-PET was performed at baseline and three and six months after the initiation of TCZ therapy. The maximum SUV (SUVmax) of the bilateral shoulder, elbow, wrist, hip, knee and ankle joints were added together (total SUV) and were used to assess the degree of FDG uptake as a representative parameter. The correlations between the ΔSUV and the difference in the clinical parameters at baseline and at each observation period, and the differences in each clinical parameters, were assessed.

Results

The ΔSUV, the differences in the total SUV at baseline and at three/six months after starting treatment positively correlated with the ΔDAS28 (r = 0.615 p = 0.009/ r = 0.775 p < 0.001), ΔDAS28-CRP (r = 0.696, p = 0.002/ r = 0.828, p < 0.001), ΔSDAI (r = 0.652, p = 0.005/ r = 0.686, p = 0.002) and ΔCDAI (r = 0.662, p = 0.004/ r = 0.711, p = 0.001) for each period. The total SUV was significantly decreased at three and six months after the initiation of TCZ (p < 0.05).

Conclusions

A reduction in the FDG uptake was observed at three and six months after the initiation of TCZ therapy. The disease activity estimated on FDG-PET/CT matched the conventional parameters following the TCZ therapy in RA patients.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-393) contains supplementary material, which is available to authorized users.

Is imaging the extremities with PEM feasible? A novel application for a high-resolution positron emission scanner

INTRODUCTION

Positron emission mammography (PEM) has better spatial resolution than positron emission tomography/computed tomography (PET/CT), or PET/CT. We evaluated the feasibility of extremity imaging with PEM using PET as a standard.

METHODS/MATERIALS

Fourteen patients underwent sequential PET/CT and PEM.

RESULTS/DISCUSSION

PEM visualized with equal or improved resolution all of the lesions identified on PET/CT. It often provided additional information such improved uptake localization and also visualized activity in an adjacent structures that was not seen on PET/CT or magnetic resonance imaging. We believe PEM can image the extremities in diseases like melanoma, arthritis and osteomyelitis and patients with metallic hardware.