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

Abstract

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 ([18F]FDG) and [18F]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 [18F]FDG, for detecting inflammatory processes, or [18F]fluoride, for monitoring bone remodeling processes, for PET scans followed by CT scans. Standardized uptake values (SUVmean) 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 [18F]FDG SUVs in affected joints demonstrating complete remission of inflammatory processes due to TNF blockade. In contrast, [18F]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 [18F]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.

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

“…While NaF SUVmean was consistently associated with BMI, FDG SUVmean was more often associated with indicators of RA disease activity such as DAS28-CRP (in the hip) and VAS-PtGlobal (in the hip and SI joint). This is consistent with previous studies, where FDG-PET/CT was able to quantify inflammation-mediated bone damage [ 6 ] and FDG uptake seemed to be a better measure of RA disease activity than NaF SUVmean [ 3 ]. NaF PET/CT has not been used often to study RA but has been the focus of many OA and ankylosing spondylitis studies.…”

“…While an abundance of previous research has focused on imaging with MRI, considering it the “gold standard”, recent studies have been analyzing the usefulness of PET in combination with CT. In fact, when compared to MRI, FDG PET showed promising results in many of the RA studies in both the more commonly studied small joints and the less often studied large joints [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. The aim of this study is to explore the feasibility of calculating the FDG and NaF mean SUV (SUVmean) in the knee joint, hip joint, and sacroiliac (SI) joint of RA patients and to determine the association of these values with clinical characteristics of patients with the disease.…”

Analysis of combined deficiency of interleukin-1 and -6 versus single deficiencies in TNF-mediated arthritis and systemic bone loss

“…µCT scans were performed using a µCT35 (Scanco Medical Solution, Switzerland) with the following settings: 55kVp; 145µA, 8 W; 300 ms, high resolution: trabecular bone microarchitecture, cortical bone density; or medium resolution: talus, ankle, knee joints; reconstruction threshold: 280 (talus, patella, ankle, knee, trabecular bone) or 310 (cortical bone from tibiae) as previously described. 13 For quantitative assessment of local bone damage, bone volume (mm 3 ) was evaluated in patella and talus bones. Trabecular bone variables were assessed in 350 slices of the proximal tibiae (starting 50 slices below the growth plate) and in the lumbar vertebrae body (L4, in 300 slices in between both caudal and cranial growth plates).…”