Background Synovitis causes joint destruction in rheumatoid arthritis (RA). While FDG-PET illustrates synovitis sensitively, NaF-PET detects accelerated bone metabolism in osteoplastic lesions of osteoarthrists (OA) as well as osteolytic lesions.
Objectives This study examined the relationship between inflammation and bone damages in joint lesions of RA by using 18F-FDG and 18F-NaF PET/CT of the hands.
Methods Twelve RA patients who started to receive a new biologic agent (naïve 9, switch 3; Etanercept 4, Infliximab 2, Golimumab 2, Tocilizumab 3, Abatacept 1) were enrolled. The bilateral hands were examined by FDG-, NaF-PET/CT and MRI at the entry. Intensity of PET signals was determined by standardized uptake value max (SUVmax) in MCPs, PIPs, and ulnar, medial, and radial regions of the wrist. All joints were also evaluated by power doppler (PD) and gray scale (GS) scores (0-3) in ultrasonography (US). Total score of each parameter was determined by summing up of individual parameters in all joints. Hand X-rays were evaluated according to Genant-modified Sharp score at the baseline and 6 months later. Findings of these imaging modalities and clinical assessments were comparatively analyzed in individual joints.
Results The SUVmax of FDG correlated with that of NaF in individual joints (r=0.62), though detail anatomical localizations were different between them (Figure 1). While NaF signals located on the bone, those of FDG were mainly found in the synovial brusa and tendons On the other hand, NaF accumulation was not accompanied by FDG signals in osteoplastic lesions which were diagnosed as complicated OA in X-ray. Both total FDG and total NaF scores correlated with total PD and total GS of US and DAS 28. Moreover, NaF scores also correlated with HAQ.
Both FDG and NaF SUVmax were significant higher in 44 joints having progression of erosion score than the other 268 joints (FDG; p=0.004, NaF p<0.001). Moreover, total NaF, but not FDG, score was correlated with deterioration of total Sharp score (r=0.66).
Conclusions FDG-PET detects synovistis sensitively, whereas NaF accumulation is more closely associated with bone destructive and plastic lesions. Simultaneous accumulation of the both molecules suggest coupling of inflammation and accelerated bone metabolism in RA joints.
Disclosure of Interest None declared
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