Disease activity in rheumatoid arthritis is inversely related to cerebral TSPO binding assessed by [11C]PBR28 positron emission tomography

Reumatoid Arthritis (RA) is an autoimmune disorder characterized by peripheral joint inflammation. Recently, an engagement of the brain immune system has been proposed. The aim with the current investigation was to study the glial cell activation marker translocator protein (TSPO) in a well characterized cohort of RA patients and to relate it to disease activity, peripheral markers of inflammation and autonomic activity. Fifteen RA patients and fifteen healthy controls matched for age, sex and TSPO genotype (rs6971) were included in the study. TSPO was measured using Positron emission tomography (PET) and the radioligand [11C]PBR28. The outcome measure was total distribution volume (VT) estimated using Logan graphical analysis, with grey matter (GM) as the primary region of interest. Additional regions of interest analyses as well as voxel-wise analyses were also performed. Clinical evaluation of disease activity, symptom assessments, serum analyses of cytokines and heart rate variability (HRV) analysis of 24 h ambulatory ECG were performed in all subjects. There were no statistically significant group differences in TSPO binding, either when using the primary outcome VT or when normalizing VT to the lateral occipital cortex (p > 0.05). RA patients had numerically lower VT values than healthy controls (Cohen's D for GM = −0.21). In the RA group, there was a strong negative correlation between [11C]PBR28 VT in GM and disease activity (DAS28)(r = −0.745, p = 0.002, corrected for rs6971 genotype). Higher serum levels of IFNγ and TNF-α were found in RA patients compared to controls (p