This is an experimental medicine, single-centre, observational test-retest study to evaluate Filgotinib's mechanism of analgesic action in RA patients. The investigators hypothesize that Filgotinib's mechanism of analgesic action is determined by at least two factors. The first is related to those CNS sensitization pathways seen in fibromyalgia, specifically DMN-insula brain functional connectivity and insular glutamate. The second is related to peripheral inflammation, specifically joint synovitis, blood cytokines/chemokines and DAN-LIPL functional brain connectivity. The CNS sensitization pain pathways related to fibromyalgia are more quickly modified compared to those related to peripheral inflammation and help explain Filgotinib's rapid onset of effect.