The current study used functional magnetic resonance imaging (fMRI) to directly compare disease-relevant cerebral pain processing in well-characterized patient cohorts of fibromyalgia (FM, nociplastic pain) and rheumatoid arthritis (RA, nociceptive pain). Secondary aims were to identify pain-related cerebral alterations related to the severity of clinical symptoms such as pain intensity, depression and anxiety. Twenty-six FM (without RA-comorbidity) and 31 RA (without FM-comorbidity) patients underwent fMRI while stimulated with subjectively calibrated painful pressures corresponding to a pain sensation of 50 mm on a 100 mm VAS scale. Stimulation sites were at left hand most inflamed proximal interphalangeal joint in RA patients and the left thumbnail in FM patients, two sites that have previously been shown to yield the same brain activation in healthy controls. The current results revealed disease distinct differences during pain modulation in RA and FM. Specifically, in response to painful stimulation, FM compared to RA patients exhibited increased brain activation in bilateral inferior parietal lobe (IPL), left inferior frontal gyrus (IFG)/ventrolateral prefrontal cortex (vlPFC) encapsulating left dorsolateral prefrontal cortex (dlPFC); and right IFG/vlPFC. Whereas, RA compared to FM patients exhibited increased functional connectivity (during painful stimulation) between right and left IPL and sensorimotor network (SMN) and between left IPL and frontoparietal network (FPN). Within the FM group only, anxiety scores positively correlated with pain-related brain activation in left dlPFC and right IFG/vlPFC, which further highlights the complex interaction between affective (i.e. anxiety scores) and sensory (i.e. cerebral pain processing) dimensions in this patient group.Copyright © 2021 International Association for the Study of Pain.
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