Neuroinflammatory activation in sensory and motor regions of the cortex is related to sensorimotor function in individuals with low back pain maintained by nociplastic mechanisms : a preliminary proof-of-concept study

Background: Chronic pain involves communication between neural and immune systems. Recent data suggest localization of glial (brain immune cells) activation to the sensorimotor regions of the brain cortex (S1/M1) in chronic low back pain (LBP). As glia perform diverse functions that impact neural function, activation might contribute to sensorimotor changes, particularly in LBP maintained by increased nervous system sensitivity (i.e., nociplastic pain). This preliminary proof-of-concept study aimed to: (i) compare evidence of neuroinflammatory activation in S1/M1 between individuals with and without LBP (and between nociceptive and nociplastic LBP phenotypes), and (ii) evaluate relationships between neuroinflammatory activation and sensorimotor function. Methods: Simultaneous PET-fMRI measured neuroinflammatory activation in functionally defined S1 M1 in pain- free individuals (n = 8) and individuals with chronic LBP (n = 9; nociceptive: n = 4, nociplastic: n = 5). Regions of S1/M1 related to the back were identified using fMRI during motor tasks and thermal stimuli. Sensorimotor measures included single and paired-pulse transcranial magnetic stimulation (TMS) and quantitative sensory testing (QST). Sleep, depression, disability and pain questionnaires were administered. Results: Neuroinflammatory activation was greater in the lower back cortical representation of S1 M1 of the nociplastic LBP group than both nociceptive LBP and pain- free groups. Neuroinflammatory activation in S1/M1 was positively correlated with sensitivity to hot (r = 0.52) and cold (r = 0.55) pain stimuli, poor sleep, depression, disability and BMI, and negatively correlated with intracortical facilitation (r = −0.41). Conclusion: This preliminary proof-of-concept study suggests that neuroinflamation in back regions of S1/M1 in individuals with nociplastic LBP could plausibly explain some characteristic features of this LBP phenotype.