• Muath A Shraim, Hugo Massé-Alarie, Michael J Farrell, Rocco Cavaleri, Marco L Loggia, and Paul W Hodges.
• The University of Queensland, School of Health & Rehabilitation Sciences, St Lucia, Queensland, Australia.
• Eur J Pain. 2024 Oct 1; 28 (9): 160716261607-1626.

BackgroundChronic 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.MethodsSimultaneous 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.ResultsNeuroinflammatory 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).ConclusionThis preliminary proof-of-concept study suggests that neuroinflammation in back regions of S1/M1 in individuals with nociplastic LBP could plausibly explain some characteristic features of this LBP phenotype.Significance StatementNeuroinflammatory activation localized to sensorimotor areas of the brain in individuals with nociplastic pain might contribute to changes in sensory and motor function and aspects of central sensitization. If cause-effect relationships are established in longitudinal studies, this may direct development of therapies that target neuroinflammatory activation.© 2024 The Author(s). European Journal of Pain published by John Wiley & Sons Ltd on behalf of European Pain Federation ‐ EFIC ®.

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