Resting state EEG and MEG as biomarkers of chronic pain: a systematic review.

Reliable and objective biomarkers promise to improve the assessment and treatment of chronic pain. Resting-state electroencephalography (EEG) is broadly available, easy-to-use, cost-efficient and, therefore, appealing as a potential biomarker of chronic pain. However, results of EEG studies are heterogeneous. We therefore conducted a systematic review (PROSPERO CRD42021272622) of quantitative resting state EEG and magnetoencephalography (MEG) studies in adult patients suffering from different types of chronic pain. We excluded populations with severe psychiatric or neurologic comorbidity. Risk of bias was assessed using a modified Newcastle-Ottawa Scale. Semi-quantitative data synthesis was conducted using modified albatross plots. We included 76 studies after searching MEDLINE, Web of Science Core Collection, Cochrane Central Register of Controlled Trials and EMBASE. For cross-sectional studies which can serve to develop diagnostic biomarkers, we found higher theta and beta power in chronic pain patients than in healthy participants. For longitudinal studies, which can yield monitoring and/or predictive biomarkers, we found no clear associations of pain relief with M/EEG measures. Likewise, descriptive studies which can yield diagnostic or monitoring biomarkers showed no clear correlations of pain intensity with M/EEG measures. Risk of bias was high in many studies and domains. Together, the present systematic review synthesizes evidence how resting-state M/EEG might serve as a diagnostic biomarker of chronic pain. Beyond, the review might help to guide future M/EEG studies on the development of pain biomarkers.