The Role of EEG Theta Power and Somatosensory Evoked Potentials in Spinal Cord Stimulator Baseline Responder Selection in Failed Back Surgery Syndrome

Pridgeon, Michael (2025) The Role of EEG Theta Power and Somatosensory Evoked Potentials in Spinal Cord Stimulator Baseline Responder Selection in Failed Back Surgery Syndrome. Doctoral thesis (DClinSci), Manchester Metropolitan University.

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Abstract

The aim of the study was to investigate whether patterns of brain activity measured by quantitative EEG (QEEG) absolute power and somatosensory evoked potentials (SSEPs) could predict the therapeutic response to spinal cord stimulation (SCS) in failed back surgery syndrome (FBSS) patients with chronic neuropathic pain. Twenty-seven patients with FBSS underwent a resting state electroencephalography (EEG) and lower limb somatosensory evoked potentials (SSEP) protocol before SCS and every four days after SCS receiving either high frequency, tonic or burst SCS stimulation. Four patients withdrew after the first trial. Responder’s with ≥50% pain relief from baseline and non-responders <50% pain relief from baseline were compared for each trial. Absolute theta power at the Pz electrode and SSEP P39 was compared to baseline for each stimulation programme and between responder and non-responder patients. A spectral cortical signature for neuropathic pain in FBSS patients was identified. The spectral pattern consisted of raised absolute theta power over the prefrontal, somatosensory, precuneus and lateral occipital cortical regions forming a ring of absolute theta power with concentric reduced theta power over the motor and somatosensory cortices involved with central function. This pattern was associated with high frequency SCS stimulation in 12 out of 16 responders, with tonic SCS stimulation in 10 out of 14 responders and with burst SCS stimulation in 11 out of 15 responders. ROC analyses revealed the baseline pattern had a sensitivity of 85%, specificity of 67% and accuracy of 81% in identifying responders. This suggests that patients identified with this quantitative EEG (QEEG) pattern may no longer need a screening trial with a temporary implant. Significant differences in absolute theta power from baseline were observed with high frequency SCS and tonic SCS using a relative theta power ratio (p<0.05) in responders. The average absolute theta power reduction was lower for high frequency SCS than tonic SCS. High frequency and tonic SCS were observed to modulate the baseline pattern resulting in significant absolute theta power reduction over the somatosensory, precuneus and lateral occipital. Absolute theta power increased over the motor cortex leading to motor cortex reactivation on the Oswestry disability index (ODI). ODI scores associated with physical motor disability improved in patients where the motor cortex was reactivated. Pain Detect scores associated with neuropathic pain symptoms, specifically paraesthesia, crawling and electric shock sensations reduced. In non-responder patients the pattern was absent in 7 out of 11 patients with high frequency SCS, 5 out of 9 patients with tonic SCS and 5 out of 9 patients with burst SCS. Absence of reduced theta power over the motor cortex was the most common feature (n-5) with raised absolute theta power across frontal, somatosensory and precuneus regions. In these patients, absolute theta power was unresponsive to high frequency and tonic SCS with suboptimal pain relief. Despite a very high sensitivity for identifying burst SCS responders with the absolute theta power concentric pattern, no significant changes in absolute theta power or relative theta power ratio were observed in burst SCS responders. Contrastingly high frequency SCS and burst SCS had no significant effects on lower limb SSEP amplitudes in keeping with neuromodulation of Aδ fibres. A significant difference with nonparametric testing was observed for SSEP amplitude reduction with tonic SCS. The identification of this novel spectral pattern may have considerable benefits to SCS pain therapy and associated cost savings.