gms | German Medical Science

Objective: Chronic neuropathic pain (CNP) may be associated with hyperexcitability of the nociceptive system. Previously, we have shown the recovery of laser evoked potentials (LEP) after 6 months of dorsal root ganglion stimulation (DRGS) therapy of CNP patients. This possibly happened due to the increase in signal to noise ratio resulting from relieving hyperexcitability of the nociceptive system. Therefore, we hypothesize that DRGS may relieve CNP also through a decrease in the broadband cortical gamma power as a reflection of hyperexcitability.

Methods: Here we performed resting-state electroencephalography (EEG) and LEP assessment of 9 patients (2 females) ranged from 36 to 77 years (M = 56.78, SD = 12.80) diagnosed with CNP who received DRGS therapy. The average power spectrum is computed from 5s segments of preprocessed EEG data. EEG channel (C3 or C4) over the sensory-motor cortex contralateral to the limb affected with CNP was selected for the assessment of gamma power before the onset of DRGS and 1 week after DRGS. Additionally, assessment of LEP and ongoing CNP rating were performed before the onset of DRGS and after 1 week of DRGS.

Results: Assessment of resting state gamma power revealed a significant decrease in low gamma power between 30 – 45 Hz (t(8) = 3.076, p = .015) from day 1 (M = 0.614, SD = 0.416) to day 7 (M = 0.248, SD = 0.102) after DRGS. LEP assessment revealed a significant increase (U(8) = -2.67, p = .008) in the LEP amplitude after 1 week (Mdn = 7.60, 95% CI = [7.12, 9.99]) of DRGS when compared to previous DRGS (Mdn = 3.27, 95% CI = [2.75, 3.81]). Recovery of LEP amplitude was accompanied by a significant decrease in CNP rating (U(8) = -2.669, p = .007) after 1 week (Mdn = 2, 95% CI = [1.79, 2.88]) when compared to previous DRGS (Mdn = 7, 95% CI = [6.79, 7.88]). Furthermore, we found a significant correlation of low gamma power (rs(18) = .495, p = .037) with CNP rating.

Conclusion: DRGS therapy for CNP decreased broadband gamma power in addition to LEP recovery and a decrease in CNP rating. Thus, in addition to the recovery of LEP, a decrease in broadband gamma power may be considered as further evidence in favour of a reduction of hyperexcitability of the nociceptive system in response to DRGS therapy as a potential mechanism of CNP relief. Therefore, a positive correlation between gamma power and CNP rating suggests that gamma power may serve as a marker for tuning the DRGS parameters for optimal CNP relief as a clinical application.