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Restoration of laser evoked potentials (LEP) in patients receiving dorsal root ganglion (DRG) stimulation

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RESTORATION OF LASER EVOKED POTENTIALS (LEP) IN PATIENTS RECEIVING DORSAL ROOT GANGLION (DRG) STIMULATION


Marcos Fortunato de Barros Filho1, Bankim S. Chander2, Matthias H. Morgalla1, Surjo Soekadar2, Marcos Tatagiba1, Luis Garcia-Larrea3, Daniel Ciampi de Andrade4, Guilherme Lepski1,4

1. Department of Neurosurgery, University Hospital of Tuebingen, Germany

2. Applied Neurotechnology Lab, Department of Psychiatry and Psychotherapy, University Hospital of Tübingen, Germany

3. INSERM Central Integration of Pain (U879), University of Lyon, France

4. Department of Neurology, University of São Paulo, Brazil

 

INTRODUCTION

 

Chronic neuropathic pain results from a lesion or disease affecting the somatosensory system (1). A recent systematic review has revealed a prevalence rate of neuropathic pain in the general population from 6.9% to 10% (2). The treatment of chronic neuropathic pain involves a multidisciplinary approach. Neuromodulation is the last resort treatment of chronic neuropathic pain. The dorsal root ganglion stimulation (DRGS) is an established therapy for patients with chronic localized neuropathic pain. The clinical success of DRGS has been published in peer-reviewed journals(4-9). However, the mechanisms of action underlying pain relief through DRG stimulation are not well understood. Therefore, we examined the effects of DRG stimulation on pain processing by recording laser evoked potentials (LEP).

 

METHODS

 

Eight patients who were diagnosed with unilateral chronic neuropathic pain on the groin or lower limb were included in the study.

LEPs were recorded from the painful dermatome (painful) and contralateral healthy dermatome (control) at time points baseline (T0) before DRGS and during DRGS at 1 month (T1) and 6 months (T2) according to the following paradigm design (fig.1)

 

•The Numerical Rating Scale (NRS) was assessed for chronic ongoing pain scores  at T0 DRGS OFF, T1 DRGS ON and T2 DRGS ON.
•During the experimental sessions, CO2 laser pulses (MCO25, KLS Martin, Germany) with a 3.5mm beam diameter and stimulus duration of 15 ms were applied. The laser power was calibrated on the control side before each session by increasing laser pulse power in steps of 1 W until clear pinprick sensation was perceived on 3 consecutive laser stimuli. In each session 40 to 50 laser pulses were applied on both the control side and the painful side.
•A 32 channel EEG system (Acti-cap, Brain Products, Germany), referenced to the nose was used to record the LEP. The data was analysed using an EEG processing software (Brain Analyzer 2.1, Brain Products, Germany). Raw EEG data was filtered (0,3-30Hz) and  sequenced (-100ms to 600ms). The epochs with eye blink or muscle artifacts were rejected by visual inspection. The N2/P2 complex was plotted from the Cz electrode, and the N2/P2 peak-to-peak amplitudes were statistically compared by using  the SPSS version 22 software (IBM, USA).
 

RESULTS

 

Case Example

 

W.S., male, 53 years old. After a microsurgical discectomy in 2004, he developed a chronic localized neuropathic pain syndrome in the upper left leg, involving the L1 and L2 dermatomes. We performed a DRG stimulation at the levels L1 and L2 on the left side (fig. 2). Baseline NRS was 7.5. Baseline LEP assessment showed a clear LEP on the control side, but no detectable LEP on the painful side. After 6 months the NRS decreased to 2 and LEP could be recorded on the painful side. (fig. 3).

 

Group data (N=8)

 

LEP N2/P2 peak-to-peak amplitude and NRS scores were compared. A non-parametric Friedman test for repeated measures revealed a significant effect of DRG stimulation on LEP peak-to-peak amplitude on the test side [χ2(2) = 12.250, p < .01] and  on NRS scores [χ2(2) = 12.800, p < .01]. LEP peak-to-peak amplitude on the control side were not significantly different across T0, T1 and T2 [χ2(2) = 3.000, p > .05]. A Wilcoxon signed-ranks test showed that LEP peak-to-peak amplitude at T0 DRGS OFF were different from T1 DRGS ON [Z = -2.521, p < .05] and T2 DRGS ON [Z = -2.521, p < .05] (fig. 4). Also, NRS scores at T0 DRGS OFF were different from T1 DRSG ON [Z = -2.527, p < .05] and T2 DRGS ON [Z = -2.527, p < .05] (fig. 5). Moreover, while there was a significant difference on N2/P2 amplitude between painful and control side at baseline, it has subsided at 1 and 6 months (fig 6).

 

CONCLUSION

 

LEP N2/P2 amplitude was restored at T1 DRGS ON and sustained till T2 DRGS ON in comparison to the baseline T0 DRGS OFF condition for painful dermatome. Chronic ongoing pain NRS score on the painful region significantly decreased at T1 DRGS ON and sustained till T2 DRGS ON in comparison to baseline T0 DRGS OFF condition. Therefore, DRG stimulation was effective in treating localized chronic neuropathic pain. Lastly, the restoration of LEP may be associated with good clinical outcome. 

References

1. Loeser JD, Treede RD. The Kyoto protocol of IASP Basic Pain Terminology. Pain. 2008;137(3):473-7. 2. van Hecke O, Austin SK, Khan RA, Smith BH, Torrance N. Neuropathic pain in the general population: a systematic review of epidemiological studies. Pain. 2014;155(4):654-62. 3.Liem L, Russo M, Huygen FJ, Van Buyten JP, Smet I, Verrills P, et al. One-Year Outcomes of Spinal Cord Stimulation of the Dorsal Root Ganglion in the Treatment of Chronic Neuropathic Pain. Neuromodulation : journal of the International Neuromodulation Society. 2014. 4. Schu S, Gulve A, Eldabe S, Baranidharan G, Wolf K, Demmel W, et al. Spinal Cord Stimulation of the Dorsal Root Ganglion for Groin Pain-A Retrospective Review. Pain practice : the official journal of World Institute of Pain. 2014 5. van Bussel CM, Stronks DL, Huygen FJ. Successful Treatment of Intractable Complex Regional Pain Syndrome Type I of the Knee With Dorsal Root Ganglion Stimulation: A Case Report. Neuromodulation : journal of the International Neuromodulation Society. 2014. 6. Van Buyten JP, Smet I, Liem L, Russo M, Huygen F. Stimulation of Dorsal Root Ganglia for the Management of Complex Regional Pain Syndrome: A Prospective Case Series. Pain practice : the official journal of World Institute of Pain. 2014. 7.Deer TR, Grigsby E, Weiner RL, Wilcosky B, Kramer JM. A prospective study of dorsal root ganglion stimulation for the relief of chronic pain. Neuromodulation : journal of the International Neuromodulation Society. 2013;16(1):67-71; discussion -2. 8. Liem L, Russo M, Huygen FJ, Van Buyten JP, Smet I, Verrills P, et al. A multicenter, prospective trial to assess the safety and performance of the spinal modulation dorsal root ganglion neurostimulator system in the treatment of chronic pain. Neuromodulation : journal of the International Neuromodulation Society. 2013;16(5):471-82; discussion 82. 9. Lynch PJ, McJunkin T, Eross E, Gooch S, Maloney J. Case report: successful epiradicular peripheral nerve stimulation of the C2 dorsal root ganglion for postherpetic neuralgia. Neuromodulation : journal of the International Neuromodulation Society. 2011;14(1):58-61; discussion.


 

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