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
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).
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)
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).
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.
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