Observing Altered Nociceptive Detection Thresholds in Patients With Persistent Spinal Pain Syndrome Type 2 With a Dorsal Root Ganglion Stimulator.

OBJECTIVES: There is a lack of clinically relevant measures for quantification of maladaptive mechanisms of the nociceptive system leading to chronic pain. Recently, we developed a method that tracks nociceptive detection thresholds (NDTs) using intraepidermal electrical stimulation. In this study, we explored the feasibility of using this NDT method in patients with persistent spinal pain syndrome type 2 (PSPS-T2) and its potential to enable observation of altered nociceptive processing induced by dorsal root ganglion (DRG) stimulation. In addition, we compared NDTs with quantitative sensory testing (QST) measurements and numeric rating scale (NRS). MATERIALS AND METHODS: A total of 12 patients with PSPS-T2 (seven men; 60.4 ± 12.3 years) experiencing chronic unilateral lower limb pain treated with DRG stimulation were included in the study. Both the NDT method and electrical and pressure QST methods were performed twice in the L5 dermatome on both the affected and the unaffected foot, once with the DRG stimulator turned off and, subsequently, once with the DRG stimulator turned on. RESULTS: The NDT method can be applied to patients with PSPS-T2. With the DRG stimulator turned off, NDTs on the affected side were significantly higher than on the unaffected side. This difference was no longer present once the DRG stimulator was turned on. Furthermore, DRG stimulation affected QST (electrical and pressure) values and NRS scores. Finally, NDTs showed larger contrasts between the sides than QST measures. CONCLUSIONS: The NDT method permitted observation of altered nociceptive function. The effect of DRG stimulation also was reflected in QST outcomes and NRS scores. The larger contrast between the sides for NDTs suggests that the NDT method might be valuable for future quantification of nociceptive dysfunction in chronic pain.

Simultaneous tracking of psychophysical detection thresholds and evoked potentials to study nociceptive processing.

Measuring altered nociceptive processing involved in chronic pain is difficult due to a lack of objective methods. Potential methods to characterize human nociceptive processing involve measuring neurophysiological activity and psychophysical responses to well-defined stimuli. To reliably measure neurophysiological activity in response to nociceptive stimulation using EEG, synchronized activation of nerve fibers and a large number of stimuli are required. On the other hand, to reliably measure psychophysical detection thresholds, selection of stimulus amplitudes around the detection threshold and many stimulus-response pairs are required. Combining the two techniques helps in quantifying the properties of nociceptive processing related to detected and non-detected stimuli around the detection threshold.The two techniques were combined in an experiment including 20 healthy participants to study the effect of intra-epidermal electrical stimulus properties (i.e. amplitude, single- or double-pulse and trial number) on the detection thresholds and vertex potentials. Generalized mixed regression and linear mixed regression were used to quantify the psychophysical detection probability and neurophysiological EEG responses, respectively.It was shown that the detection probability is significantly modulated by the stimulus amplitude, trial number, and the interaction between stimulus type and amplitude. Furthermore, EEG responses were significantly modulated by stimulus detection and trial number. Hence, we successfully demonstrated the possibility to simultaneously obtain information on psychophysical and neurophysiological properties of nociceptive processing. These results warrant further investigation of the potential of this method to observe altered nociceptive processing.