Matrix stimulation in cancer pain: Methodology, safety and effectiveness

Electrical matrix stimulation suppresses acute itch independently of activation of sleeping nociceptors

INTRODUCTION

Itch can be reduced by pain. Activation of sleeping nociceptors (CMi) is a crucial mechanism for the peripheral component of intense and long-lasting pain. Thus, activation of CMi might be especially effective in itch reduction. Electrical stimulation using sinusoidal pulses activates CMi with tolerable pain intensity, whereas short rectangular pulses with low intensity do not. In humans, histaminergic itch is mediated by histamine-sensitive CMi, whereas other pruritogens activate polymodal nociceptors (CM).

METHODS

In a psychophysical approach in a balanced crossover repeated-measures design in healthy volunteers, we activated nociceptors by two different electrical stimulation paradigms via a matrix electrode: 4 Hz sinusoidal pulses that activate C-nociceptors including CMi or 4 Hz rectangular stimuli to activate nociceptors excluding CMi. After 5-min stimulation, itch was induced by either histamine iontophoresis or application of cowhage spicules. Itch ratings were assessed via a numerical rating scale (NRS).

RESULTS

Electrical 4 Hz sine wave stimulation (0.1 mA) with low pain ratings of 1.5 (NRS; 0-10) induced an axon reflex erythema (3 cm2 ), indicating activation of CMi, whereas rectangular 0.2 ms pulses (average 0.91 mA) with the same pain rating did not. Both electrical stimulation paradigms reduced itch magnitude over time evoked by either histamine or cowhage to a similar extent. Peak maximum itch evoked by histamine was reduced by both stimulation paradigms, but not cowhage maximum itch.

DISCUSSION

Since electrical stimulation with the rectangular pulse paradigm reduces itch to a similar extent as the sine wave stimulation paradigm, the input of CMi is not necessarily required for itch suppression. The input of A-fibres and polymodal nociceptors, similarly, as also achieved by scratching, seems to be sufficient for both forms of chemically evoked itch.

SIGNIFICANCE

Since activation of CMi does not provide additional benefit for itch suppression, spinal pain pathways transmitted via CM versus CMi have differential effects on itch-processing circuits. This is important knowledge for using electrical matrix stimulation as itch suppressor since activation of sleeping nociceptors either requires significantly painful stimulation paradigms or specialized stimulation paradigms as sinusoidal pulses. An alternative approach using half-sine wave pulses with low pain intensity activating specifically polymodal nociceptors to suppress itch via matrix electrode stimulation may be considered.

Peripheral Electrical Stimulation Modulates Cortical Beta-Band Activity

Low-frequency peripheral electrical stimulation using a matrix electrode (PEMS) modulates spinal nociceptive pathways. However, the effects of this intervention on cortical oscillatory activity have not been assessed yet. The aim of this study was to investigate the effects of low-frequency PEMS (4 Hz) on cortical oscillatory activity in different brain states in healthy pain-free participants. In experiment 1, PEMS was compared to sham stimulation. In experiment 2, motor imagery (MI) was used to modulate the sensorimotor brain state. PEMS was applied either during MI-induced oscillatory desynchronization (concurrent PEMS) or after MI (delayed PEMS) in a cross-over design. For both experiments, PEMS was applied on the left forearm and resting-state electroencephalography (EEG) was recording before and after each stimulation condition. Experiment 1 showed a significant decrease of global resting-state beta power after PEMS compared to sham (p = 0.016), with a median change from baseline of −16% for PEMS and −0.54% for sham. A cluster-based permutation test showed a significant difference in resting-state beta power comparing pre- and post-PEMS (p = 0.018) that was most pronounced over bilateral central and left frontal sensors. Experiment 2 did not identify a significant difference in the change from baseline of global EEG power for concurrent PEMS compared to delayed PEMS. Two cluster-based permutation tests suggested that frontal beta power may be increased following both concurrent and delayed PEMS. This study provides novel evidence for supraspinal effects of low-frequency PEMS and an initial indication that the presence of a cognitive task such as MI may influence the effects of PEMS on beta activity. Chronic pain has been associated with changes in beta activity, in particular an increase of beta power in frontal regions. Thus, brain state-dependent PEMS may offer a novel approach to the treatment of chronic pain. However, further studies are warranted to investigate optimal stimulation conditions to achieve a reduction of pain.

Transcutaneous electrical nerve stimulation for advanced cancer pain inpatients in specialist palliative care-a blinded, randomized, sham-controlled pilot cross-over trial

PURPOSE

Transcutaneous electrical nerve stimulation (TENS) is a treatment option for cancer pain, but the evidence is inconclusive. We aimed to evaluate the efficacy and safety of TENS.

METHODS

A blinded, randomized, sham-controlled pilot cross-over trial (NCT02655289) was conducted on an inpatient specialist palliative care ward. We included adult inpatients with cancer pain ≥ 3 on an 11-point numerical rating scale (NRS). Intensity-modulated high TENS (IMT) was compared with placebo TENS (PBT). Patients used both modes according to their preferred application scheme during 24 h with a 24-h washout phase. The primary outcome was change in average pain intensity on the NRS during the preceding 24 h. Responders were patients with at least a "slight improvement."

RESULTS

Of 632 patients screened, 25 were randomized (sequence IMT-PBT = 13 and PBT-IMT = 12). Finally, 11 patients in IMT-PBT and 9 in PBT-IMT completed the study (N = 20). The primary outcome did not differ between groups (IMT minus PBT: - 0.2, 95% confidence interval - 0.9 to 0.6). However, responder rates were higher in IMT (17/20 [85%] vs. 10/20 [50%], p = 0.0428). Two patients experienced an uncomfortable feeling caused by the current, one after IMT and one after PBT. Seven patients (35%) desired a TENS prescription. Women and patients with incident pain were most likely to benefit from TENS.

CONCLUSION

TENS was safe, but IMT was unlikely to offer more analgesic effects than PBT. Even though many patients desired a TENS prescription, 50% still reported at least "slight pain relief" from PBT. Differences for gender and incident pain aspects demand future trials.

Matrix stimulation in chronic pruritus: A randomized controlled study

Chronic pruritus is one of the main symptoms in dermatology. We investigated a new intervention for chronic pruritus by neurostimulation through matrix electrodes. In this randomized controlled trial, 29 patients with chronic pruritus caused by a variety of dermatological diseases were allocated to an experimental group (EG; n = 14, 4-Hz neurostimulation of the itching area through matrix electrodes) or the control group (CG; n = 15, placement of matrix electrodes without neurostimulation). Outcome measures were the itching sensation as measured by a Numerical Rating Scale immediately after the intervention and the intermediate effect measured by the average itching sensation on the day before the intervention compared with the average itching sensation on day 1, 2 and 3 after the intervention. Regarding the short-term effect on itching, the anova showed a significant interaction effect for the 5-min stimulation with a larger reduction in the EG with a large effect size of d = 1.10. The average reduction in itching intensity was 78.2% for the EG compared with 34.3% for the CG. For the intermediate effect, no significant interaction was found (F = 1.721, P = 0.199). Comparing the itching sensation at day 0 with day 3, the interaction effect showed a statistical trend toward a greater reduction in the EG (F = 3.178, P = 0.086; statistical trend, d = 0.69). This study proved that neurostimulation through matrix electrodes is effective in the short-term reduction of itching in patients with chronic pruritus caused by dermatological diseases. Additional studies are needed with larger patient pools and covering longer study periods.