Comparison of the analgesic effects of "superficial" and "deep" repetitive transcranial magnetic stimulation in patients with central neuropathic pain: a randomized sham-controlled multicenter international crossover study.

ABSTRACT: We directly compared the analgesic effects of "superficial" and 'deep" repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex in patients with central neuropathic pain. Fifty-nine consecutive patients were randomly assigned to active or sham "superficial" (using a figure-of-8 [F8]-coil) or "deep" (using a Hesed [H]-coil) stimulation according to a double-blind crossover design. Each treatment period consisted of 5 daily stimulation sessions and 2 follow-up visits at 1 and 3 weeks after the last stimulation session. The primary outcome was the comparison of the mean change in average pain intensity over the course of the treatment (group × time interaction). Secondary outcomes included neuropathic symptoms (NPSI), pain interference, patient global impression of change (PGIC), anxiety, depression, and catastrophizing. In total, 51 patients participated in at least one session of both treatments. There was a significant interaction between "treatment" and "time" (F = 2.7; P = 0.0024), indicating that both figure-8 (F8-coil) and H-coil active stimulation induced significantly higher analgesic effects than sham stimulation. The analgesic effects of both types of coils had a similar magnitude but were only moderately correlated ( r = 0.39, P = 0.02). The effects of F8-coil stimulation appeared earlier, whereas the effects of H-coil stimulation were delayed, but tended to last longer (up to 3 weeks) as regards to several secondary outcomes (PGIC and total NPSI score). In conclusion, "deep" and "superficial" rTMS induced analgesic effects of similar magnitude in patients with central pain, which may involve different mechanisms of action.

Small nerve fiber selectivity of laser and intraepidermal electrical stimulation: A comparative study between glabrous and hairy skin.

OBJECTIVES: In clinical neurophysiology practice, various methods of stimulation can be used to activate small-diameter nociceptive cutaneous afferents located in the epidermis. These methods include different types of laser and intraepidermal electrical stimulation techniques. The diffusion of the stimulation in the skin, inside or under the epidermis, depends on laser wavelength and electrode design, in particular. The aim of this study was to compare several of these techniques in their ability to selectively stimulate small nerve fibers. METHODS: In 8 healthy subjects, laser stimulation (using a CO2 or Nd:YAP laser) and intraepidermal electrical stimulation (using a micropatterned, concentric planar, or concentric needle electrode), were applied at increasing energy or intensity on the dorsal or volar aspect of the right hand or foot. The subjects were asked to define the perceived sensation (warm, pinprick, or electric shock sensation, corresponding to the activation of C fibers, Aδ fibers, or Aß fibers, respectively) after each stimulation. Depending on the difference in the sensations perceived between dorsal (hairy skin with thin stratum corneum) and volar (glabrous skin with thick stratum corneum) stimulations, the diffusion of the stimulation inside or under the epidermis and the nature of the activated afferents were determined. RESULTS: Regarding laser stimulation, the perceived sensations turned from warm to pinprick with increasing energies of stimulation, in particular with the Nd:YAP laser, of which pulse could penetrate deep in the skin according to its short wavelength. In contrast, CO2 laser stimulation produced only warm sensations and no pricking sensation when applied to the glabrous skin, perhaps due to a thicker stratum corneum and the shallow penetration of the CO2 laser pulse. Regarding intraepidermal electrical stimulation using concentric electrodes, the perceived sensations turned from pinprick to a combination of pinprick and electrical shocks with increasing intensities. Using the concentric planar electrode, the sensations perceived at high stimulation intensity even consisted of electric shocks without concomitant pinprick. In contrast, using the micropatterned electrode, only pinprick sensations were produced by the stimulation of the hairy skin, while the stimulation of the glabrous skin produced no sensation at all within the limits of stimulation intensities used in this study. CONCLUSIONS: Using the CO2 laser or the micropatterned electrode, pinprick sensations were selectively produced by the stimulation of hairy skin, while only warm sensation or no sensation at all were produced by the stimulation of glabrous skin. These two techniques appear to be more selective with a limited diffusion of the stimulation into the skin, restricting the activation of sensory afferents to the most superficial and smallest intraepidermal nerve fibers.

Relieving peripheral neuropathic pain by increasing the power-ratio of low-ß over high-ß activities in the central cortical region with EEG-based neurofeedback: Study protocol for a controlled pilot trial (SMRPain study).

BACKGROUND: Chronic neuropathic pain associated with peripheral neuropathies cannot be attributed solely to lesions of peripheral sensory axons and likely involves alteration in the processing of nociceptive information in the central nervous system in most patients. Few data are available regarding EEG correlates of chronic neuropathic pain. The fact is that effective cortical neuromodulation strategies to treat neuropathic pain target the precentral cortical region, i.e. a cortical area corresponding to the motor cortex. It is not known how these strategies might modulate brain rhythms in the central cortical region, but it can be speculated that sensorimotor rhythms (SMRs) are modified. Another potent way of modulating cortical rhythms is to use EEG-based neurofeedback (NFB). Rare studies previously aimed at relieving neuropathic pain using EEG-NFB training. METHODS/DESIGN: The objective of this single-centre, single-blinded, randomized controlled pilot study is to assess the value of an EEG-NFB procedure to relieve chronic neuropathic pain in patients with painful peripheral neuropathy. A series of 32 patients will be randomly assigned to one of the two following EEG-NFB protocols, aimed at increasing either the low-ß(SMR)/high-ß ratio (n=16) or the α(µ)/θ ratio (n=16) at central (rolandic) cortical level. Various clinical outcome measures will be collected before and one week after 12 EEG-NFB sessions performed over 4weeks. Resting-state EEG will also be recorded immediately before and after each NFB session. The primary endpoint will be the change in the impact of pain on patient's daily functioning, as assessed on the Interference Scale of the short form of the Brief Pain Inventory. DISCUSSION: The value of EEG-NFB procedures to relieve neuropathic pain has been rarely studied. This pilot study will attempt to show the value of endogenous modulation of brain rhythms in the central (rolandic) region in the frequency band corresponding to the frequency of stimulation currently used by therapeutic motor cortex stimulation. In the case of significant clinical benefit produced by the low-ß(SMR)/high-ß ratio increasing strategy, this work could pave the way for using EEG-NFB training within the armamentarium of neuropathic pain therapy.