A Novel Method of Eliciting Pain-Related Potentials by Transcutaneous Electrical Stimulation

Posttraumatic headache: pain related evoked potentials (PREP) and conditioned pain modulation (CPM) to assess the pain modulatory function

Posttraumatic headache (PTH) is common following traumatic brain injury and impacts quality of life. We investigated descending pain modulation as one possible mechanism for PTH and correlated it to clinical measures. Pain-related evoked potentials (PREP) were recorded in 26 PTH-patients and 20 controls after electrical stimulation at the right hand and forehead with concentric surface electrodes. Conditioned pain modulation (CPM) was assessed using painful cutaneous electric stimulation (PCES) on the right hand as test stimulus and immersion of the left hand into 10 °C-cold water bath as conditioning stimulus based on changes in pain intensity and in amplitudes of PCES-evoked potentials. All participants completed questionnaires assessing depression, anxiety, and pain catastrophising. PTH-patients reported significantly higher pain ratings during PREP-recording in both areas despite similar stimulus intensity at pain threshold. N1P1-amplitudes during PREP and CPM-assessment were lower in patients in both areas, but statistically significant only on the hand. Both, PREP-N1-latencies and CPM-effects (based on the N1P1-amplitudes and pain ratings) were similar in both groups. Patients showed significantly higher ratings for anxiety and depression, which did not correlate with the CPM-effect. Our results indicate generalized hyperalgesia for electrical stimuli in both hand and face in PTH. The lacking correlation between pain ratings and EEG parameters indicates different mechanisms of pain perception and nociception.

Multiple averaged records to identify Aδ-fibers in sensory nerves

BACKGROUND

Existing methods identify only ≈10 Aδ-fibers in human sensory nerves per recording. This study examines methods to increase the detection of Aδ-fibers.

NEW METHOD

Two to 20 averages of 500 replicate responses to epidermal nerve stimulation are obtained. Pairs of different averages are constructed. Each pair is analyzed with algorithms applied to amplitude and frequency to detect replication of responses to stimulation as "simultaneous similarities in two averages" (SS2AVs) at ≥99.5th percentile of control. In a pair of averages the latencies of amplitude and frequency SS2AVs for the same response to stimulation may differ by ≤0.25 ms. Therefore, Aδ-fibers are identified by the 0.25 ms moving sum of SS2AV latencies of the pairs of averages.

RESULTS

Increasing averages increases pairs of different averages and detection of Aδ-fibers: from 2 to 10 Aδ-fibers with two averages (one pair) to >50 Aδ-fibers with 12-20 averages (66-190 pairs).

COMPARISON WITH EXISTING METHOD(S)

Existing methods identify ≤10 Aδ-fibers in 10 averages/45 pairs with the medians of amplitude and frequency algorithms applied to all 45 pairs. This study identifies Aδ-fibers (i) by applying these algorithms at the 99.5th percentile of control, (ii) to each pair of averages and (iii) by the 0.25 ms sum of algorithm identified events (SS2AVs) in all pairs. These three changes significantly increase the detection of Aδ-fibers, e.g., in 10 averages/45pairs from 10 to 45.

CONCLUSIONS

Three modifications of existing methods can increase the detection of Aδ-fibers to an amount suitable (>50 with ≥12 averages) for statistical comparison of different nerves.

Distinguishing fibromyalgia syndrome from small fiber neuropathy: a clinical guide

Introduction

Fibromyalgia syndrome (FMS) and small fiber neuropathy (SFN) are distinct pain conditions that share commonalities and may be challenging as for differential diagnosis.

Objective

To comprehensively investigate clinical characteristics of women with FMS and SFN to determine clinically applicable parameters for differentiation.

Methods

We retrospectively analyzed medical records of 158 women with FMS and 53 with SFN focusing on pain-specific medical and family history, accompanying symptoms, additional diseases, and treatment. We investigated data obtained using standardized pain, depression, and anxiety questionnaires. We further analyzed test results and findings obtained in standardized small fiber tests.

Results

FMS patients were on average ten years younger at symptom onset, described higher pain intensities requiring frequent change of pharmaceutics, and reported generalized pain compared to SFN. Pain in FMS was accompanied by irritable bowel or sleep disturbances, and in SFN by paresthesias, numbness, and impaired glucose metabolism (P < 0.01 each). Family history was informative for chronic pain and affective disorders in FMS (P < 0.001) and for neurological disorders in SFN patients (P < 0.001). Small fiber pathology in terms of skin denervation and/or thermal sensory threshold elevation was present in 110/158 (69.7 %) FMS patients and 39/53 (73.6 %) SFN patients. FMS patients mainly showed proximally reduced skin innervation and higher corneal nerve branch densities (p<0.001) whereas SFN patients were characterized by reduced cold detection and prolonged electrical A-delta conduction latencies (P < 0.05).

Conclusions

Our data show that FMS and SFN differ substantially. Detailed pain, drug and family history, investigating blood glucose metabolism, and applying differential small fiber tests may help to improve diagnostic differentiation and targeted therapy.

Anodal transcutaneous spinal direct current stimulation influences the amplitude of pain-related evoked potentials in healthy subjects

It has already been described that transcutaneous spinal direct current stimulation (tsDCS) can selectively influence nociceptive evoked potentials. This study is the first aiming to prove an influence of tsDCS on pain-related evoked potentials (PREP) using concentric surface electrodes (CE), whose nociceptive specificity is still under discussion. 28 healthy subjects participated in this sham-controlled, double-blind cross-over study. All subjects underwent one session of anodal and one session of sham low-thoracic tsDCS. Before and after the intervention, PREP using CE, PREP-induced pain perception and somatosensory evoked potentials (SEP) were assessed on the right upper and lower limb. We found a decrease in PREP amplitude at the lower limb after sham stimulation, but not after anodal tsDCS, while SEP remained unchanged under all studied conditions. There was no difference between the effects of anodal tsDCS and sham stimulation on the studied parameters assessed at the upper limb. PREP-induced pain of the upper and lower limb increased after anodal tsDCS. The ability of influencing PREP using a CE at the spinal level in contrast to SEP suggests that PREP using CE follows the spinothalamic pathway and supports the assumption that it is specifically nociceptive. However, while mainly inhibitory effects on nociceptive stimuli have already been described, our results rather suggest that anodal tsDCS has a sensitizing effect. This may indicate that the mechanisms underlying the elicitation of PREP with CE are not the same as for the other nociceptive evoked potentials. The effects on the processing of different types of painful stimuli should be directly compared in future studies.

Pain-Related Vertex Evoked Potentials. Comparison of Surface Electrical to Heat Stimulation

INTRODUCTION

Demonstration of nociceptive fiber abnormality is important for diagnosing neuropathic pain and small fiber neuropathies. This is usually assessed by brief heat pulses using lasers, contact heat, or special electrodes. We hypothesized that pain-related evoked potentials to conventional surface electrical stimulation (PREPse) can index Aδ afferences despite tactile Aß fibers coactivation. PREPse may be more readily used clinically than contact heat evoked potentials (CHEPS).

METHODS

Twenty-eight healthy subjects. Vertex (Cz-A1/A2) recordings. Electrical stimulation of middle finger and second toe with conventional ring, and forearm/leg skin with cup, electrodes. Contact heat stimulation to forearm and leg. Compression ischemic nerve blockade.

RESULTS

PREPse peripheral velocities were within the midrange of Aδ fibers. N1-P1 amplitude increased with pain numerical rating scale graded (0-10) electrical stimulation (n = 25) and decreased with increasing stimulation frequency. Amplitudes were unchanged by different presentation orders of four stimulation intensities. PREPse N1 (∼130 milliseconds) and N2 (∼345 milliseconds) peaks were approximately 40 milliseconds earlier than that with CHEPS. PREPse and CHEPS N1-N2 interpeak latency (∼207 milliseconds) were similar. PREPse became unrecordable with nerve blockade of Aδ fibers.

CONCLUSIONS

PREPse earlier N1 and N2 peaks, and similar interpeak N1-N2 latencies and central conduction velocities, or synaptic delays, to CHEPS are consistent with direct stimulation of Aδ fibers. The relation of vertex PREPse amplitude and pain, or the differential effects of frequency stimulation, is similar to pain-related evoked potential to laser, special electrodes, or contact heat stimulation. The relationship to Aδ was validated by conduction velocity and nerve block. Clinical utility of PREPse compared with CHEPS needs validation in somatosensory pathways lesions.

Pain-related evoked potentials with concentric surface electrodes in patients and healthy subjects: a systematic review

Pain-related evoked potentials with concentric surface electrodes (PREP with CE) have been increasingly used in the diagnostics of polyneuropathies as well as in pain research. However, the study results are partly inconsistent regarding their utility to distinguish between normal and abnormal findings. The present systematic review aimed to summarise and compare study results, where PREP with CE were used in healthy subjects or patients and to identify possible influencing factors. We found 36 research articles, of which 21 investigated disorders in patients compared to healthy controls, while the other 15 focussed on basic research in healthy subjects. Patients with polyneuropathies showed the most consistent PREP results with similar prolonged latencies and reduced amplitude values. Findings in other patient groups or in healthy subjects were more heterogeneous. There was evidence for an influence by age and height as well as by central effects like emotions, which should be considered in further studies. Further systematic research analysing PREP results depending on individual and disease-specific factors is needed to develop optimal normative values.

Peripheral Neuropathy in Systemic Autoimmune Rheumatic Diseases-Diagnosis and Treatment

Peripheral neuropathy (PN) is frequently observed in systemic rheumatic diseases and is a challenge in clinical practice. We aimed to review the evidence on the subject and proposed a comprehensive approach to these patients, facilitating diagnosis and management. We searched the MEDLINE database for the terms (and its respective Medical Subject Headings (MeSH) terms): "peripheral neuropathy" AND "rheumatic diseases" OR "systemic lupus erythematosus", "rheumatoid arthritis", "Sjogren syndrome", and "vasculitis" from 2000 to 2023. This literature review focuses on the diagnostic workup of PNs related to systemic lupus erythematosus, Sjögren's syndrome, rheumatoid arthritis, and systemic vasculitis. For every type of PN, we provide a pragmatic flowchart for diagnosis and also describe evidence-based strategies of treatment.

Acupuncture-Induced Changes in Nociception, Measured by Pain-Related Evoked Potentials: A Pilot Mechanistic Study

Objective: The nociceptive system has been implicated in acupuncture analgesia, although acupuncture's precise mechanism of action remains unknown. Electric pain-related evoked potentials (PREPs) have emerged as an effective and reliable electrophysiologic method for evaluation of the human nociceptive system by electric stimulation of nociceptive Aδ and C fibers. This pilot mechanistic study aims to assess the feasibility of using advanced PREP techniques together with electroacupuncture and to use PREPs to characterize acupuncture's effect on nociception. Methods: Seven healthy volunteers underwent a previously designed electroacupuncture protocol using acupoints in the legs bilaterally, which has been demonstrated to induce systemic analgesia. Advanced PREP techniques involving tripolar stimulating electrode, varying interstimulus interval, and incorporating a cognitive task during PREPs were used. PREPs were assessed before electroacupuncture, during electroacupuncture, and 30 min after electroacupuncture. Subjective pain perception in response to the PREP-related electric pain stimuli delivered to the nondominant hand was assessed on the visual analog scale (VAS) at baseline, during electroacupuncture, and 30 min postelectroacupuncture. Results: Reliable PREP N1, P1, and N2 waves were obtained from all subjects at the following average latencies: N1 = 131.5 msec, P1 = 189.4 msec, and N2 = 231.1 msec. Electroacupuncture caused a significant reduction in PREP N1P1 wave amplitudes from 25.6 to 15.4 μV (p = 0.006) and electric pain perception on the VAS-from 2.86 to 2.14 (p = 0.008), compared to baseline. These effects were sustained at 30 min postacupuncture with N1P1 wave amplitude 17.2 μV (p = 0.030) and VAS 2.28 (p = 0.030), compared to baseline. Conclusions: Electroacupuncture causes significant changes in objective nociception, measured by PREP N1P1 wave amplitudes, and in subjective nociception, measured by the VAS, and these effects are sustained for 30 min after electroacupuncture. Planned future studies will involve chronic pain populations and will aim to assess acupuncture's longer term analgesic effects.

The influence of EEG oscillations, heart rate variability changes, and personality on self-pain and empathy for pain under placebo analgesia

We induced placebo analgesia (PA), a phenomenon explicitly attenuating the self-pain feeling, to assess whether this resulted in reduced empathy pain when witnessing a confederate undergoing such pain experience. We recorded EEG and electrocardiogram during a painful Control and PA treatment in healthy adults who rated their experienced pain and empathy for pain. We derived HRV changes and, using wavelet analysis of non-phase-locked event-related EEG oscillations, EEG spectral power differences for self-pain and other-pain conditions. First-hand PA reduced self-pain and self-unpleasantness, whereas we observed only a slight decrease in other unpleasantness. We derived linear combinations of HRV and EEG band power changes significantly associated with self-pain and empathy for pain changes using PCAs. Lower Behavioral Inhibition System scores predicted self-pain reduction through the mediating effect of a relative HR-slowing and a decreased midline ϑ-band (4-8 Hz) power factor moderated by lower Fight-Flight-Freeze System trait scores. In the other-pain condition, we detected a direct positive influence of Total Empathic Ability on the other-pain decline with a mediating role of the midline β2-band (22-30 Hz) power reduction. These findings suggest that PA modulation of first-hand versus other pain relies on functionally different physiological processes involving different personality traits.

Workshops of the Eighth International Brain-Computer Interface Meeting: BCIs: The Next Frontier

The Eighth International Brain-Computer Interface (BCI) Meeting was held June 7-9th, 2021 in a virtual format. The conference continued the BCI Meeting series' interactive nature with 21 workshops covering topics in BCI (also called brain-machine interface) research. As in the past, workshops covered the breadth of topics in BCI. Some workshops provided detailed examinations of specific methods, hardware, or processes. Others focused on specific BCI applications or user groups. Several workshops continued consensus building efforts designed to create BCI standards and increase the ease of comparisons between studies and the potential for meta-analysis and large multi-site clinical trials. Ethical and translational considerations were both the primary topic for some workshops or an important secondary consideration for others. The range of BCI applications continues to expand, with more workshops focusing on approaches that can extend beyond the needs of those with physical impairments. This paper summarizes each workshop, provides background information and references for further study, presents an overview of the discussion topics, and describes the conclusion, challenges, or initiatives that resulted from the interactions and discussion at the workshop.

Novel surface electrode design for preferential activation of cutaneous nociceptors

Objective Small area electrodes enable preferential activation of nociceptive fibers. It is debated, however, whether co-activation of large fibers still occurs for the existing electrode designs. Moreover, existing electrodes are limited to low stimulation intensities, for which behavioral and physiological responses may be considered less reliable. A recent optimization study showed that there is a potential for improving electrode performance and increase the range of possible stimulation intensities. Based on those results, the present study introduces and tests a novel planar concentric array electrode design for small fiber activation in healthy volunteers. Approach Volunteers received electrical stimulation with the planar concentric array electrode and a regular patch electrode. Perception thresholds were estimated at the beginning and the end of the experiment. Evoked cortical potentials were recorded in blocks of 30 stimuli. For the patch, stimulation intensity was set to two times perception threshold (PT), while three intensities, 2, 5, and 10 times PT, were applied with the planar concentric array electrode. Sensation quality, numerical-rating scores, and reaction times were obtained for each PT estimation and during each block of evoked potential recordings. Main results Stimulation with the patch electrode was characterized as dull, while stimulation with the planar concentric array electrode was characterized as sharp, with increased sharpness for increasing stimulus intensity. Likewise, NRS scores were higher for the planar concentric array electrode compared to the patch and increased with increasing stimulation intensity. Reaction times and ERP latencies were longer for the planar concentric array electrode compared to the patch. Significance The presented novel planar concentric array electrode is a small, non-invasive, and single-use electrode that has the potential to investigate small fiber neuropathy and pain mechanisms, as it is small fiber preferential for a wide range of stimulation intensities.

Median amplitude and frequency analysis of sensory nerve responses to intraepidermal stimulation

BACKGROUND

In clinical practice, small myelinated sensory fibers conveying pain and other sensations, Aδ-fibers, cannot be examined with available nerve conduction study techniques.

NEW METHOD

Equipment available in clinical neurophysiology laboratories is used to record from human sensory nerves multiple averaged responses to non-painful stimulation of intraepidermal nerves. Ten averaged responses are analyzed in all possible pair combinations with an algorithm applied to a 0.45 ms period of amplitude and frequency (power spectrum). The median of the algorithms is compared to control data to identify potentials generated as response to intraepidermal stimulation.

RESULTS

Median analysis of the algorithm applied to amplitude and frequency of multiple record pairs identifies potentials with conduction velocities of Aδ-fibers. The analysis of frequency (power spectrum) adds data to the analysis of amplitude. Median analysis of multiple record pairs yields more data than analysis of one pair of alternate averages with the same algorithms.

COMPARISON WITH EXISTING METHOD(S)

At present, analysis of one pair of alternate average records with an algorithm is the only method to identify Aδ-fiber generated potentials. Median analysis of the same algorithm applied to the amplitude of multiple record pairs increases the number of Aδ-fiber generated potentials identified. Neither median analysis of amplitude nor frequency of multiple records pairs has ever been used for conduction studies of nerve fibers, including Aδ-fibers.

CONCLUSIONS

Stimulation, recording and data analysis methods used in this study can be applied in the clinical EMG laboratory to identify the conduction velocities of Aδ-fibers in human sensory nerves.

Intra-epidermal evoked potentials: A promising tool for spinal disorders?

OBJECTIVES

To test the robustness and signal-to-noise ratio of pain-related evoked potentials following intra-epidermal electrical stimulation (IES) compared to contact heat stimulation in healthy controls, and to explore the feasibility and potential added value of IES in the diagnosis of spinal disorders.

METHODS

Pain-related evoked potentials induced by IES (custom-made, non-invasive, concentric triple pin electrode with steel pins protruding 1 mm from the anode, triangularly separated by 7-10 mm respectively) and contact heat stimulation were compared in 30 healthy subjects. Stimuli were applied to four different body sites. Two IES intensities, i.e., high (individually adapted to contact heat painfulness) and low (1.5 times pain threshold), were used. Additionally, a 40-year-old patient with unilateral dissociated sensory loss due to a multi-segmental syringohydromyelia was assessed comparing IES and contact heat stimulation.

RESULTS

Both IES and contact heat stimulation led to robust pain-related evoked potentials recorded in all healthy subjects. Low intensity IES evoked potentials (14.1-38.0 µV) had similar amplitudes as contact heat evoked potentials (11.8-32.3 µV), while pain ratings on the numeric rating scale were lower for IES (0.8-2.5, compared to 1.5-3.9 for contact heat stimulation). High intensity IES led to evoked potentials with higher signal-to-noise ratio than low intensity IES and contact heat stimulation. The patient case showed impaired pain-related evoked potentials in segments with hypoalgesia for both IES modes. IES evoked potentials were preserved, with delayed latencies, while contact heat evoked potentials were abolished.

CONCLUSION

IES evoked robust pain-related cortical potentials, while being less painful in healthy controls. The improved signal-to-noise ratio supports the use of IES for objective segmental testing of nociceptive processing. This was highlighted in a spinal syndrome case, where IES as well as contact heat stimulation reliably detected impaired segmental nociception.

Give me a pain that I am used to: distinct habituation patterns to painful and non-painful stimulation

Pain habituation is associated with a decrease of activation in brain areas related to pain perception. However, little is known about the specificity of these decreases to pain, as habituation has also been described for other responses like spinal reflexes and other sensory responses. Thus, it might be hypothesized that previously reported reductions in activation are not specifically related to pain habituation. For this reason, we performed a 3 T fMRI study using either painful or non-painful electrical stimulation via an electrode attached to the back of the left hand. Contrasting painful vs. non-painful stimulation revealed significant activation clusters in regions well-known to be related to pain processing, such as bilateral anterior and posterior insula, primary/secondary sensory cortices (S1/S2) and anterior midcingulate cortex (aMCC). Importantly, our results show distinct habituation patterns for painful (in aMCC) and non-painful (contralateral claustrum) stimulation, while similar habituation for both types of stimulation was identified in bilateral inferior frontal gyrus (IFG) and contralateral S2. Our findings thus distinguish a general habituation in somatosensory processing (S2) and reduced attention (IFG) from specific pain and non-pain related habituation effects where pain-specific habituation effects within the aMCC highlight a change in affective pain perception.

Measuring Latency Variations in Evoked Potential Components Using a Simple Autocorrelation Technique

Interpretation of averaged evoked potentials is difficult when the time relationship between stimulus and response is not constant. Later components are more prone to latency jitter, making them insufficiently reliable for routine clinical use even though they could contribute to greater understanding of the functioning of polysynaptic components of the afferent nervous system. This study is aimed at providing a simple but effective method of identifying and quantifying latency jitter in averaged evoked potentials. Autocorrelation techniques were applied within defined time windows on simulated jittered signals embedded within the noise component of recorded evoked potentials and on real examples of somatosensory evoked potentials. We demonstrated that the technique accurately identifies the distribution and maximum levels of jitter of the simulated components and clearly identifies the jitter properties of real evoked potential recording components. This method is designed to complement the conventional analytical methods used in neurophysiological practice to provide valuable additional information about the distribution of latency jitter within an averaged evoked potential. It will be useful for the assessment of the reliability of averaged components and will aid the interpretation of longer-latency, polysynaptic components such as those found in nociceptive evoked potentials.

Evozierte Potenziale – Reminder und Update

Mit Hilfe der evozierten Potenziale und der magnetisch evozierten motorischen Potenziale können verlängerte Latenzen zentraler Leitungsbahnen und peripherer Nerven nachgewiesen oder ausgeschlossen werden. Somit können Symptome objektiviert und quantifiziert sowie Läsionen lokalisiert werden. In diesem Beitrag werden Durchführung und Indikationen der einzelnen Modalitäten zusammengefasst und Neuerungen berichtet.

ERP Indicators of Self-Pain and Other Pain Reductions due to Placebo Analgesia Responding: The Moderating Role of the Fight-Flight-Freeze System

This study evaluates the modulation of phasic pain and empathy for pain induced by placebo analgesia during pain and empathy for pain tasks. Because pain can be conceptualized as a dangerous stimulus that generates avoidance, we evaluated how approach and avoidance personality traits modulate pain and empathy for pain responses. We induced placebo analgesia to test whether this also reduces self-pain and other pain. Amplitude measures of the N1, P2, and P3 ERPs components, elicited by electric stimulations, were obtained during a painful control, as well as during a placebo treatment expected to induce placebo analgesia. The placebo treatment produced a reduction in pain and unpleasantness perceived, whereas we observed a decrease in the empathy unpleasantness alone during the empathy pain condition. The moderator effects of the fight-flight-freeze system (FFFS) in the relationships linking P2 and P3 amplitude changes with pain reduction were both significant among low to moderate FFFS values. These observations are consistent with the idea that lower FFFS (active avoidance) scores can predict placebo-induced pain reduction. Finally, in line with the revised Reinforcement Sensitivity Theory (r-RST), we can assume that phasic pain is an aversive stimulus activating the active-avoidance behavior to bring the system back to homeostasis.

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 Aβ 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.

Early nociceptive evoked potentials (NEPs) recorded from the scalp

OBJECTIVE

Neurophysiological investigation of nociceptive pathway has so far been limited to late cortical responses. We sought to detect early components of the cortical evoked potentials possibly reflecting primary sensory activity.

METHODS

The 150 IDE micropatterned electrode was used to selectively activate Aδ intraepidermic fibres of the right hand dorsum in 25 healthy subjects and 3 patients suffering from trigeminal neuralgia. Neurographic recordings were performed to assess type of stimulated fibres and check selectivity. Cortical evoked potentials were recorded from C3'-Fz and Cz-Au1.

RESULTS

Neurographic recordings confirmed selective activation of Aδ fibres. Early components were detected after repetitive stimulation (0.83/s rate and 250-500 averages); the first negative component occured at 40 ms (N40) on the contralateral scalp.

CONCLUSIONS

The provided data support the hypothesis that N40 could be the cortical primary response conducted by fast Aδ fibres.

SIGNIFICANCE

This is the first report of early, possibly primary, cortical responses in humans by nociceptive peripheral stimulation. Although not perfected yet to allow widespread diagnostic use, this is probably the only method to allow fully objective evaluation of the nociceptive system, with important future implications in experimental and clinical neurophysiology.

Slowly conducting potentials in human sensory nerves

BACKGROUND

In clinical practice, small myelinated sensory fibers, Aδ-fibers, conveying mainly pain and temperature sensations, cannot be examined with available nerve conduction study techniques. Currently, these fibers can only be examined with experimental or very specialized and not commonly available nerve conduction techniques, or only indirectly with cerebral evoked potentials.

NEW METHOD

This study uses equipment and methods available in clinical neurophysiology laboratories to record from human sensory nerves ≥1000 averaged responses to focal, non-painful stimuli applied by a special electrode to epidermal nerves. The averaged responses to odd numbered stimuli are compared to the averaged responses to even numbered stimuli. An algorithm identifies potentials common in both averages. The 99^th and 99.9^th percentiles for this algorithm are obtained from control records without stimulation and applied to records with stimulation to identify potentials resulting from stimulation of intraepidermal nerves.

RESULTS

The algorithm identifies numerous negative and positive potentials as being different from controls at the 99th and 99.9^th percentile levels. The conduction velocities of the potentials range from of 1.3-29.9 m/s and are compatible with conduction velocities of Aδ-fibers.

COMPARISON WITH EXISTING METHOD(S)

No existing methods.

CONCLUSIONS

The stimulation, recording and data analysis methods used in this study can be applied in the clinical EMG laboratory to identify Aδ-fibers in human sensory nerves.

Increased preferential activation of small cutaneous nerve fibers by optimization of electrode design parameters

OBJECTIVE

Electrical preferential activation of small nociceptive fibers may be achieved with the use of specialized small area electrodes, however, the existing electrodes are limited to low stimulation intensities. As existing electrodes have been developed empirically, the present study aimed to use computational modeling and optimization techniques to investigate if changes in electrode design parameters could improve the preferential activation of small fibers.

APPROACH

Two finite element models; one of a planar concentric and one of an intra-epidermal electrode were combined with two multi-compartmental nerve fiber models of an Aδ-fiber and an Aβ-fiber. These two-step hybrid models were used for the optimization of four electrode parameters; anode area, anode-cathode distance, cathode area, and cathode protrusion. Optimization was performed using a gradient-free bounded Nelder-Mead algorithm, to maximize the current activation threshold ratio between the Aβ-fiber model and the Aδ-fiber model.

MAIN RESULTS

All electrode parameters were optimal at their lower bound, except the cathode protrusion, which was optimal a few micrometers above the location of the Aδ-fiber model. A small cathode area is essential for producing a high current density in the epidermal skin layer enabling activation of small fibers, while a small anode area and anode-cathode distance are important for the minimization of the current spread to deeper tissues, making it less likely to activate large fibers. Combining each of the optimized electrode parameters improved the preferential activation of small fibers in comparison to existing electrodes, by increasing the activation threshold ratio between the two nerve fiber types. The maximum increase in the activation threshold ratio was 289% and 595% for the intra-epidermal and planar concentric design, respectively.

SIGNIFICANCE

The present study showed that electrical preferential small fiber activation can be improved by electrode design. Additionally, the results may be used for the production of an electrode that could potentially be used for clinical assessment of small fiber neuropathy.

Distraction by a cognitive task has a higher impact on electrophysiological measures compared with conditioned pain modulation

Background

Conditioned pain modulation (CPM) evaluates the effect of a painful conditioning stimulus (CS) on a painful test stimulus (TS). Using painful cutaneous electrical stimulation (PCES) as TS and painful cold water as CS, the pain relief was paralleled by a decrease in evoked potentials (PCES-EPs). We now aimed to compare the effect of CPM with cognitive distraction on PCES-induced pain and PCES-EP amplitudes.

Methods

PCES was performed using surface electrodes inducing a painful sensation of 60 (NRS 0–100) on one hand. In a crossover design healthy subjects (included: n = 38, analyzed: n = 23) immersed the contralateral hand into 10 °C cold water (CS) for CPM evaluation and performed the 1-back task for cognitive distraction. Before and during the CS and 1-back task, respectively, subjects rated the pain intensity of PCES and simultaneously cortical evoked potentials were recorded.

Results

Both CPM and cognitive distraction significantly reduced PCES-EP amplitudes (CPM: 27.6 ± 12.0 μV to 20.2 ± 9.5 μV, cognitive distraction: 30.3 ± 14.2 µV to 13.6 ± 5.2 μV, p < 0.001) and PCES-induced pain (on a 0–100 numerical rating scale: CPM: 58 ± 4 to 41.1 ± 12.3, cognitive distraction: 58.3 ± 4.4 to 38.0 ± 13.0, p < 0.001), though the changes in pain intensity and PCES-amplitude did not correlate. The changes of the PCES-EP amplitudes during cognitive distraction were more pronounced than during CPM (p = 0.001).

Conclusions

CPM and cognitive distraction reduced the PCES-induced pain to a similar extent. The more pronounced decrease of PCES-EP amplitudes after distraction by a cognitive task implies that both conditions might not represent the general pain modulatory capacity of individuals, but may underlie different neuronal mechanisms with the final common pathway of perceived pain reduction.

Painful Cutaneous Electrical Stimulation vs. Heat Pain as Test Stimuli in Conditioned Pain Modulation

Different paradigms can assess the effect of conditioned pain modulation (CPM). The aim of the present study was to compare heat pain, as an often used test stimulus (TS), to painful cutaneous electrical stimulation (PCES), having the advantage of the additional recording of PCES-related evoked potentials. In 28 healthy subjects we applied heat and PCES at the dominant hand as test stimulus (TS) to compare the CPM-effect elicited by hand immersion into cold water (10 °C) as conditioning stimulus (CS). Subjects rated the pain intensity of TS at baseline, during and 5 min after CS application and additionally of CS, on a numerical rating scale (NRS) (0–100). The ‘early’ (during CS–before CS) and ‘late’ (after CS–before CS) CPM-effects were analyzed. Parallel to the PCES, the related evoked potentials were recorded via Cz to evaluate any changes in PCES-amplitudes. CS reduced significantly the pain intensity of both PCES and heat pain as TS. On a group level, the CPM-effect did not differ significantly between both paradigms. Both early and late CPM-effect based on PCES correlated significantly with the CS pain intensity (r = −0.630 and −0.503, respectively), whereas using heat pain the correlation was not significant. We found a significant reduction of PCES-amplitudes during CS, but this did not correlate with the PCES-induced pain intensity. Correlation with the CS painfulness (r = −0.464) did not achieve the significance level after Bonferroni correction. The extent of the CPM effects was similar in both testing paradigms at group level, despite intraindividual differences. Future studies should further elicit the exact mechanisms explaining the modality of these specific differences.

The effect of Virtual Reality on evoked potentials following painful electrical stimuli and subjective pain

BACKGROUND

Virtual reality (VR) has been shown to reduce pain, however outcome parameters of previous studies have primarily been of a subjective nature and susceptible to bias. This study investigated the effect of VR on cortical processing of evoked potentials (EPs) and subjectively reported pain. Additionally, we explored whether subjects' demographic and personal characteristics modulated the effect of VR analgesia.

METHODS

Three VR conditions were compared in a randomized cross-over study of 30 healthy volunteers: Passive VR (i.e. no interaction possible with the virtual world), active VR (interactive virtual environment) and no VR (black screen). Subjects received noxious electrical stimuli at random intervals during all conditions. EPs, recorded at Cz, were extracted time locked to stimuli. Pain scores were reported after each condition.

RESULTS

Active VR significantly decreased pain scores and amplitudes of N1 and P3. Passive VR had no analgesic effect. Age was significantly correlated to pain scores, with older subjects demonstrating larger effects of VR. Gender, game experience, and susceptibility for immersion, did not influence VR analgesia.

CONCLUSION

Active VR decreases pre-perceptual and perceptual brain activity following painful electrical stimuli, corresponding with reduced pain experience. VR has potential to serve as a non-pharmacologic treatment for pain, particularly in elderly patients.

Exposure to Odors Increases Pain Threshold in Chronic Low Back Pain Patients

Objectives

Structured exposure to odors is an acknowledged therapy in patients with smell loss but has also been shown to be effective in depression. The latter might rely on connections between olfactory and emotional structures, suggesting possible effects of a similar approach in pain patients. Based on neuroanatomy, there are several interfaces between the “pain matrix” and olfactory system, such as the limbic system, hypothalamus, and mediodorsal thalamus. We aimed to investigate whether structured exposure to odors may impact perceived pain in patients with chronic low back pain.

Design

Randomized controlled parallel-group design. Subjects were tested on two occasions, at baseline and after four weeks.

Setting

Ambulatory.

Subjects

Forty-two patients with chronic low back pain

Methods

For all patients, olfactory function (using the “Sniffin’Sticks” test kit), detection, and pain thresholds for cutaneous electrical stimuli (applied to the forearm) were tested at baseline and after four weeks. Twenty-eight patients exposed themselves to four odors (rose, vanilla, chocolate, peach) every two hours over a period of four weeks (training group). Control patients (N = 14) underwent no such “olfactory training” (nontraining group).

Results

Pain thresholds were significantly increased in patients who performed olfactory training compared with patients who did not train with odors. Detection thresholds and olfactory function remained unchanged.

Conclusions

The present results indicate that regular exposure to odors increases pain thresholds in patients with chronic back pain and could be useful for general pain control in these patients. Furthermore, olfactory training in chronic pain patients might help to reduce chronification of pain by desensitization.

Pain-related evoked potentials in patients with large, mixed, and small fiber neuropathy

OBJECTIVE

To investigate A-delta fiber pathways in patients with large, mixed, and small fiber neuropathies using pain-related evoked potentials (PREP).

METHODS

We prospectively examined consecutive and unselected 108 patients with neuropathies using PREP. Patients were stratified according to impaired fiber types in those with large fiber neuropathy (LFN, n = 23), mixed fiber neuropathy (MFN, n = 80), and small fiber neuropathy (SFN, n = 5). Additionally, medical history, nerve conduction studies, quantitative sensory testing (QST), and skin punch biopsy were applied. Data was compared with those of 49 healthy controls.

RESULTS

Patients with MFN showed a distal loss of PREP (16/80, 20%) and prolonged PREP latencies after stimulation at the foot (MFN: 225.8 [135-293.6] ms, controls: 218 [135-394] ms, p < 0.05). Patients with demyelinating neuropathies had prolonged PREP latencies after stimulation at the hand (p < 0.05 each). QST showed an impairment of small and large fiber function in patients with MFN. PREP were mostly absent in patients at advanced stages of neuropathies: in 10/31 (30%) patients with no recordable sural nerve action potential (SNAP, preserved SNAP: 8/76, 10% missing) and in 4/17 (24%) patients with loss of distal epidermal innervation (preserved epidermal innervation: 7/60, 24%) PREP was not recordable. PREP peak-to-peak amplitude after stimulation at the face was lowered in patients with reduced proximal intraepidermal nerve fiber density (p < 0.02).

CONCLUSION

PREP is a useful screening method for A-delta fiber pathology also in patients with simultaneous large fiber pathology. Loss of PREP indicates advance stages of nerve fiber damage.

SIGNIFICANCE

PREP may be useful as a complementary method for detection of small fiber impairment also in patients with mixed fiber neuropathy and in advanced stages.

Clinical neurophysiology of pain

Clinical neurophysiologic investigation of pain pathways in humans is based on specific techniques and approaches, since conventional methods of nerve conduction studies and somatosensory evoked potentials do not explore these pathways. The proposed techniques use various types of painful stimuli (thermal, laser, mechanical, or electrical) and various types of assessments (measurement of sensory thresholds, study of nerve fiber excitability, or recording of electromyographic reflexes or cortical potentials). The two main tests used in clinical practice are quantitative sensory testing and pain-related evoked potentials (PREPs). In particular, PREPs offer the possibility of an objective assessment of nociceptive pathways. Three types of PREPs can be distinguished depending on the type of stimulation used to evoke pain: laser-evoked potentials, contact heat evoked potentials, and intraepidermal electrical stimulation evoked potentials (IEEPs). These three techniques investigate both small-diameter peripheral nociceptive afferents (mainly Aδ nerve fibers) and spinothalamic tracts without theoretically being able to differentiate the level of lesion in the case of abnormal results. In routine clinical practice, PREP recording is a reliable method of investigation for objectifying the existence of a peripheral or central lesion or loss of function concerning the nociceptive pathways, but not the existence of pain. Other methods, such as nerve fiber excitability studies using microneurography, more directly reflect the activities of nociceptive axons in response to provoked pain, but without detecting or quantifying the presence of spontaneous pain. These methods are more often used in research or experimental study design. Thus, it should be kept in mind that most of the results of neurophysiologic investigation performed in clinical practice assess small fiber or spinothalamic tract lesions rather than the neuronal mechanisms directly at the origin of pain and they do not provide objective quantification of pain.

Bilaterally prolonged latencies of pain-related evoked potentials in peripheral nerve injuries

OBJECTIVE

Cross-sectional study to test the applicability of pain-related evoked potentials (PREP) for the diagnosis of peripheral nerve injuries (PNI).

INTRODUCTION

Patients with generalized polyneuropathies show prolonged latencies and decreased amplitudes of PREP indicating an impairment of A-delta fibers. Although these fibers are frequently affected in PNI, it is unclear, if PREP-testing detects PNI comparable to Nerve Conduction Studies (NCS).

METHODS

23 patients with PNI of one upper limb underwent bilateral PREP-testing (using concentric surface electrodes) and NCS. 41 healthy controls underwent PREP-testing only. We determined pain thresholds, N1-latencies and N1P1-amplitudes of PREP and analyzed them for group and side-to-side differences. Small-fiber function was evaluated using thermal detection thresholds of Quantitative Sensory Testing (QST). N1-latencies above a cut-off calculated by ROC-analysis were defined as abnormal in order to compare detection rates of PREP and NCS.

RESULTS

Patients with PNI showed bilaterally prolonged N1-latencies (ipsilateral: 167.0 ± 40.7 ms vs. 141.2 ± 20.5 ms / contralateral: 160.0 ± 41.0 ms vs. 140.2 ± 23.9 ms) without a significant side-to-side difference. Pain thresholds were increased on the affected side only (4.6 ± 5.2 mA vs. 2.4 ± 1.4 mA (controls)). N1P1-amplitudes did not differ between patients and controls. 7 (32%) patients showed prolonged N1-latencies (>176 ms) of PREP. NCS were abnormal in 16 (73%) cases. 13 (59%) patients showed thermal hypoesthesia in QST.

CONCLUSION

Contrary to our expectations, we found bilaterally prolonged N1-latencies and normal N1P1-amplitudes in patients with PNI. Our findings support the hypothesis of a bilateral generation of PREP and indicate that PREP are not suitable for the diagnosis of PNI.

Clinical utility of contact heat evoked potentials (CHEPs) in a case of mentalis nerve lesion

•

Assessment of lesions presenting with neuropathic pain requires specific techniques.

•

Brainstem reflexes may not be sufficient to demonstrate a neuropathic lesion.

•

Reduced size of nociceptive evoked potentials was the only abnormality found in a case of facial pain.

Objective

Nociceptive evoked potentials are still infrequently used in electrodiagnostic studies of single patients. We report a case in which the results of contact heat evoked potentials (CHEPs) provided unique information for the diagnosis.

Methods

After biopsy for a local cementoma, a 21-year-old woman presented with neuropathic pain in the distribution of her left mentalis nerve. A CT scan showed a well circumscribed lesion near the mentalis nerve groove. We examined brainstem reflexes and evoked potentials conveyed through the mentalis nerve.

Results

Blink reflex responses recorded from the orbicularis oculi, jaw jerk and masseteric silent period recorded from the masseter muscles and long latency evoked potentials recorded from Cz to electrical stimulation of the mentalis nerve were all within normal values, with no differences between sides. However, CHEPs, recorded from Cz to thermoalgesic stimulation of the left mentalis area were decreased to approximately 1/3 their size in comparison to stimulation to the unaffected side.

Conclusion

While the patient reported symptoms and had neuroimaging signs of mentalis neuropathy, the sole electrophysiological abnormality identified was that of CHEPs, which specifically test small, unmyelinated fibers.

Significance

Nociceptive evoked potentials can provide unique information on damage of small nerve fibers in specific cases.

The Availability of Quantitative Assessment of Pain Perception in Patients With Diabetic Polyneuropathy

Objective

To evaluate the usefulness of the quantitative assessment of pain perception (QAPP) in diabetic polyneuropathy (DPN) patients.

Methods

Thirty-two subjects with DPN were enrolled in this study. The subjects’ pain perception was assessed quantitatively. Current perception threshold (CPT) and pain equivalent current (PEC) were recorded. All patients were tested with a nerve conduction study (NCS) for evaluation of DPN and pain-related evoked potential (PREP) for evaluation of small fiber neuropathy (SFN) on bilateral upper and lower limbs. All patients were asked to participate in tests such as visual analogue scale (VAS) and SF-36 Health Survey Version 2 to evaluate their subjective pain and quality of life, respectively.

Results

The PEC of QAPP showed significant correlations with VAS (p=0.002) and physical function surveyed with SF-36 Health Survey Version 2 (p=0.035). The results of QAPP had no correlation with NCS, but there was a significant relationship between the CPT of QAPP and PREP (p=0.003).

Conclusion

The QAPP may be useful not only in providing objective evaluations of subjective pain in patients with DPN but also in the assessment of diabetic SFN.

Pain Processing in a Social Context and the Link with Psychopathic Personality Traits-An Event-Related Potential Study

Empathy describes the ability to understand another person's feelings. Psychopathy is a disorder that is characterized by a lack of empathy. Therefore, empathy and psychopathy are interesting traits to investigate with respect to experiencing and observing pain. The present study aimed to investigate pain empathy and pain sensitivity by measuring event-related potentials (ERPs) extracted from the ongoing EEG in an interactive setup. Each participant fulfilled subsequently the role of "villain" and "victim". In addition, mode of control was modulated resulting in four different conditions; passive villain, active villain, active victim and passive victim. Response-, visual- and pain ERPs were compared between the four conditions. Furthermore, the role of psychopathic traits in these outcomes was investigated. Our findings suggested that people experience more conflict when hurting someone else than hurting themselves. Furthermore, our results indicated that self-controlled pain was experienced as more painful than uncontrolled pain. People that scored high on psychopathic traits seemed to process and experience pain differently. According to the results of the current study, social context, attention and personality traits seem to modulate pain processing and the empathic response to pain in self and others. The within-subject experimental design described here provides an excellent approach to further unravel the influence of social context and personality traits on social cognition.

Evoked potentials after painful cutaneous electrical stimulation depict pain relief during a conditioned pain modulation

BACKGROUND

Conditioned pain modulation (CPM) evaluates the pain modulating effect of a noxious conditioning stimulus (CS) on another noxious test stimulus (TS), mostly based solely on subjective pain ratings. We used painful cutaneous electrical stimulation (PCES) to induce TS in a novel CPM-model. Additionally, to evaluate a more objective parameter, we recorded the corresponding changes of cortical evoked potentials (PCES-EP).

METHODS

We examined the CPM-effect in 17 healthy subjects in a randomized controlled cross-over design during immersion of the non-dominant hand into 10 °C or 24 °C cold water (CS). Using three custom-built concentric surface electrodes, electrical stimuli were applied on the dominant hand, inducing pain of 40-60 on NRS 0-100 (TS). At baseline, during and after CS we assessed the electrically induced pain intensity and electrically evoked potentials recorded over the central electrode (Cz).

RESULTS

Only in the 10 °C-condition, both pain (52.6 ± 4.4 (baseline) vs. 30.3 ± 12.5 (during CS)) and amplitudes of PCES-EP (42.1 ± 13.4 μV (baseline) vs. 28.7 ± 10.5 μV (during CS)) attenuated during CS and recovered there after (all p < 0.001). In the 10 °C-condition changes of subjective pain ratings during electrical stimulation and amplitudes of PCES-EP correlated significantly with each other (r = 0.5) and with CS pain intensity (r = 0.5).

CONCLUSIONS

PCES-EPs are a quantitative measure of pain relief, as changes in the electrophysiological response are paralleled by a consistent decrease in subjective pain ratings. This novel CPM paradigm is a feasible method, which could help to evaluate the function of the endogenous pain modulation processes.

TRIAL REGISTRATION

German Clinical Trials Register DRKS-ID: DRKS00012779 , retrospectively registered on 24 July 2017.

Exploring pain pathophysiology in patients

Although animal models of pain have brought invaluable information on basic processes underlying pain pathophysiology, translation to humans is a problem. This Review will summarize what information has been gained by the direct study of patients with chronic pain. The techniques discussed range from patient phenotyping using quantitative sensory testing to specialized nociceptor neurophysiology, imaging methods of peripheral nociceptors, analyses of body fluids, genetics and epigenetics, and the generation of sensory neurons from patients via inducible pluripotent stem cells.

Psychopharmacological modulation of event-related potentials suggests that first-hand pain and empathy for pain rely on similar opioidergic processes

Accumulating evidence suggests that empathy for pain recruits similar neural processes as the first-hand experience of pain. The pain-related P2, an event-related potential component, has been suggested as a reliable indicator of neural processes associated with first-hand pain. Recent evidence indicates that placebo analgesia modulates this component for both first-hand pain and empathy for pain. Moreover, a psychopharmacological study showed that administration of an opioid antagonist blocked the effects of placebo analgesia on self-report of both first-hand pain and empathy for pain. Together, these findings suggest that the opioid system plays a similar role during first-hand pain and empathy for pain. However, such a conclusion requires evidence showing that neural activity during both experiences is similarly affected by psychopharmacological blockage of opioid receptors. Here, we measured pain-related P2 amplitudes and self-report in a group of participants who first underwent a placebo analgesia induction procedure. Then, they received an opioid receptor antagonist known to block the previously induced analgesic effects. Self-report showed that blocking opioid receptors after the induction of placebo analgesia increased both first-hand pain and empathy for pain, replicating previous findings. Importantly, P2 amplitudes were also increased during both experiences. Thus, the present findings extend models proposing that empathy for pain is partially grounded in first-hand pain by suggesting that this also applies to the underlying opioidergic neurochemical processes.

High test-retest-reliability of pain-related evoked potentials (PREP) in healthy subjects

Pain-related evoked potentials (PREP) is an established electrophysiological method to evaluate the signal transmission of electrically stimulated A-delta fibres. Although prerequisite for its clinical use, test-retest-reliability and side-to-side differences of bilateral stimulation in healthy subjects have not been examined yet. We performed PREP twice within 3-14days in 33 healthy subjects bilaterally by stimulating the dorsal hand. Detection (DT) and pain thresholds (PT) after electrical stimulation, the corresponding pain ratings, latencies of P0, N1, P1 and N2 components and the corresponding amplitudes were assessed. Impact of electrically induced pain intensity, age, sex, and arm length on PREP was analysed. MANOVA, t-Test, interclass correlation coefficient (ICC), standard error of measurement (SEM), smallest real difference (SRD), Bland-Altmann-Analysis as well as ANCOVA were used for statistical analysis. Measurement from both sides on both days resulted in mean N1-latencies from 142.39±18.12ms to 144.03±16.62ms and in mean N1P1-amplitudes from 39.04±12.26μV to 40.53±12.9μV. Analysis of a side-to-side effect showed for the N1-latency a F-value of 0.038 and for the N1P1-amplitude of 0.004 (p>0.8). We found intraclass correlation coefficients (ICC) from 0.88 to 0.93 and a standard error of measurement (SEM)<10% of mean values for all measurements concerning the N1-Latency and N1P1-amplitude. Intraclass correlation coefficients, standard error of measurement and Bland-Altman-Analyses revealed excellent test-retest-reliability for N1-latency and N1P1-amplitude without systematic error and there was no side-to-side effect on PREP. N1-latency (r=0.35, p<0.05) and N1P1-amplitude (r=-0.45, p<0.05) correlated with age and additionally N1-latency correlated with arm length (r=0.45, p<0.001). In contrast, pain intensity during the stimulation had no effect on both N1-latency and N1P1-amplitude. In summary, PREP showed high test-retest-reliability and negligible side-to-side differences concerning the commonly used parameters N1-latency and N1P1-amplitude.

Small Fiber Neuropathy in Children: Two Case Reports Illustrating the Importance of Recognition

Small fiber neuropathy (SFN) is a debilitating condition that often leads to pain and autonomic dysfunction. In the last few decades, SFN has been gaining more attention, particularly in adults. However, literature about SFN in children remains limited. The present article reports the cases of 2 adolescent girls diagnosed with SFN. The first patient (14 years of age) complained about painful itch and tingling in her legs, as well as dysautonomia symptoms for years. She also reported a red/purple-type discoloration of her legs aggravated by warmth and standing, compatible with erythromelalgia. The diagnosis of SFN was confirmed by a reduced intraepidermal nerve fiber density (IENFD) in skin biopsy sample. No underlying conditions were found. Symptomatic neuropathic pain treatment was started with moderate effect. The second patient (16 years of age) developed painful sensations in both feet and hands 6 weeks after an ICU admission for diabetic ketoacidosis, which included dysautonomia symptoms. She also exhibited some signs of erythromelalgia. The patient was diagnosed with predominant SFN (abnormal IENFD and quantitative sensory testing) as well as minor large nerve fiber involvement. Treatment with duloxetine, combined with a rehabilitation program, resulted in a marked improvement in her daily functioning. Although the SFN diagnosis in these 2 cases could be established according to the definition of SFN used in adults, additional diagnostic tools are needed that may be more appropriate for children. Additional information about the course of SFN in children may result in better treatment options.

Amplitudes of Pain-Related Evoked Potentials Are Useful to Detect Small Fiber Involvement in Painful Mixed Fiber Neuropathies in Addition to Quantitative Sensory Testing - An Electrophysiological Study

To investigate the usefulness of pain-related evoked potentials (PREP) elicited by electrical stimulation for the identification of small fiber involvement in patients with mixed fiber neuropathy (MFN). Eleven MFN patients with clinical signs of large fiber impairment and neuropathic pain and ten healthy controls underwent clinical and electrophysiological evaluation. Small fiber function, electrical conductivity and morphology were examined by quantitative sensory testing (QST), PREP, and skin punch biopsy. MFN was diagnosed following clinical and electrophysiological examination (chronic inflammatory demyelinating neuropathy: n = 6; vasculitic neuropathy: n = 3; chronic axonal ­neuropathy: n = 2). The majority of patients with MFN characterized their pain by descriptors that mainly represent C-fiber-mediated pain. In QST, patients displayed elevated cold, warm, mechanical, and vibration detection thresholds and cold pain thresholds indicative of MFN. PREP amplitudes in patients correlated with cold (p < 0.05) and warm detection thresholds (p < 0.05). Burning pain and the presence of par-/dysesthesias correlated negatively with PREP amplitudes (p < 0.05). PREP amplitudes correlating with cold and warm detection thresholds, burning pain, and par-/dysesthesias support employing PREP amplitudes as an additional tool in conjunction with QST for detecting small fiber impairment in patients with MFN.

Botulinum neurotoxin type A in the treatment of classical Trigeminal Neuralgia (BoTN): study protocol for a randomized controlled trial

BACKGROUND

Trigeminal neuralgia is characterized by paroxysmal facial pain attacks. Adequate prophylactic drug therapy is often limited by the lack of efficacy and intolerance due to central nervous system side effects. Subcutaneous injections of botulinum toxin type A are a promising treatment option for patients with unsatisfactory response to drug therapy or neurosurgical intervention. Its effects are expected to last for at least 3 months, so it could be a potential long-term treatment. This is the study protocol of a prospective, placebo-controlled, double blind clinical trial investigating the add-on therapy of subcutaneous administration of botulinum toxin type A injections to standard treatment in therapy-refractory classical trigeminal neuralgia.

METHODS AND DESIGN

BoTN is a prospective, double blind, placebo-controlled trial with a randomized withdrawal design in which a single blind phase is followed by a double blind phase (see also Methods and design). Eligible patients with classical trigeminal neuralgia who are otherwise refractory to medical and neurosurgical treatment will receive subcutaneous injections of botulinum toxin type A into injection sites of the affected trigeminal branch. In the first phase all patients will receive botulinum toxin type A in a single blinded intervention. Twelve weeks later therapy responders will be allocated to the verum or placebo (saline) arm in a double blind, randomized manner. These injections will be performed at the same sites as the first injections. This trial will be conducted in a tertiary outpatient clinic specialized in the treatment of headache and facial pain. There will be three investigators performing the injections who are experienced in the treatment of headache and facial pain and trained in botulinum toxin type A injections.

DISCUSSION

BoTN is designed to assess the efficacy and safety of subcutaneous botulinum toxin type A injections in addition to standard prophylactic treatment in therapy-refractory trigeminal neuralgia.

TRIAL REGISTRATION NUMBER

EU Clinical Trials Register: EudraCT-No: 2014-001959-24 https://www.clinicaltrialsregister.eu/ctr-search/rest/download/trial/2014-001959-24/DE Date of trial registration 26 August 2014.