Rationale and Evidence for Peripheral Nerve Stimulation for Treating Essential Tremor.

Background: There is growing recognition of peripheral stimulation techniques for controlling arm symptoms in essential tremor (ET). Recently, the FDA gave clearance to the Cala system, a device worn around the wrist to treat arm tremors. The Cala system stimulates the sensory afferents of the peripheral nerves with high-frequency pulses. These pulses are delivered to the median and radial nerves alternately at the tremor frequency of the individual patient. Methods: The PubMed database was searched using the terms ("Essential Tremor"[Mesh] OR "essential tremor" [Title/Abstract] OR "tremor" [Title/Abstract]) AND ("peripheral arm stimulation" [Title/Abstract] OR "Cala device" [Title/Abstract] OR "sensory afferent stimulation" [Title/Abstract] OR "afferent stimulation" [Title/Abstract] OR "arm stimulation" [Title/Abstract] OR "peripheral nerve stimulation" [Title/Abstract]). Results: The search yielded 54 articles. Many studies discussed the rationale and various strategies for peripheral modulation of tremor. While the Cala system was found to be safe and well-tolerated in ET, data on efficacy revealed mixed findings. In a large randomized, blinded trial (n = 77), the primary outcome evaluated with spiral drawing task did not improve but the secondary outcomes reflected by the arm tremor severity and the activities of the daily living score revealed 20-25% improvements. A subsequent trial (n = 323) found that the in-home use of the Cala device led to improvements of similar magnitude lasting for at least three months but the clinical assessments were open-labeled. Discussion: Peripheral stimulation techniques are promising therapeutic modalities for treating ET symptoms. Stimulation of sensory afferent nerve fibers at the wrist can potentially modulate the peripheral and central components of the tremor network. Although the Cala system is user-friendly, safe, and well-tolerated, the current clinical evidence on the efficacy is inconsistent and insufficient. Thus, more data is warranted for implementing peripheral nerve stimulation as a standard of care for ET. Highlights: The current review discusses the rationale, background, and potential mechanisms for using peripheral arm stimulation devices for treating ET. The Cala system is a wrist-worn peripheral nerve stimulation device that received FDA clearance to treat arm tremors. The current review evaluates the evidence for the safety and efficacy of using the Cala system and similar devices in clinical practice.

Is Dry Needling of the Supinator a Safe Procedure? A Potential Treatment for Lateral Epicondylalgia or Radial Tunnel Syndrome. A Cadaveric Study.

The supinator muscle is involved in two pain conditions of the forearm and wrist: lateral epicondylalgia and radial tunnel syndrome. Its close anatomical relationship with the radial nerve at the arcade of Frohse encourages research on dry needling approaches. Our aim was to determine if a solid filiform needle safely penetrates the supinator muscle during the clinical application of dry needling. Needle insertion of the supinator muscle was conducted in ten cryopreserved forearm specimens with a 30 × 0.32 mm filiform needle. With the forearm pronated, the needle was inserted perpendicular into the skin at the dorsal aspect of the forearm at a point located 4cm distal to the lateral epicondyle. The needle was advanced to a depth judged to be in the supinator muscle. Safety was assessed by measuring the distance from the needle to the surrounding neurovascular bundles of the radial nerve. Accurate needle penetration of the supinator muscle was observed in 100% of the forearms (needle penetration:16.4 ± 2.7 mm 95% CI 14.5 mm to 18.3 mm). No neurovascular bundle of the radial nerve was pierced in any of the specimen's forearms. The distances from the tip of the needle were 7.8 ± 2.9 mm (95% CI 5.7 mm to 9.8 mm) to the deep branch of the radial nerve and 8.6 ± 4.3 mm (95% CI 5.5 mm to 11.7 mm) to the superficial branch of the radial nerve. The results from this cadaveric study support the assumption that needling of the supinator muscle can be accurately and safely conducted by an experienced clinician.

Lateral epicondylitis: Are we missing out on radial nerve involvement? A cross-sectional study.

INTRODUCTION: Lateral epicondylitis (LE) is a common ailment causing pain and functional limitations. There is an inadequate understanding of its etiopathogenesis. Involvement of the radial nerve (RN) as the primary causative factor for this condition remains debatable. The aim of the present study was to assess the RN thickness in patients with LE and compare it with the unaffected side. METHODS: The study included seventy eligible patients (M:F, 22:48) in the age group of 30-60 years with a clinical diagnosis of LE. The cross-sectional area of RN was measured at the spiral groove (SG) and around the antecubital fossa (AF) using ultrasound and compared with the unaffected side. Numeric Pain Rating Scale (NPRS) and the QuickDASH scale were used to assess pain and functional impairment. RESULTS: Thickness of RN at the AF (p = 0.026) and the SG (p = 0.0117) on the affected were statistically significant compared to the unaffected side in the cohort comprising of all the 70 patients. Out of 70 patients, increased thickness was seen in 23 at the SG and 19 at the AF. QuickDASH was statistically significant in patients who had thickened nerves compared to the unaffected side at the SG (p = 0.04) but not at the AF (p = 0.16). NPRS was not statistically significant at either the AF (p = 0.34) or the SG (p = 0.71) in patients with thickened nerves. CONCLUSION: Tennis elbow needs to be no longer acknowledged only as tendinopathy. It also requires consideration of the involvement of the RN.

Brain Metabolic Changes with Longitudinal Transcutaneous Afferent Patterned Stimulation in Essential Tremor Subjects.

Background: Non-invasive peripheral nerve stimulation, also referred to as transcutaneous afferent patterned stimulation (TAPS), reduces hand tremor in essential tremor (ET) subjects. However, the mechanism of action of TAPS is unknown. Here, we investigated changes in brain metabolism over three months of TAPS use in ET subjects. Methods: This was an interventional, open label, single group study enrolling 5 ET subjects. They received 40 minutes of TAPS treatment twice daily for 90 days. Brain metabolic activity and tremor severity were measured using 18F-fluorodeoxyglucose (FDG) PET/CT, and the Tremor Research Group Essential Tremor Rating Assessment Scale (TETRAS), respectively, at baseline and after 90 days. Tremor power and frequency was measured before and after all TAPS sessions using an onboard three-axis accelerometer. Results: FDG PET/CT revealed areas of hypermetabolism in ipsilateral cerebellar hemisphere and hypometabolism in contralateral cerebellar hemisphere following 90 days of TAPS treatment, compared to day one (uncorrected p value <0.05). Paired pre-post kinematic measurements over 90 days showed significantly decreased tremor power (p < 0.0001) but no change in tremor frequency. The TETRAS score on day 1 decreased from 6.5 ± 2.5 to 4.1 ± 1.8 following TAPS (p = 0.05). The pre-post TETRAS scores on day 90: 4.9 ± 1.5 and 4.1± 1 were lower than pre-TAPS TETRAS score on day 1 (p = 0.14 and 0.05, respectively). Conclusions: Our results suggest that longitudinal TAPS of the median and radial nerves modulates brain metabolism in areas instrumental to motor coordination and implicated in ET. Clinically, TAPS reduced tremor power, but had no effect on tremor frequency. This study paves the way for comprehensive studies in larger cohorts to further elucidate the mechanism of TAPS. Highlights: Non-invasive peripheral nerve stimulation, also referred to as transcutaneous afferent patterned stimulation (TAPS), reduces hand tremor in essential tremor subjects. Longitudinal TAPS therapy alters cerebellar metabolism, which can be a cause or consequence of tremor reduction. Cerebellar-premotor region connectivity may play a role in the anti-tremor effects of TAPS.

Prospective Home-use Study on Non-invasive Neuromodulation Therapy for Essential Tremor.

Highlights: This prospective study is one of the largest clinical trials in essential tremor to date. Study findings suggest that individualized non-invasive neuromodulation therapy used repeatedly at home over three months results in safe and effective hand tremor reduction and improves quality of life for many essential tremor patients. Background: Two previous randomized, controlled, single-session trials demonstrated efficacy of non-invasive neuromodulation therapy targeting the median and radial nerves for reducing hand tremor. This current study evaluated efficacy and safety of the therapy over three months of repeated home use. Methods: This was a prospective, open-label, post-clearance, single-arm study with 263 patients enrolled across 26 sites. Patients were instructed to use the therapy twice daily for three months. Pre-specified co-primary endpoints were improvements on clinician-rated Tremor Research Group Essential Tremor Rating Assessment Scale (TETRAS) and patient-rated Bain & Findley Activities of Daily Living (BF-ADL) dominant hand scores. Other endpoints included improvement in the tremor power detected by an accelerometer on the therapeutic device, Clinical and Patient Global Impression scores (CGI-I, PGI-I), and Quality of Life in Essential Tremor (QUEST) survey. Results: 205 patients completed the study. The co-primary endpoints were met (p≪0.0001), with 62% (TETRAS) and 68% (BF-ADL) of 'severe' or 'moderate' patients improving to 'mild' or 'slight'. Clinicians (CGI-I) reported improvement in 68% of patients, 60% (PGI-I) of patients reported improvement, and QUEST improved (p = 0.0019). Wrist-worn accelerometer recordings before and after 21,806 therapy sessions showed that 92% of patients improved, and 54% of patients experienced ≥50% improvement in tremor power. Device-related adverse events (e.g., wrist discomfort, skin irritation, pain) occurred in 18% of patients. No device-related serious adverse events were reported. Discussion: This study suggests that non-invasive neuromodulation therapy used repeatedly at home over three months results in safe and effective hand tremor reduction in many essential tremor patients.

Selective neural electrical stimulation restores hand and forearm movements in individuals with complete tetraplegia.

BACKGROUND: We hypothesized that a selective neural electrical stimulation of radial and median nerves enables the activation of functional movements in the paralyzed hand of individuals with tetraplegia. Compared to previous approaches for which up to 12 muscles were targeted through individual muscular stimulations, we focused on minimizing the number of implanted electrodes however providing almost all the needed and useful hand movements for subjects with complete tetraplegia. METHODS: We performed acute experiments during scheduled surgeries of the upper limb with eligible subjects. We scanned a set of multicontact neural stimulation cuff electrode configurations, pre-computed through modeling simulations. We reported the obtained isolated and functional movements that were considered useful for the subject (different grasping movements). RESULTS: In eight subjects, we demonstrated that selective stimulation based on multicontact cuff electrodes and optimized current spreading over the active contacts provided isolated, compound, functional and strong movements; most importantly 3 out of 4 had isolated fingers or thumb flexion, one patient performed a Key Grip, another one the Power and Hook Grips, and the 2 last all the 3 Grips. Several configurations were needed to target different areas within the nerve to obtain all the envisioned movements. We further confirmed that the upper limb nerves have muscle specific fascicles, which makes it possible to activate isolated movements. CONCLUSIONS: The future goal is to provide patients with functional restoration of object grasping and releasing with a minimally invasive solution: only two cuff electrodes above the elbow. Ethics Committee / ANSM clearance prior to the beginning of the study (inclusion period 2016-2018): CPP Sud Méditerranée, #ID-RCB:2014-A01752-45, first acceptance 10th of February 2015, amended 12th of January 2016. TRIAL REGISTRATION: (www.clinicaltrials.gov): #NCT03721861, Retrospectively registered on 26th of October 2018.

Elicited Finger and Wrist Extension Through Transcutaneous Radial Nerve Stimulation.

Individuals with neurological disorders, such as stroke or spinal cord injury, often have weakness and/or spasticity in their hand and wrist muscles, which can lead to impaired ability to extend their fingers and wrists. Functional electrical stimulation can help to restore these motor functions. However, the conventional stimulation method can lead to fast muscle fatigue and limited movements due to a non-physiological recruitment of motor units and a limited recruitment of deep muscles. In this paper, we investigated the feasibility of eliciting various hand opening and wrist extension movement patterns through a transcutaneous electrical stimulation array, which targeted the proximal segment of the radial nerve bundle proximal to the elbow. The wrist and finger joint kinematics were used to classify the different movement patterns through a cluster analysis, and electromyogram signals from the wrist and finger extensors were recorded to investigate the muscle activation patterns. The results showed that the finger and wrist motions can be elicited both independently and in a coordinated manner, by changing the stimulation intensity and stimulation location. H-reflex activity was also observed, which demonstrated the potential of recruiting motor units in a physiological order. Our approach could be further developed into a rehabilitative/assistive tool for individuals with impaired hand opening and/or wrist extension.

Does Frequency Modulation of Transcutaneous Electrical Nerve Stimulation Affect Habituation and Mechanical Hypoalgesia? A Randomized, Double-Blind, Sham-Controlled Crossover Trial.

BACKGROUND: Devices for applying transcutaneous electrical nerve stimulation (TENS) use numerous frequency modulation patterns for decreasing habituation to currents. However, there is no evidence supporting the use of an optimal pattern instead of the others, or even modulated frequencies instead of a fixed frequency. OBJECTIVE: The objectives of this study were to determine the effects of 3 TENS patterns (fixed frequency, random modulation, and 6-second-6-second [6s-6s] modulation) on habituation, to examine the subjective perception of habituation and comfort, and to determine their effects on the mechanical pain threshold (MPT). DESIGN: This study was a randomized, double-blind, sham-controlled crossover trial. SETTING: The study took place in a university research laboratory under attenuated noise conditions at a regulated temperature of 22°C to 26°C. PARTICIPANTS: Thirty-nine volunteers who were healthy participated in this trial. INTERVENTION: The participants received 4 different TENS interventions (fixed frequency, random modulation, 6s-6s modulation, and sham) in random order, with a 24-hour washout period, on the radial nerve. MEASUREMENTS: The main outcome-habituation-was quantified by the increase in current density and the number of times the intensity had to be increased during the session. Secondary outcome variables were subjective perception of habituation and comfort and MPT. RESULTS: Random modulation reduced the number of times the intensity had to be increased because of habituation compared with no modulation (1.6 times; 95% confidence interval [CI] = 0.7-2.6) and 6s-6s modulation (0.8 times; 95% CI = 0.01-1.6). No differences were observed between interventions in terms of an increase in current density, self-perceived habituation, or self-perceived comfort. MPT increased during the intervention in the random-modulation group (4.4 N; 95% CI = 1.8-7.0) and the no-modulation group (5.9 N; 95% CI = 1.9-10.0); there were no significant changes in the other 2 groups. LIMITATIONS: The success of masking or blinding procedures of the participants was not assessed. CONCLUSIONS: Randomly modulated frequencies caused less habituation than nonmodulated frequencies or 6s-6s modulation. Further research on more prolonged (hours-long) interventions in participants with pain is required.

Ultrasound-Guided Percutaneous Electrical Nerve Stimulation of the Radial Nerve for a Patient With Lateral Elbow Pain: A Case Report With a 2-Year Follow-up.

BACKGROUND: Patients with lateral elbow pain are often diagnosed with lateral epicondylalgia. Lateral elbow pain is often associated with dysfunction of the wrist extensor muscles; however, in some cases, it can also mimic signs and symptoms of radial nerve dysfunction. CASE DESCRIPTION: In this case report, a 43-year-old man, who was originally referred with a diagnosis of lateral epicondylalgia as a result of playing table tennis and who previously responded favorably to manual therapy and exercise, presented to the clinic for treatment. An exacerbation while participating in a table tennis match resulted in a return of his lateral epicondylalgia symptoms, which did not respond favorably to the same interventions used in his prior course of therapy. Further examination revealed sensitization of the radial nerve, which was treated with 2 sessions of ultrasound-guided percutaneous electrical nerve stimulation and 4 weeks of a low-load, concentric/eccentric exercise program for the wrist extensors. OUTCOMES: Following this intervention, the patient experienced clinically meaningful improvement in pain intensity (numeric pain-rating scale), function (Patient-Rated Tennis Elbow Evaluation), and related disability (Disabilities of the Arm, Shoulder and Hand questionnaire). The patient progressively exhibited complete resolution of pain and function, which was maintained at 2 years. DISCUSSION: This case report demonstrates the outcomes of a patient with lateral elbow pain who did not respond to manual therapy and exercise. Once radial nerve trunk sensitivity was identified and the intervention, consisting of ultrasound-guided percutaneous electrical nerve stimulation targeting the radial nerve combined with a low-load exercise program, was applied, a full resolution of pain and function occurred rapidly. Future clinical trials should examine the effect of percutaneous electrical nerve stimulation in the management of nerve-related symptoms associated with musculoskeletal pain conditions. LEVEL OF EVIDENCE: Therapy, level 5. J Orthop Sports Phys Ther 2019;49(5):347-354. Epub 18 Jan 2019. doi:10.2519/jospt.2019.8570.

Effect of dry needling on radial tunnel syndrome: A case report.

This case report describes a 45-year-old male who presented with chronic right lateral elbow pain managed unsuccessfully with conservative treatment that included anti-inflammatory medication, injection, massage, exercise, bracing, taping, electro-physical agents, and manual therapy. Diagnosis of radial tunnel syndrome (RTS) was based on palpatory findings, range of motion testing, resisted isometrics, and a positive upper limb neural tension test 2b (radial nerve bias). Conventionally, the intervention for this entrapment has been surgical decompression, with successful outcomes. This is potentially a first-time report, describing the successful management of RTS with dry needling (DN) using a recently published DN grading system. Immediate improvements were noted in all the outcome measures after the first treatment, with complete pain-resolution maintained at a 6-month follow-up. A model is proposed describing the mechanism by which DN could be used to intervene for nerve entrapment interfaces.

Localización biométrica de los puntos motores en el músculo tríceps braquial de individuos brasileños / Biometric location of motor points in the brachial triceps muscle of Brazilian individuals

RESUMEN: El músculo tríceps braquial, es el motor primario para el movimiento de extensión de codo, por lo que una lesión que afecte su función perjudicaría enormemente la calidad de vida de los afectados. El conocimiento de su inervación y la localización biométrica de sus puntos motores, es una herramienta útil en terapias de electro estimulación muscular. El objetivo del estudio fue determinar el número y localización de los puntos motores de este músculo. Para ello, se utilizaron 30 miembros superiores de individuos brasileños, a los cuales se les realizó una disección detallada del compartimiento posterior del brazo. Se registró el número de ramos, puntos motores y localización biométrica de cada uno de los ramos destinados a las cabezas del músculo triceps braquial. Se utilizó como punto de referencia una Línea biepicondilar, trazada entre los epicóndilos humerales. En todos los casos este músculo estaba inervado por el nervio radial. El promedio de puntos motores (PM) para la cabeza larga del músculo (CL) fue de 3,9 ± 1,4; 4,8 ± 1,2 para la cabeza medial (CM) y 4,1 ± 1,4 para la cabeza lateral (CLat). Los puntos motores se concentraron preferentemente en el tercio medio del brazo, tanto a nivel general, como también por cada cabeza. Los datos biométricos aportados complementarán el conocimiento de la inervación de este músculo y favorecerá una mejor comprensión y elección de tratamientos frente a una patología.

SUMMARY: The triceps brachii muscle is the primary motor for elbow extension movement, so a lesion that affects its function would greatly harm the quality of life of those affected. The knowledge of its innervation and the biometric localization of its motor points is a useful tool in electro-stimulation muscular therapies. The objective of the study was to determine the number of branches and location of the motor points of this muscle. To this end, 30 superior members of Brazilian individuals were used, to whom a detailed dissection of the posterior compartment of the arm was performed. The number of branches, motor points and biometric location of each of the branches destined for the three heads of the brachial triceps muscle was recorded. A biepicondilar line, traced between the humeral epicondyles, was used as a reference point. In all cases, this muscle was innervated by the radial nerve. The average motor points for the long head of the muscle (LH) was 3.9 + 1.4; for the medial head (MH) was 4.8 + 1.2 and for the lateral head (LatH) was 4.1+1.4. The motor points were concentrated mainly in the middle third of the arm, both at a general level, and also for each head. The biometric data provided will complement the knowledge of the innervation of this muscle and will favor a better understanding and choice of treatments for a pathology.

Anterior humeral approach with nerve stimulator.

INTRODUCTION: The prevalence of radial nerve injury during surgery is as high as the prevalence of radial nerve injury due to trauma. The aim of this study is to minimize the risk of iatrogenic injury of radial nerve. MATERIALS AND METHODS: Fifty patients with middle or distal diaphysis fractures of humerus and 18 patients with pseudoarthrosis at the same localizations were treated with surgery. Plate-screw fixation was performed with anterior approach in 43 patients. Eleven patients had minimally invasive plate osteosynthesis, and 14 patients had intramedullary nailing. The localization of the radial nerve was determined with nerve stimulator at the area of dissection. RESULTS: Iatrogenic radial nerve injury did not occur in patients treated with open reduction or minimally invasive approach. DISCUSSION: Nerve stimulator may be a method that decreases radial nerve injury, an iatrogenic complication. This method may be used in anterior approach and minimally invasive procedures.

Wireless peripheral nerve stimulation for complex regional pain syndrome type I of the upper extremity: a case illustration introducing a novel technology.

Background Complex regional pain syndrome (CRPS) is a debilitating painful disorder, cryptic in its pathophysiology and refractory condition with limited therapeutic options. Type I CRPS with its variable relationship to trauma has often no discernible fractures or nerve injuries and remains enigmatic in its response to conservative treatment as well as the other limited interventional therapies. Neuromodulation in the form of spinal cord and dorsal root ganglion stimulation (SCS, DRGS) has shown encouraging results, especially of causalgia or CRPS I of lower extremities. Upper extremity CRPS I is far more difficult. Objective To report a case of upper extremity CRPS I treated by wireless peripheral nerve stimulation (WPNS) for its unique features and minimally invasive technique. The system does not involve implantation of battery or its connections. Case report A 47 year old female patient presented with refractory CRPS I following a blunt trauma to her right forearm. As interventional treatment in the form of local anesthetics (Anesthesia of peripheral branches of radial nerve) and combined infusions of ketamine/lidocaine failed to provide any significant relief she opted for WPNS treatment. Based on the topographic distribution, two electrodes (Stimwave Leads: FR4A-RCV-A0 with tines, Generation 1 and FR4A-RCV-B0 with tines, Generation 1), were placed along the course of radial and median nerves under ultrasonography monitoring and guided by intraoperative stimulation. This procedure did not involve implantation of extension cables or the power source. At a frequency of 60 Hz and 300 µs the stimulation induced paresthesia along the distribution of the nerves. Therapeutic relief was observed with high frequency (HF) stimulation (HF 10 kHz/32 µs, 2.0 mA) reducing her pain from a visual analogue scale (VAS) score of 7-4 postoperatively. Three HF stimulations programs were provided at the time of discharge, as she improved in her sensory impairment to touch, pressure and temperature at her first follow up visit. At 5-months she was able to drive, did not require opioids and allodynia disappeared. Conclusions In a case with difficult CRPS I involving upper extremity, a minimally invasive WPNS of radial and median nerves provided good symptomatic relief. The procedure was tolerated well and both electrodes remained in place without any adverse events. Implications In view of the very limited options currently available to manage CRPS, WPNS can be a promising therapeutic modality.

Comparison of Median Nerve Mechanosensitivity and Pressure Pain Threshold in Patients With Nonspecific Neck Pain and Asymptomatic Individuals.

OBJECTIVE: The purpose of this study was to investigate the presence of median nerve mechanosensitivity by comparing median nerve neurodynamic test results of patients with nonspecific neck pain (NNP) and asymptomatic individuals. METHODS: A total of 40 patients (30 women, 10 men) with NNP between the ages of 21 and 62 years (39.53 ± 10.18 years) and 38 asymptomatic individuals (23 women, 15 men) between the ages of 18 and 60 years (37.13 ± 9.64 years) participated in the study. Pressure pain threshold was assessed with digital pressure algometer, cervical joint range of motion was assessed with a universal goniometer, and median nerve mechanosensitivity was assessed with Upper Limb Neurodynamic Test 1 (ULNT1). The test step where the first sensory response was given, the location and character of the sensory response, and the final elbow extension angle were recorded during ULNT1. RESULTS: Patients with NNP had significantly decreased pressure pain threshold (P < .001), decreased range of motion of cervical flexion (P < .001), and decreased cervical lateral flexion (P = .001) compared with asymptomatic individuals, whereas no change was identified in range of motion of rotation (P = .100). In ULNT1, 45% of patients with NNP reported pain and 40% of them reported stretch. A total of 65% of asymptomatic individuals reported stretch, and 13% of them reported pain. It was identified in ULNT1 that final elbow extension angle was lower in the NNP group compared with asymptomatic individuals (P = .008). CONCLUSION: Median nerve mechanosensitivity increased, pressure pain threshold decreased, and active neck motion was limited in individuals with NNP compared with asymptomatic individuals.

Radial nerve injury following dry needling.

A 27-year-old secretary presented to an orthopaedic outpatients department with a 1-month history of left wrist drop following dry needling. On insertion of a needle, she reported spasms in her left hand followed by a wrist drop. An MRI scan was normal. Electromyogram and nerve conduction studies showed a neuropraxia of the left radial nerve. She was referred to a hand therapist for splinting and intensive hand therapy; however, her symptoms remain unchanged.

Common Synaptic Input to Motor Neurons and Neural Drive to Targeted Reinnervated Muscles.

We compared the behavior of motor neurons innervating their physiological muscle targets with motor neurons from the same spinal segment whose axons were surgically redirected to remnant muscles (targeted muscle reinnervation). The objective was to assess whether motor neurons with nonphysiological innervation receive similar synaptic input and could be voluntary controlled as motor neurons with natural innervation. For this purpose, we acquired high-density EMG signals from the biceps brachii in 5 male transhumeral amputees who underwent targeted reinnervation of this muscle by the ulnar nerve and from the first dorsal interosseous muscle of 5 healthy individuals to investigate the natural innervation of the ulnar nerve. The same recordings were also performed from the biceps brachii muscle of additional 5 able-bodied individuals. The EMG signals were decomposed into discharges of motor unit action potentials. Motor neurons were progressively recruited for the full range of submaximal muscle activation in all conditions. Moreover, their discharge rate significantly increased from recruitment to target activation level in a similar way across the subject groups. Motor neurons across all subject groups received common synaptic input as identified by coherence analysis of their spike trains. However, the relative strength of common input in both the delta (0.5-5 Hz) and alpha (5-13 Hz) bands was significantly smaller for the surgically reinnervated motor neuron pool with respect to the corresponding physiologically innervated one. The results support the novel approach of motor neuron interfacing for prosthesis control and provide new insights into the role of afferent input on motor neuron activity.SIGNIFICANCE STATEMENT Targeted muscle reinnervation surgically redirects nerves that lost their target in the amputation into redundant muscles in the region of the stump. The study of the behavior of motor neurons following this surgery is needed for designing biologically inspired prosthetic control strategies. Moreover, targeted muscle reinnervation offers a human experimental framework for studying the control and behavior of motor neurons when changing their target innervated muscle fibers and sensory feedback. Here, we show that the control of motor neurons and their synaptic input, following reinnervation, was remarkably similar to that of the physiological innervation, although with reduced common drive at some frequencies. The results advance our knowledge on the role of sensory input in the generation of the neural drive to muscles and provide the basis for designing physiologically inspired methods for prosthesis control.

Inhibition of Parkinsonian tremor with cutaneous afferent evoked by transcutaneous electrical nerve stimulation.

BACKGROUND: Recent study suggests that tremor signals are transmitted by way of multi-synaptic corticospinal pathway. Neurophysiological studies have also demonstrated that cutaneous afferents exert potent inhibition to descending motor commands by way of spinal interneurons. We hypothesize in this study that cutaneous afferents could also affect the transmission of tremor signals, thus, inhibit tremor in patients with PD. METHODS: We tested this hypothesis by activating cutaneous afferents in the dorsal hand skin innervated by superficial radial nerve using transcutaneous electrical nerve stimulation (TENS). Eight patients with PD having tremor dominant symptom were recruited to participate in this study using a consistent experimental protocol for tremor inhibition. Resting tremor and electromyogram (EMG) of muscles in the upper extremity of these subjects with PD were recorded, while surface stimulation was applied to the dorsal skin of the hand. Fifteen seconds of data were recorded for 5 s prior to, during and post stimulation. Power spectrum densities (PSDs) of tremor and EMG signals were computed for each data segment. The peak values of PSDs in three data segments were compared to detect evidence of tremor inhibition. RESULTS: At stimulation intensity from 1.5 to 1.75 times of radiating sensation threshold, apparent suppressions of tremor at wrist, forearm and upper arm and in the EMGs were observed immediately at the onset of stimulation. After termination of stimulation, tremor and rhythmic EMG bursts reemerged gradually. Statistical analysis of peak spectral amplitudes showed a significant difference in joint tremors and EMGs during and prior to stimulation in all 8 subjects with PD. The average percentage of suppression was 61.56% in tremor across all joints of all subjects, and 47.97% in EMG of all muscles. The suppression appeared to occur mainly in distal joints and muscles. There was a slight, but inconsistent effect on tremor frequency in the 8 patients with PD tested. CONCLUSIONS: Our results provide direct evidence that tremor in the upper extremity of patients with PD can be inhibited to a large extent with evoked cutaneous reflexes via surface stimulation of the dorsal hand skin area innervated by the superficial radial nerve.