Muscle Stretch Reflexes Research Articles

Neural pathways associated with reduced rigidity during pallidal deep brain stimulation for Parkinson's disease.

Deep brain stimulation (DBS) of the internal segment of the globus pallidus (GPi) can markedly reduce muscle rigidity in people with Parkinson's disease (PD); however, the mechanisms mediating this effect are poorly understood. Computational modeling of DBS provides a method to estimate the relative contributions of neural pathway activations to changes in outcomes. In this study, we generated subject-specific biophysical models of GPi DBS (derived from individual 7-T MRI), including pallidal efferent, putamenal efferent, and internal capsule pathways, to investigate how activation of neural pathways contributed to changes in forearm rigidity in PD. Ten individuals (17 arms) were tested off medication under four conditions: off stimulation, on clinically optimized stimulation, and on stimulation specifically targeting the dorsal GPi or ventral GPi. Quantitative measures of forearm rigidity, with and without a contralateral activation maneuver, were obtained with a robotic manipulandum. Clinically optimized GPi DBS settings significantly reduced forearm rigidity (P < 0.001), which aligned with GPi efferent fiber activation. The model demonstrated that GPi efferent axons could be activated at any location along the GPi dorsal-ventral axis. These results provide evidence that rigidity reduction produced by GPi DBS is mediated by preferential activation of GPi efferents to the thalamus, likely leading to a reduction in excitability of the muscle stretch reflex via overdriving pallidofugal output.NEW & NOTEWORTHY Subject-specific computational models of pallidal deep brain stimulation, in conjunction with quantitative measures of forearm rigidity, were used to examine the neural pathways mediating stimulation-induced changes in rigidity in people with Parkinson's disease. The model uniquely included internal, efferent and adjacent pathways of the basal ganglia. The results demonstrate that reductions in rigidity evoked by deep brain stimulation were principally mediated by the activation of globus pallidus internus efferent pathways.

Musculoskeletal mimics of lumbosacral radiculopathy.

Electrodiagnostic evaluations are commonly requested for patients with suspected radiculopathy. Understanding lower extremity musculoskeletal conditions is essential for electrodiagnostic medicine specialists, as musculoskeletal disorders often mimic or coexist with radiculopathy. This review delineates radicular pain from other types originating from the lumbosacral spine and describes musculoskeletal conditions frequently mimicking radiculopathy, such as those that cause radiating pain and sensorimotor dysfunction. In clinical evaluation, a history of pain radiating along a specific dermatomal territory with associated sensory disturbance suggests radiculopathy. Physical examination findings consistent with radiculopathy include myotomal weakness, depressed or absent muscle stretch reflexes, focal atrophy along a discrete nerve root territory, and potentially positive dural tension maneuvers like the straight leg raise. However, electrodiagnostic medicine specialists must be knowledgeable of musculoskeletal mimics, which may manifest as incomplete radiation within or beyond a dermatomal territory, non-radiating pain, tenderness, and give-way weakness, in the context of a normal neurological examination. A systematic approach to musculoskeletal examination is vital, and this review focuses on high-yield physical examination maneuvers and diagnostic investigations to differentiate between musculoskeletal conditions and radiculopathy. This approach ensures accurate diagnoses, promotes resource stewardship, enhances patient satisfaction, and optimizes care delivery. Musculoskeletal conditions resembling L1 to S4 radiculopathy are reviewed, emphasizing their distinctive features in history, physical examination, and diagnostic investigation. Among the more than 30 musculoskeletal disorders reviewed are hip and knee osteoarthritis, lumbar facet syndrome, myofascial pain syndrome, greater trochanteric pain syndrome, and plantar fasciitis.

Implementation of surface mechanomyography as a novel approach for objective evaluation of phasic muscle stretch reflexes in people with type 2 diabetes

IntroductionDiabetic peripheral neuropathy is the most common complication of diabetes producing metabolic disruptions in the peripheral nervous system. Alteration in the predictable nature of tendon reflexes is the most common indicator suggesting the possibility of diabetic neuropathy. Evaluation of tendon reflexes is a part of various clinical scoring systems that assess neuropathy. The conventional reflex grading scales are subjective, lack temporal data, and have high inter-rater variability. Hence, an indigenous quantification tool was developed to evaluate the tendon reflexes in order to assess diabetic peripheral neuropathy. Materials and methodsA cross-sectional study was carried out in 140 healthy volunteers and 140 patients with type 2 diabetes. The mean age of controls and diabetics (49.1 ± 8.9, 50.7 ± 7.5) years, weight (66.9 ± 9.4, 69.8 ± 11.5) kilograms and BMI (24.5 ± 3.8, 26.1 ± 4.7), respectively. All of them are subjected to evaluation of tendon reflexes using the reflex quantification tool comprised of surface mechanomyography and electrogoniometry that can provide various static and dynamic variables of tendon reflex. ResultsThe dynamic variables such as reflex amplitude, muscle velocity and angular velocity were significantly low in diabetic patients (p: <0.001) whereas latency and duration (p: <0.001) were prolonged. Furthermore, no significant difference was observed in the application of tendon striking force (p: 0.934) among the participants. ConclusionThe current study demonstrates that the proposed reflex quantification tool provides several dynamic variables of patellar tendon reflex, which are significantly affected and altered in diabetic patients suggesting the involvement of peripheral neurons.

Limb spasticity and telemedicine consultation for reconstructive surgery: patient perspectives of surgical assessment.

Spasticity is characterized by increased muscle tone and stretch reflexes, often caused by an upper motor neuron (UMN) syndrome. Many patients live with their dysfunction of their upper or lower limbs for many years and are managed by a multidisciplinary team including physical medicine and rehabilitation specialists, neurologists, and/or physical therapists in an attempt to decrease their spasticity and enhance their quality of life. Reconstructive surgery is a treatment option for many patients living with spasticity. The goal of surgery is to permanently decrease their spastic tone and improve their quality of life. Spastic hemiplegia or hemiparesis is an area of orthopedic surgery that is uniquely suited to telemedicine evaluation. Telemedicine visits can lower the threshold for patients to obtain consultation, receive second opinions, and determine whether traveling for an in-person assessment might be worthwhile, particular to larger medical centers. The objective of our study was to characterize patient perceptions of telemedicine consultation for spasticity surgery and to determine its effectiveness for indicating reconstructive procedures. An electronic survey consisting of 16 questions was distributed to all patients after the virtual consultation from April 2020 to September 2022 as part of a neuro-orthopedic evaluation. Domains of inquiry included patient demographic and diagnosis information, satisfaction with provider assessment, ease of use, appointment preference, and whether surgery was eventually performed. Identifying information was voluntarily provided by patients and allowed for survey data to be linked to the medical record. Patients were included in the study if they were diagnosed with upper and/or lower extremity spasticity, were evaluated by telemedicine visit, and were over the age of 18. They were excluded from the study if they were evaluated for any condition aside from spasticity or returned an incomplete survey. Patients who completed the survey were prospectively followed through December 2022 to determine whether a subsequent in-person visit was pursued and/or reconstructive surgery was performed. A total of 19 of 36 patients completed surveys, for a response rate of 52.7 %. Nearly all (94.7 %, n=18) patients felt that the provider expressed maximal concern for patient questions/worries, included them in decisions regarding care, and appropriately discussed treatment strategies. Similarly, the majority (89.5 %, n=17) were maximally satisfied with explanations about their condition and would recommend the care provider to others. Most patients (84.2 %, n=16) also felt that the ease of communication via the virtual platform was very good. All patients were eventually indicated for and subsequently underwent reconstructive surgery for spasticity. Spasticity patients were overwhelmingly satisfied with their initial virtual consultation as an alternative to face-to-face visits. Telemedicine provides a clinical opportunity for seeking information about spasticity surgery and offers a cost-effective and convenient option for patients who find travel to specialty centers prohibitive.

¿Guillain Barre syndrome and inadequate secretion of antidiuretic hormone, is their relationship possible?

Guillain-Barré syndrome (GBS) is a polyradiculoneuropathy of acute onset and the most common cause of acute flaccid paralysis. It is characterized by the appearance of sensory and/or motor symptoms, accompanied by a decrease or absence of muscle stretch reflexes and other symptoms such as facial paralysis, altered eye movements, bulbar symptoms, altered wakefulness, dysautonomia and ataxia. On the other hand, hydroelectrolyte disorders are associated with serious neurological diseases as a poor prognostic factor; the most affected electrolyte is sodium; in fact, hyponatremia is the most common disorder in hospitalized patients, regardless of the cause; in GBS, it is a frequent finding on admission. It is important to recognize hyponatremia, due to its high morbidity and mortality; it is also a marker of an underlying disease. Syndrome of inappropriate secretion of antidiuretic hormone (SSIADH) is the most common cause of hyponatremia and has been associated with Guillain Barre syndrome; in this way, its diagnosis is a challenge for the doctor; finally, below we describe details of a 70-year-old male patient who was admitted to the intensive care unit, with hyponatremia with a SSIHAD, with good subsequent evolution.

Initial validation of the Mass. General Neuropathy Exam Tool (MAGNET) for evaluation of distal small-fiber neuropathy.

Diagnosis of small-fiber neuropathy (SFN) is hampered by its subjective symptoms and signs. Confirmatory testing is insufficiently available and expensive, so predictive examinations have value. However, few support the 2020 SFN consensus-case-definition requirements or were validated for non-diabetes neuropathies. Thus we developed the Massachusetts General Hospital Neuropathy Exam Tool (MAGNET) and measured diagnostic performance in 160 symptomatic patients evaluated for length-dependent SFN from any cause and 37 healthy volunteers. We compared prevalences of abnormalities (vital signs, pupil responses, lower-limb appearance, pin, light touch, vibration and position sensitivity, great-toe strength, muscle stretch reflexes), and validated diagnostic performance against objective SFN tests: lower-leg skin-biopsy epidermal neurite densities and autonomic function testing (AFT). Sensitivity/specificity, feasibility, test-retest and inter-rater reliability, and convergence with the Utah Early Neuropathy Scale were calculated. Patients' ages averaged 48.5 ± 14.7 years and 70.6% were female. Causes of neuropathy varied, remaining unknown in 59.5%. Among the 46 with abnormal skin biopsies, the most prevalent abnormality was reduced pin sharpness at the toes (71.7%). Inter-rater reliability, test-retest reliability, and convergent validity excelled (range = 91.3-95.6%). Receiver operating characteristics comparing all symptomatic patients versus healthy controls indicated that a MAGNET threshold score of 14 maximized predictive accuracy for skin biopsies (0.74) and a 30 cut-off maximized accuracy for predicting AFT (0.60). Analyzing patients with any abnormal neuropathy-test results identified areas-under-the-curves of 0.87-0.89 for predicting a diagnostic result, accuracy = 0.80-0.89, and Youden's index = 0.62. Overall, MAGNET was 80%-85% accurate for stratifying patients with abnormal versus normal neuropathy test results. MAGNET quickly generates research-quality metrics during clinical examinations.

Cancer survivors post-chemotherapy exhibit unimpaired short-latency stretch reflexes in the proximal upper extremity.

Oxaliplatin (OX) chemotherapy can lead to long-term sensorimotor impairments in cancer survivors. The impairments are often thought to be caused by OX-induced progressive degeneration of sensory afferents known as length-dependent dying-back sensory neuropathy. However, recent preclinical work has identified functional defects in the encoding of muscle proprioceptors and in motoneuron firing. These functional defects in the proprioceptive sensorimotor circuitry could readily impair muscle stretch reflexes, a fundamental building block of motor coordination. Given that muscle proprioceptors are distributed throughout skeletal muscle, defects in stretch reflexes could be widespread, including in the proximal region where dying-back sensory neuropathy is less prominent. All previous investigations on chemotherapy-related reflex changes focused on distal joints, leading to results that could be influenced by dying-back sensory neuropathy rather than more specific changes to sensorimotor circuitry. Our study extends this earlier work by quantifying stretch reflexes in the shoulder muscles in 16 cancer survivors and 16 healthy controls. Conduction studies of the sensory nerves in hand were completed to detect distal sensory neuropathy. We found no significant differences in the short-latency stretch reflexes (amplitude and latency) of the shoulder muscles between cancer survivors and healthy controls, contrasting with the expected differences based on the preclinical work. Our results may be linked to differences between the human and preclinical testing paradigms including, among many possibilities, differences in the tested limb or species. Determining the source of these differences will be important for developing a complete picture of how OX chemotherapy contributes to long-term sensorimotor impairments.NEW & NOTEWORTHY Our results showed that cancer survivors after oxaliplatin (OX) treatment exhibited stretch reflexes that were comparable with age-matched healthy individuals in the proximal upper limb. The lack of OX effect might be linked to differences between the clinical and preclinical testing paradigms. These findings refine our expectations derived from the preclinical study and guide future assessments of OX effects that may have been insensitive to our measurement techniques.

A General Approach for the Modelling of Negative Feedback Physiological Control Systems.

Mathematical models can improve the understanding of physiological systems behaviour, which is a fundamental topic in the bioengineering field. Having a reliable model enables researchers to carry out in silico experiments, which require less time and resources compared to their in vivo and in vitro counterparts. This work's objective is to capture the characteristics that a nonlinear dynamical mathematical model should exhibit, in order to describe physiological control systems at different scales. The similarities among various negative feedback physiological systems have been investigated and a unique general framework to describe them has been proposed. Within such a framework, both the existence and stability of equilibrium points are investigated. The model here introduced is based on a closed-loop topology, on which the homeostatic process is based. Finally, to validate the model, three paradigmatic examples of physiological control systems are illustrated and discussed: the ultrasensitivity mechanism for achieving homeostasis in biomolecular circuits, the blood glucose regulation, and the neuromuscular reflex arc (also referred to as muscle stretch reflex). The results show that, by a suitable choice of the modelling functions, the dynamic evolution of the systems under study can be described through the proposed general nonlinear model. Furthermore, the analysis of the equilibrium points and dynamics of the above-mentioned systems are consistent with the literature.

MRI negative Varicella zoster virus (VZV) plexopathy in a young man with history of malignancy (P2-4.001)

<h3>Objective:</h3> To emphasize the importance of including VZV plexopathy in differential diagnosis in young individuals and to prevent the delay in diagnosis and treatment <h3>Background:</h3> VZV-associated plexopathy in mainly patients over 60 years old. Post herpetic neuralgia is a well-known complication of Herpes Zoster (HZ), however segmental zoster paresis secondary to HZ was reported in 1–20% of the cases in literature. MRI findings may be positive in up to 70% of the patients. <h3>Design/Methods:</h3> N/A <h3>Results:</h3> 43 years-old man with history of grade 2 left frontal oligodendroglioma which was treated with 2 partial resections, radiation and adjuvant procarbazine/lomustine presented with left upper extremity pain and developed a blistering rash in dermatomal pattern in left proximal upper extremity 2 weeks after the initial symptoms. He was diagnosed with shingles and treated with steroids and acyclovir with minimal improvement. 6 weeks after presentation, physical exam revealed left deltoid, supraspinatus and infraspinatus weakness with normal muscle stretch reflexes and decreased sensation on C5 dermatome. EMG revealed absent left lateral antebrachial cutaneous sensory nerve action potentials (SNAP) amplitude, and a small left radial SNAP amplitude compared to the right side. Evidence of ongoing denervation with reinnervation was seen in the left upper trunk supplied muscles. MRI of the brachial plexus was negative for any abnormalities. Patient was diagnosed with VZV-associated plexopathy, improved with pregabalin and physical therapy. <h3>Conclusions:</h3> Our patient was significantly younger than expected in HZ group. MRI usually shows T2 hyperintensities and thickening of the nerve roots in patients with VZV-associated plexopathy. However, the presentation, onset of symptoms, characteristics of the rash and clinical course was diagnostic of HZ, and the weakness pattern, supported by the EMG findings were diagnostic for VZV-associated plexopathy. <b>Disclosure:</b> Dr. Gul has nothing to disclose. Ms. Ahmed has nothing to disclose. Dr. McGraw has nothing to disclose. Dr. Alshiekh Nasany has nothing to disclose.

Visual feedback-dependent modulation of arousal, postural control, and muscle stretch reflexes assessed in real and virtual environments.

The mechanisms regulating neuromuscular control of standing balance can be influenced by visual sensory feedback and arousal. Virtual reality (VR) is a cutting-edge tool for probing the neural control of balance and its dependence on visual feedback, but whether VR induces neuromodulation akin to that seen in real environments (eyes open vs. closed or ground level vs. height platform) remains unclear. Here we monitored 20 healthy young adults (mean age 23.3 ± 3.2 years; 10 females) during four conditions of quiet standing. Two real world conditions (eyes open and eyes closed; REO and REC) preceded two eyes-open virtual 'low' (ground level; VRL) and 'high' (14 m height platform; VRH) conditions. We measured arousal via electrodermal activity and psychosocial questionnaires rating perceived fear and anxiety. We recorded surface electromyography over the right soleus, medial gastrocnemius, and tibialis anterior, and performed force plate posturography. As a proxy for modulations in neural control, we assessed lower limb reflexive muscle responses evoked by tendon vibration and electrical stimulation. Physiological and perceptual indicators of fear and anxiety increased in the VRH condition. Background soleus muscle activation was not different across conditions; however, significant increases in muscle activity were observed for medial gastrocnemius and tibialis anterior in VRH relative to REO. The mean power frequency of postural sway also increased in the VRH condition relative to REO. Finally, with a fixed stimulus level across conditions, mechanically evoked reflexes remained constant, while H-reflex amplitudes decreased in strength within virtual reality. Notably, H-reflexes were lower in the VRL condition than REO, suggesting that these ostensibly similar visual environments produce different states of reflexive balance control. In summary, we provide novel evidence that VR can be used to modulate upright postural control, but caution that standing balance in analogous real and virtual environments may involve different neural control states.

Assessing shoulder muscle stretch reflexes following breast cancer treatment and postmastectomy breast reconstruction.

Muscle stiffness is altered following postmastectomy breast reconstruction and breast cancer treatment. The exact mechanisms underlying these alterations are unknown; however, muscle stretch reflexes may play a role. This work examined short- (SLR) and long-latency (LLR) shoulder muscle stretch reflexes in breast cancer survivors. Forty-nine patients who had undergone postmastectomy breast reconstruction, 17 who had undergone chemoradiation, and 18 healthy, age-matched controls were enrolled. Muscle activity was recorded from the clavicular and sternocostal regions of the pectoralis major and anterior, middle, and posterior deltoids during vertical ab/adduction or horizontal flex/extension perturbations while participants maintained minimal torques. SLR and LLR were quantified for each muscle. Our major finding was that following postmastectomy breast reconstruction, SLR and LLR are impaired in the clavicular region of the pectoralis major. Individuals who had chemoradiation had impaired stretch reflexes in the clavicular and sternocostal region of the pectoralis major, anterior, middle, and posterior deltoid. These findings indicate that breast cancer treatments alter the regulation of shoulder muscle stretch reflexes and may be associated with surgical or nonsurgical damage to the pectoral fascia, muscle spindles, and/or sensory Ia afferents.NEW & NOTEWORTHY Shoulder muscle stretch reflexes may be impacted following postmastectomy breast reconstruction and chemoradiation. Here, we examined short- and long-latency shoulder muscle stretch reflexes in two experiments following common breast reconstruction procedures and chemoradiation. We show impairments in pectoralis major stretch reflexes following postmastectomy breast reconstruction and pectoralis major and deltoid muscle stretch reflexes following chemoradiation. These findings indicate that breast cancer treatments alter the regulation of shoulder muscle stretch reflexes.

Electrophysiological Evaluation of a Patient With Chronic Erb-Duchenne Palsy (C5-C6): A Case Study

Background Erb-Duchenne palsy describes injury to the upper trunk of the brachial plexus or the C5 and C6 nerve roots. It typically occurs from a traction injury that increases the angle between the head and shoulder girdle, placing excessive strain on the cervical nerve roots and brachial plexus. Injury to the C5 and C6 nerve roots and/or upper trunk of the brachial plexus results in severe shoulder girdle weakness with preservation of the hand intrinsic muscles and some forearm motions. 2 , 9 Case Presentation A 64-year-old right-hand–dominant male was referred by his orthopaedic surgeon for electromyograhy (EMG) and nerve conduction studies (NCS) to evaluate the nerve and muscle structures in the right upper extremity prior to surgical fusion of the glenohumeral joint for chronic humeral head subluxation and shoulder instability. The patient was diagnosed with a right Erb-Duchenne palsy following a hit-and-run motor vehicle accident in 2001. Physical examination revealed muscle weakness in all muscles representative of the right C5-C6 myotomes and absent biceps brachii and brachioradialis muscle stretch reflexes. Outcome and Follow Up The clinical exam findings and electrophysiological testing evidence suggested that the patient had a chronic right C5-C6 radiculopathy affecting the right upper extremity and the right mid cervical paravertebral muscles, consistent with the referring diagnosis of Erb-Duchenne palsy. Needle EMG findings suggested little chance of further neurological recovery, so the patient underwent a right glenohumeral joint fusion to improve the stability of the right shoulder and limit glenohumeral subluxation. Discussion This case study highlights the role of a thorough neuromusculoskeletal exam in the differential diagnostic process for a patient with a right C5-C6 Erb-Duchenne palsy, and the role of EMG and NCS in distinguishing brachial plexopathy from cervical radiculopathy. Additionally, EMG and NCS provided prognostic information on potential neurological recovery, suggesting that surgical fusion was the best intervention. JOSPT Cases 2022;2(3):152–158. Epub: 21 June 2022. doi:10.2519/josptcases.2022.11174

Functional assessment of stretch hyperreflexia in children with cerebral palsy using treadmill perturbations

BackgroundAs hyperactive muscle stretch reflexes hinder movement in patients with central nervous system disorders, they are a common target of treatment. To improve treatment evaluation, hyperactive reflexes should be assessed during activities as walking rather than passively. This study systematically explores the feasibility, reliability and validity of sudden treadmill perturbations to evoke and quantify calf muscle stretch reflexes during walking in children with neurological disorders.MethodsWe performed an observational cross-sectional study including 24 children with cerebral palsy (CP; 6–16 years) and 14 typically developing children (TD; 6–15 years). Short belt accelerations were applied at three different intensities while children walked at comfortable speed. Lower leg kinematics, musculo-tendon lengthening and velocity, muscle activity and spatiotemporal parameters were measured to analyze perturbation responses.ResultsWe first demonstrated protocol feasibility: the protocol was completed by all but three children who ceased participation due to fatigue. All remaining children were able to maintain their gait pattern during perturbation trials without anticipatory adaptations in ankle kinematics, spatiotemporal parameters and muscle activity. Second, we showed the protocol’s reliability: there was no systematic change in muscle response over time (P = 0.21–0.54) and a bootstrapping procedure indicated sufficient number of perturbations, as the last perturbation repetition only reduced variability by ~ 2%. Third, we evaluated construct validity by showing that responses comply with neurophysiological criteria for stretch reflexes: perturbations superimposed calf muscle lengthening (P < 0.001 for both CP and TD) in all but one participant. This elicited increased calf muscle activity (359 ± 190% for CP and 231 ± 68% for TD, both P < 0.001) in the gastrocnemius medialis muscle, which increased with perturbation intensity (P < 0.001), according to the velocity-dependent nature of stretch reflexes. Finally, construct validity was shown from a clinical perspective: stretch reflexes were 1.7 times higher for CP than TD for the gastrocnemius medialis muscle (P = 0.017).ConclusionsThe feasibility and reliability of the protocol, as well as the construct validity—shown by the exaggerated velocity-dependent nature of the measured responses—strongly support the use of treadmill perturbations to quantify stretch hyperreflexia during gait. We therefore provided a framework which can be used to inform clinical decision making and treatment evaluation.

Similar stretch reflexes and behavioral patterns are expressed by the dominant and nondominant arms during postural control.

Limb dominance is evident in many daily activities, leading to the prominent idea that each hemisphere of the brain specializes in controlling different aspects of movement. Past studies suggest that the dominant arm is primarily controlled via an internal model of limb dynamics that enables the nervous system to produce efficient movements. In contrast, the nondominant arm may be primarily controlled via impedance mechanisms that rely on the strong modulation of sensory feedback from individual joints to control limb posture. We tested whether such differences are evident in behavioral responses and stretch reflexes following sudden displacement of the arm during posture control. Experiment 1 applied specific combinations of elbow-shoulder torque perturbations (the same for all participants). Peak joint displacements, return times, end point accuracy, and the directional tuning and amplitude of stretch reflexes in nearly all muscles were not statistically different between the two arms. Experiment 2 induced specific combinations of joint motion (the same for all participants). Again, peak joint displacements, return times, end point accuracy, and the directional tuning and amplitude of stretch reflexes in nearly all muscles did not differ statistically when countering the imposed loads with each arm. Moderate to strong correlations were found between stretch reflexes and behavioral responses to the perturbations with the two arms across both experiments. Collectively, the results do not support the idea that the dominant arm specializes in exploiting internal models and the nondominant arm in impedance control by increasing reflex gains to counter sudden loads imposed on the arms during posture control.NEW & NOTEWORTHY A prominent hypothesis is that the nervous system controls the dominant arm through predictive internal models and the nondominant arm through impedance mechanisms. We tested whether stretch reflexes of muscles in the two arms also display such specialization during posture control. Nearly all behavioral responses and stretch reflexes did not differ statistically but were strongly correlated between the arms. The results indicate individual signatures of feedback control that are common for the two arms.

SY2.3. Evaluation of dystonia

Dystonia is a syndrome characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both. It can be primary or secondary and the patient can present with pure dystonia or dystonia along with other movement disorders such as tremor, myoclonus, parkinsonism, etc. Evaluation of a patient presenting primarily with dystonia includes detailed clinical evaluation, haematologic and neurometabolic work up, imaging and neurophysiological/ electrophysiological studies. This presentation will focus on the electrophysiological evaluation of dystonia, which helps in understanding the pathophysiology and better characterization of the abnormal movement. Compared to tremor and myoclonus, electrophysiological evaluation of muscle spasms and dystonia is difficult. The first step is recording surface EMG from the involved muscles for prolonged periods during abnormal movements (dystonia), rest, and with voluntary contraction. The agonists and antagonists should be included to detect co-contraction, and the unaffected muscles of the same or opposite limbs should also be studied to document overflow dystonia if present. During EMG evaluation, patients are also asked to perform various tasks which can induce dystonia, such as mental arithmetic, finger tapping and opening and closing fist of the unaffected hand, writing (in patients with writer’s cramp). EMG is analyzed to determine: (i) the pattern of EMG activity in agonists and antagonists during dystonia (spasm) (ii) duration of each EMG burst (iii) the regularity of occurrence of EMG bursts, (iv) presence of overflow activity in remote muscles while performing discrete voluntary acts, and (v) the difference in the degree of EMG activity (area of rectified EMG) between epochs with and without muscle spasms. Other investigations which are often useful to characterize dystonia or a dystonic syndrome include: (i) H-reflex recovery curve (ii) mechanically and electrically induced long-latency muscle stretch reflex (iii) reciprocal inhibition between antagonistic muscles (iv) brainstem reflexes such as blink reflex (v) cortical SEP (vi) Bereitschaftpotential (BP) and Contingent negative variation (CNV) and (viii) transcranial magnetic stimulation (TMS). TMS specifically helps to study the excitatory and inhibitory changes in the brain in patients with dystonia and may also be a useful tool to monitor therapeutic interventions.

Symposium 4: Neuromuscular junction and related disorders SY4.1. Myasthenia gravis and related disorders

Autoimmune myasthenia gravis (MG) results from autoantibodies that bind to the neuromuscular junction (NMJ). Incidence and prevalence vary worldwide; the estimated US prevalence is 20/100,000, or ∼60,000 patients. Women develop MG more often before age 40, men after 50. Drooping eyelids or double vision is the first symptom in 60%; weakness remains limited to periocular muscles in 10–15% – ocular myasthenia. The voice may be nasal or hoarse, especially after prolonged talking, and swallowed liquids may escape through the nose. Weakness typically worsens throughout the day. Spontaneous improvement may occur early on but is rarely permanent. The diagnosis depends on recognizing distinctive patterns of weakness and confirmation by serologic and electrodiagnostic tests. 80–85% of patients have circulating anti-AChR antibodies; repetitive nerve stimulation (RNS) demonstrates abnormal neuromuscular transmission (NMT) in up to 90% of generalized MG and 60% of ocular myasthenia. Increased jitter is found in almost all patients if appropriate muscles are examined. Approximately 10% of patients have antibodies to muscle specific tyrosine kinase (MuSK). Clinical findings resemble non-MuSK MG in some patients; many have predominant weakness in cranio-bulbar muscles with marked atrophy. Others have predominant neck, shoulder and respiratory weakness. With selected treatment most non-MuSK and MuSK-MG patients have only minimal long-term morbidity. Congenital myasthenic syndromes result from genetic defects of muscle endplate molecules involved in NMT; most have autosomal recessive inheritance. The diagnosis is suggested by clinical features and response to cholinesterase inhibitors, or electrodiagnostic findings. Identification of specific genetic or physiologic defects requires genetic studies or specialized morphological and electrophysiological studies. Lambert-Eaton myasthenia results from antibodies to voltage-gated calcium channels (VGCC) on presynaptic nerve terminals, which produces the classic triad of weakness, reduced muscle stretch reflexes and autonomic dysfunction. Approximately 50% have an underlying malignancy, usually small cell lung cancer. The diagnosis is confirmed by a decrementing pattern during low frequency RNS and low muscle responses that increase at least 60% after muscle activation. Antibodies to the VGCC are found in most cases. Treatment is initially directed against any underlying malignancy. Amifampridine produces symptomatic improvement in most patients; immunomodulatory therapy may provide modest benefit in some.

Optically pumped magnetometers reveal fasciculations non-invasively

ObjectiveThis proof-of-principle-study evaluated the extent to which spontaneous activity (SA) of the muscle can be detected via non-invasive magnetomyography (MMG) with optically pumped magnetometers (OPM). MethodsFive patients, who together exhibited all forms of SA (fibrillations, positive sharp waves, fasciculations, myotonic discharges, complex-repetitive discharges) with conventional needle electromyography (EMG), were studied by OPM-MMG and simultaneous surface EMG (sEMG) while at rest, during light muscle activation, and when a muscle stretch reflex was elicited. Three healthy subjects were measured as controls. SA was considered apparent in the OPM-MMG if a signal could be visually detected that corresponded in shape and frequency to the SA in the respective needle EMG. ResultsSA in the context of fasciculations could be detected in 2 of 5 patients by simultaneous OPM-MMG/sEMG. Other forms of SA could not be detected at rest, during light muscle activation, or after provocation of a muscle stretch reflex. ConclusionsResults show that fasciculations could be detected non-invasively via a new method (OPM). SignificanceWe show that other forms of SA are not detectable with current OPM and propose necessary technical solutions to overcome this circumstance. Our results motivate to pursue OPM-MMG as a new clinical neurophysiological diagnostic.

Possible Mechanisms for the Effects of Sound Vibration on Human Health.

This paper presents a narrative review of research literature to “map the landscape” of the mechanisms of the effect of sound vibration on humans including the physiological, neurological, and biochemical. It begins by narrowing music to sound and sound to vibration. The focus is on low frequency sound (up to 250 Hz) including infrasound (1–16 Hz). Types of application are described and include whole body vibration, vibroacoustics, and focal applications of vibration. Literature on mechanisms of response to vibration is categorized into hemodynamic, neurological, and musculoskeletal. Basic mechanisms of hemodynamic effects including stimulation of endothelial cells and vibropercussion; of neurological effects including protein kinases activation, nerve stimulation with a specific look at vibratory analgesia, and oscillatory coherence; of musculoskeletal effects including muscle stretch reflex, bone cell progenitor fate, vibration effects on bone ossification and resorption, and anabolic effects on spine and intervertebral discs. In every category research on clinical applications are described. The conclusion points to the complexity of the field of vibrational medicine and calls for specific comparative research on type of vibration delivery, amount of body or surface being stimulated, effect of specific frequencies and intensities to specific mechanisms, and to greater interdisciplinary cooperation and focus.

SpES: A new portable device for objective assessment of hypertonia in clinical practice

Spasticity is a motor disorder that affects millions around the world. It is a particular type of hypertonia characterized by the speed-dependent increase of the muscle stretch reflex, where its correct evaluation is essential for rehabilitation. The preferred method for this assessment is the Modified Ashworth Scale (MAS), a rank derived from clinical observations. Currently, few methods can quantify this disorder objectively. Tonic Stretch Reflex Threshold (TSRT) is a parameter speed-dependent obtained from electromyographic (EMG) measurements and angular signals. Therefore, the objective was to develop portable equipment for quantitative assessments of hypertonia based on TSRT. To this end, we designed an instrument composed of single-channel EMG, flexible optical goniometer, and software for the online computing of TSRT from acquired signals. The new equipment named SpES (Spasticity Evaluation System) was applied to measuring hypertonia of the biceps brachii in twenty-two participants. The experiment was performed during manual passive stretching of the affected limb at predefined speeds. The results provided by SpES presented a satisfactory coefficient of determination (0.70) and a strong correlation with MAS (0.79). In summary, while MAS depends on precise clinical observations, SpES has the TSRT quantitative method embedded for reaching an objective assessment of hypertonia in clinical practice.

Clinical Reasoning: A 7-Year-Old Boy With Acute-Onset Altered Mental Status.

A 7-year-old boy presented with acute-onset headache, vomiting, and confusion during summer. Two months previously, he developed right thigh pain, causing intermittent limping. Three days before admission, he developed headache; 1 day later, he experienced fatigue, nausea, and vomiting. On the day of presentation, symptoms included behavioral change (showered 15 times), unsteadiness, and new palmoplantar rash. He presented with confusion and lethargy and was transferred to our facility. His father had a recent gastrointestinal illness, but there were no other sick contacts. There were no recent weight changes, fever, tick/animal exposure, or travel. Past medical history included prior herpes simplex virus (HSV)–positive facial lesion (at 5 years old). The patient took no medications, had no known allergies, was developmentally normal, and was appropriately vaccinated. On general examination, he was somnolent and irritable, and had a palpable right thigh mass and palmar/solar petechiae. Neurologically, he was arousable to light touch, followed only simple midline commands, answered yes/no to orientation questions and responded to all naming questions with “I don't know.” Cranial nerves were intact. He had normal muscle bulk/tone and at least 3/5 strength throughout, but encephalopathy limited assessment. He had normal sensation to light touch and muscle stretch reflexes, neutral plantar responses, and no dysmetria. The patient sat in bed independently but refused to stand or walk.