M/RMS: an EMG method for quantifying upper motoneuron and functional weakness

Spatially selective stimulation of the pig vagus nerve to modulate target effect versus side effect

Electrical stimulation of the cervical vagus nerve using implanted electrodes (VNS) is FDA-approved for the treatment of drug-resistant epilepsy, treatment-resistant depression, and most recently, chronic ischemic stroke rehabilitation. However, VNS is critically limited by the unwanted stimulation of nearby neck muscles-a result of non-specific stimulation activating motor nerve fibers within the vagus. Prior studies suggested that precise placement of small epineural electrodes can modify VNS therapeutic effects, such as cardiac responses. However, it remains unclear if placement can alter the balance between intended effect and limiting side effect. We used an FDA investigational device exemption approved six-contact epineural cuff to deliver VNS in pigs and quantified how epineural electrode location impacts on- and off-target VNS activation. Detailed post-mortem histology was conducted to understand how the underlying neuroanatomy impacts observed functional responses. Here we report the discovery and characterization of clear neuroanatomy-dependent differences in threshold and saturation for responses related to both effect (change in heart rate) and side effect (neck muscle contractions). The histological and electrophysiological data were used to develop and validate subject-specific computation models of VNS, creating a well-grounded quantitative framework to optimize electrode location-specific activation of nerve fibers governing intended effect versus unwanted side effect.

Diagnostic accuracy of clinical signs and investigations for functional weakness, sensory and movement disorders: A systematic review

INTRODUCTION

Patients with functional neurological disorders (FND) present with weakness, sensory or movement disorder without corresponding brain pathology. The current classificatory systems suggest an inclusionary approach to diagnose FND. Hence, there is a need to systematically evaluate the diagnostic accuracy of clinical signs and electrophysiological investigations in view of the lack of gold standard tests to diagnose FND.

METHODS

PubMed and SCOPUS databases were searched for studies published from Jan 1950 to Jan 2022 which reported the diagnostic accuracy of clinical signs and electrophysiological investigations in patients with FND. The Newcastle Ottawa scale was used to assess the quality of the studies.

RESULTS

Twenty-one studies (727 cases and 932 controls), of which 16 reported clinical signs and, five reported electrophysiological investigations, were included in the review. Two studies were of good quality, 17 of moderate quality, and two of poor quality. We identified 46 clinical signs (24 in weakness, 3 in sensory, and 19 in movement disorders) and 17 investigations (all in movement disorders). Specificity values for signs and investigations were comparatively high compared to the wide variance in sensitivity values.

CONCLUSION

Electrophysiological investigations appear to have a promising role in diagnosing FND, particularly functional movement disorders. The combined use of individual clinical signs and electrophysiological investigations may support and improve diagnostic certainty of FND. Future research can focus on improving the methodology and validating the existing clinical signs and electrophysiological investigations to enhance the validity of the composite diagnostic criterias for FND diagnosis.

Electromyographic Evaluation of Temporalis Muscle Following Temporalis Tendon Transfer (Facial Reanimation) Surgery

Facial paralysis is a significant functional and aesthetic handicap. Many techniques have been defined for facial reanimation. The aim of the study was to evaluate postoperative electromyographical (EMG) activity of temporalis muscle to assess the potential neural impairments related to the surgical procedure.

METHODOLOGY

Four patients with facial paralysis were operated with the temporalis muscle tendon transfer technique. Simultaneous surface electromyographic (sEMG) activity at first postoperative year from the bilateral temporalis and masseter muscles was obtained at mandibular rest position and then during maximal clenching.

RESULTS

Patients were followed for a minimum period of 18 months. Surface electromyographic evaluations during passive state revealed similar values for the operated and contralateral side. Measurements during active "clench-smiling" of the jaw revealed similar amplitudes for both muscles of the operated side in all cases except case #2. Case #2 revealed lower values for both measurements of temporalis and masseter muscles of the operated side compared with the contralateral side. Dissonant results of case #2 can be the consequence of impaired temporalis muscle activity because of the tension on the muscle as a consequence of overcorrection.

CONCLUSION

Temporalis muscle transfer to the perioral region does not hinder contractility of the muscle as long as the facial deformity is not overcorrected.

Examination of hand muscle activation and motor unit indices derived from surface EMG in chronic stroke

In this study, we used muscle and motor unit indices, derived from convenient surface electromyography (EMG) measurements, for examination of paretic muscle changes post stroke. For 12 stroke subjects, compound muscle action potential and voluntary surface EMG signals were recorded from paretic and contralateral first dorsal interosseous, abductor pollicis brevis, and abductor digiti minimi muscles. Muscle activation index (AI), motor unit number index (MUNIX), and motor unit size index (MUSIX) were then calculated for each muscle. There was a significant AI reduction for all the three muscles in paretic side compared with contralateral side, providing an evidence of muscle activation deficiency after stroke. The hand MUNIX (defined by summing the values from the three muscles) was significantly reduced in paretic side compared with contralateral side, whereas the hand MUSIX was not significantly different. Furthermore, diverse changes in MUNIX and MUSIX were observed from the three muscles. A major feature of the present examinations is the primary reliance on surface EMG, which offers practical benefits because it is noninvasive, induces minimal discomfort and can be performed quickly.

Interpretation of EMG integral or RMS and estimates of "neuromuscular efficiency" can be misleading in fatiguing contraction

In occupational and sports physiology, reduction of neuromuscular efficiency (NME) and elevation of amplitude characteristics, such as root mean square (RMS) or integral of surface electromyographic (EMG) signals detected during fatiguing submaximal contraction are often related to changes in neural drive. However, there is data showing changes in the EMG integral (I(EMG)) and RMS due to peripheral factors. Causes for these changes are not fully understood. On the basis of computer simulation, we demonstrate that lengthening of intracellular action potential (IAP) profile typical for fatiguing contraction could affect EMG amplitude characteristics stronger than alteration in neural drive (central factors) defined by number of active motor units (MUs) and their firing rates. Thus, relation of these EMG amplitude characteristics only to central mechanisms can be misleading. It was also found that to discriminate between changes in RMS or I(EMG) due to alterations in neural drive from changes due to alterations in peripheral factors it is better to normalize RMS of EMG signals to the RMS of M-wave. In massive muscles, such normalization is more appropriate than normalization to either peak-to-peak amplitude or area of M-wave proposed in literature.

Électromyographie de surface et fonction musculaire en pathologie

Surface electromyography (SEMG) had been and is still widely used in kinesiology and fatigue studies. Its use in routine clinical neurophysiology remains limited. Patients are requiring non-invasive EMG, which could also benefit to physicians and health care system looking for tools to evaluate muscle function in neuromuscular diseases as well as for therapeutic trials. This is the aim of our clinical studies. We apply SEMG envelope signal analysis acquired from maximal voluntary contractions, and the related compound muscle action potential (CMAP). These unspecific parameters cannot be used for neuromuscular diseases diagnosis, objective under study by many research teams. In nerve lesions follow-up studies, our SEMG procedure is related to motor clinical progression. We are currently evaluating it in chronic neuromuscular diseases. The respective contribution in neuromuscular disorders of the different neurophysiology techniques has still to be confirmed, and compared to force measurement by manual or quantitative testing, dynamometry, other suggested techniques (spectroscopy, imaging) as well as functional scales.

Correlation of polyelectromyographic patterns and clinical motor manifestations in children with cerebral palsy

OBJECTIVE

We investigated the correlation between movement patterns, measured by polyelectromyography (PEMG), and clinical motor manifestations in children with cerebral palsy.

DESIGN

Subjects included 53 children with spastic cerebral palsy (diplegic [n = 43] and quadriplegic [n = 10] groups) and 18 normal children. All children underwent PEMG assessments, recorded from pairs of flexor/extensor muscles during voluntary movement. We correlated PEMG patterns with clinical motor assessments, including muscle tone, range of motion, and ambulatory and functional capacities in the children with cerebral palsy.

RESULTS

Children with cerebral palsy exhibited four distinct PEMG patterns, ranging from partial reciprocal to complete synchrony. Lower PEMG pattern scores were significantly associated with better ambulatory (rho = 0.88, P < 0.01) and functional (rho = 0.78, P < 0.01) capacities. PEMG patterns also had weakly positive relationships with muscle tone (rho > 0.33, P < 0.01) and range of motion of both lower limbs (rho > 0.31, P < 0.01). Most children of spastic diplegia with PEMG patterns II and III had independent ambulatory capacities and mild limitation of functional capacity, whereas most children with pattern of IV and V had no ambulatory abilities and no independent functional capacities (P < 0.01).

CONCLUSIONS

These findings suggest that PEMG patterns correlate with clinical motor deficits and may allow us to plan treatment strategies based on underlying motor control in cerebral palsy.

The effect of locomotor training combined with functional electrical stimulation in chronic spinal cord injured subjects: walking and reflex studies

With the new developments in traumatology medicine, the majority of spinal cord injuries sustained are clinically incomplete and the proportion is likely to continue to rise. Thus, it is necessary to continue to develop new treatment and rehabilitation strategies and understand the factors that can enhance recovery of walking following spinal cord injury (SCI). One new development is the use of functional electrical stimulation (FES) device to assist locomotion. The objective of this review is to present findings from some recent studies on the effect of long-term locomotor training with FES in subjects with SCI. Promising results are shown in all outcome measures of walking, such as functional mobility, speed, spatio-temporal parameters, and the physiological cost of walking. Furthermore, the change in the walking behavior could be associated with plasticity in the CNS organization, as seen by the modification of the stretch reflex and changes in the corticospinal projection to muscles of the lower leg. In conclusion, recovery of walking is an increasing possibility for a large number of people with SCI. New modalities of treatment have become available for this population but most still need to be evaluated for their efficacy. This review has focused on FES assisted walking as a therapeutic modality in subjects with chronic SCI, but it is envisaged that the care and recovery of SCI in the early phase of recovery could also be improved.

Correlation of polyelectromyographic patterns and clinical upper motor neuron syndrome in hemiplegic stroke patients

OBJECTIVE

To investigate the correlation between movement patterns, measured by polyelectromyography (PEMG), and clinical upper motor neuron (UMN) syndrome in stroke patients.

DESIGN

PEMG patterns, recorded from pairs of flexor-extensor muscles during voluntary maneuvers, and motor outcomes were assessed approximately 1 month after stroke (early stage). Motor outcomes were reassessed 6 months later (late stage).

PARTICIPANTS

Thirty-nine hemiplegic stroke patients and 18 healthy control subjects.

MAIN OUTCOME MEASURES

Passive stretch reflexes (PSRs), Brunnstrom's stages, and walking ability.

RESULTS

Six PEMG patterns, varying from complete reciprocal to complete synchrony, were identified. Higher PEMG pattern scores were associated with better Brunnstrom's stages (r > .80), walking ability (r > .39), and some PSRs (r < -.37). PEMG patterns could separate patterns 1 and 2 from patterns 3 and 4 for patients with early Brunnstrom's stages 1 and 2. Patterns 1 and 2 (reduced agonist electromyographic activities) indicated weakness and resulted in the worst motor outcomes. Patterns 3 and 4 (cocontraction and coactivation) indicated spasticity and associated synergistic movements. Patients with patterns of 5 and 6 (reciprocal electromyographic activities) had more selective motor control.

CONCLUSIONS

PEMG patterns correlate with clinical UMN syndromes and may allow treatment strategy planning on the basis of underlying motor control, as well as the prediction of final motor outcomes soon after stroke, even in patients who cannot move their legs initially.

Spinal cord infarction: varying degrees of upper and lower motoneuron dysfunction

Five patients with spinal cord infarction underwent electrophysiologic evaluation. Two subjects with complete paralysis had absent compound muscle action potentials (M-responses), suggesting complete loss of lower motoneurons (LMN). Three subjects with incomplete cord infarction had preserved M-responses, reduced voluntary recruitment and abnormally slow motor-unit firing rates during maximal effort, suggesting upper motoneuron (UMN) weakness. These five patients demonstrate a range of neuronal damage after cord ischemia. With severe cord infarction, there is LMN degeneration and paralysis. With partial cord infarction, there is selective interneuron loss, resulting in UMN weakness. Electrodiagnostic evaluation can help determine prognosis for motor recovery after spinal cord infarction.

Vrms/T quantitation: usefulness in patients with neuropathies

This study evaluates the sensitivity of root mean square voltage (Vrms)/turns (T) ratios in neuropathies. Data were recorded with concentric needle electrodes from the biceps brachii, first dorsal interosseous, tibialis anterior, and calf muscles. Recordings were analyzed from 35 normal subjects as well as 24 consecutive patients referred for evaluation of neuropathic disorders. Direct tension measurements were not required. Reasoning from studies in normal subjects in which Vrms/T values were related to measurements of relative tension, the data were recorded during strong muscle contractions of less than 80% of maximum tension as monitored by mean amplitude values. For all 5 muscles, mean Vrms/T values > or = 1.0 calculated from four separate needle sites were significantly more frequent in the patients than controls (p < 0.012-0.0001). There were 13 muscles in which relevant conduction studies were abnormal and Vrms/T > or = 1.0 were the only abnormality of the needle EMG examination. In addition, a Vrms/T of > or = 1.0 was present in 10/14 muscles in which abnormalities might have been expected but where other needle EMG parameters were unremarkable and relevant nerve conductions normal. This study indicates that Vrms/T measurements can add meaningfully to the electrodiagnostic evaluation of neurogenic dysfunction.