Artificial intelligence for automatic classification of needle EMG signals: A scoping review

OBJECTIVE

This scoping review provides an overview of artificial intelligence (AI), including machine and deep learning techniques, in the interpretation of clinical needle electromyography (nEMG) signals.

METHODS

A comprehensive search of Medline, Embase and Web of Science was conducted to find peer-reviewed journal articles. All papers published after 2010 were included. The methodological quality of the included studies was assessed with CLAIM (checklist for artificial intelligence in medical imaging).

RESULTS

51 studies were identified that fulfilled the inclusion criteria. 61% used open-source EMGlab data set to develop models to classify nEMG signal in healthy, amyotrophic lateral sclerosis (ALS) and myopathy (25 subjects). Only two articles developed models to classify signals recorded at rest. Most articles reported high performance accuracies, but many were subject to bias and overtraining.

CONCLUSIONS

Current AI-models of nEMG signals are not sufficient for clinical implementation. Suggestions for future research include emphasizing the need for an optimal training and validation approach using large datasets of clinical nEMG data from a diverse patient population.

SIGNIFICANCE

The outcomes of this study and the suggestions made aim to contribute to developing AI-models that can effectively handle signal quality variability and are suitable for daily clinical practice in interpreting nEMG signals.

The role of electrodiagnosis in focal neuropathies

Electrodiagnostic (EDX) testing plays an important role in confirming a mononeuropathy, localizing the site of nerve injury, defining the pathophysiology, and assessing the severity and prognosis. The combination of nerve conduction studies (NCS) and needle electromyography findings provides the necessary information to fully assess a nerve. The pattern of NCS abnormalities reflects the underlying pathophysiology, with focal slowing or conduction block in neuropraxic injuries and reduced amplitudes in axonotmetic injuries. Needle electromyography findings, including spontaneous activity and voluntary motor unit potential changes, complement the NCS findings and further characterize chronicity and degree of axon loss and reinnervation. EDX is used as an objective marker to follow the progression of a mononeuropathy over time.

Changes in electrophysiological findings of spinal muscular atrophy type I after the administration of nusinersen and onasemnogene abeparvovec: two case reports

BACKGROUND

Recently, there have been significant advances in the treatment of spinal muscular atrophy (SMA). Although clinical improvement in patients with SMA after the treatment has been reported, changes in electrophysiological findings, especially needle electromyography (EMG), have rarely been reported. Herein, we report the posttreatment changes in EMG and nerve conduction study findings over time in two patients with SMA type I.

CASE PRESENTATION

Patient 1: A 2.5-year-old girl was diagnosed with SMA type I at 1 month of age. She received nusinersen four times and onasemnogene abeparvovec (OA) was administered at 6 months of age. The compound muscle action potential (CMAP) amplitudes of the median and tibial nerves increased over time. The needle EMG after the treatment showed high-amplitude motor unit potentials (MUPs) suggestive of reinnervation during voluntary contraction, which were not seen before the treatment. However, fibrillation potentials at rest were still seen after the treatment. Patient 2: A 2-year-old girl was diagnosed with SMA type I at 6 months of age. She had received nusinersen two times and OA was administered at 7 months of age. The CMAP amplitudes and the MUPs presented similar changes as presented in Case 1.

CONCLUSION

This is the first report on the changes in needle EMG findings after treatment in patients with SMA type I. These findings suggested that peripheral nerve reinnervation occurred after the treatment, although active denervation was still present. The accumulation of these findings will be important for evaluating the effectiveness of treatment for SMA in the future.

Electrophysiological assessment of respiratory function

While the traditional lung function tests are used to assess lung capacity and pulmonary function, they cannot evaluate respiratory driving function and the integrity of the conduction pathway from the central nervous system to the respiratory motor neuron in the spinal cord and to the diaphragm. The inspiratory trigger is sent from the central nervous system through the phrenic nerve and drives the diaphragm to generate inspiratory movement. Therefore, phrenic nerve stimulation and diaphragmatic electromyography are two fundamental methods to assess respiratory function. There are several useful tools to assess respiratory motor system including electrical or magnetic phrenic nerve stimulation, diaphragmatic needle electromyography, and diaphragmatic ultrasound. By these means, physicians can assess current respiratory status in different neurological diseases that affect respiratory muscles, follow-up of the severity of respiratory impairment, help to predict the chance of successfully weaning from ventilatory support, and confirm clinical diagnoses such as diaphragmatic myoclonus. Although some of these tests require special training, applying these neurophysiological assessments in clinical practice is highly recommended.

Treatment of progressive paralysis associated with cervical myelopathy and suspected amyotrophic lateral sclerosis: A case report

Background:

Amyotrophic lateral sclerosis (ALS) is an intractable progressive disease, with an incidence of 2.2– 2.3 per 100,000 individuals, which is not extremely low. ALS symptoms are accompanied by spinal myeloradicular motor deficit; its differential diagnosis is must because progressive paralysis needs emergency surgery.

Case Description:

A 64-year-old man with suspected ALS showing progressive paralysis with cervical myelopathy was diagnosed as normal after performing a nerve conduction study preoperatively. Postoperative diffuse fasciculation after posterior decompression allowed the diagnosis of ALS through needle electromyography (EMG). Thereafter, the patient’s condition slowly deteriorated and he died after 16 months.

Conclusion:

Surgery might aggravate ALS symptoms; however, surgery for progressive paralysis in patients with suspected ALS is required for distinguishing patients with non-ALS paralysis. Approximately 70% of cases have spinal-onset ALS lacking typical cranial nerve symptoms; thus, to prevent unnecessary surgery, surgeons should at least know the characteristic features of ALS and should be aware that early diagnosis requires needle EMG for definitive diagnosis of ALS.

Needle Electromyography Waveforms During Needle Electromyography

Needle electromyography (EMG) waveforms recorded during needle EMG help to define the type, temporal course, and severity of a neuromuscular disorder. Accurate interpretation of EMG waveforms is a critical component of an electrodiagnostic examination. This article reviews the significance of spontaneous EMG waveforms and changes in voluntary motor unit potentials in neuromuscular disorders.

Electrodiagnostic Assessment of Polyneuropathy

This article focuses on principles of nerve conduction studies and needle electromyography applied to the electrodiagnosis of polyneuropathy. The components of the electrodiagnostic evaluation of polyneuropathy and the electrophysiological characteristics of axonal and demyelinating neuropathies and nodo-paranodopathies are reviewed.

Reduction in median nerve cross-sectional area at the forearm correlates with axon loss in carpal tunnel syndrome

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The median nerve CSA at the forearm is smaller when CTS is involved with axon loss.

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WFR of the median nerve is highest when CTS causes slight axon loss.

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Axon loss of the median nerve in CTS hampers the diagnostic value of wCSA and WFR.

Objective

To explore the relationship between axon loss and measured cross-sectional areas of the median nerve (MN) in severe carpal tunnel syndrome (CTS).

Methods

In this retrospective study of 158 examined wrists, we compared axon loss to the ultrasound parameters MN cross-sectional area at the wrist (wCSA), MN cross-sectional area at the forearm (fCSA) and wrist-to-forearm ratio (WFR), in patients with moderate to extreme CTS. Axon loss was evaluated by needle electromyography (EMG) of the abductor pollicis brevis muscle (spontaneous activity and reduction of interference pattern).

Results

Both the spontaneous activity and interference pattern reduction correlated negatively to fCSA (r = −0.189, p = 0.035; r = −0.210, p = 0.019; respectively). In moderate CTS, both the spontaneous activity and interference pattern reduction correlated positively to WFR (r = 0.231, p = 0.048; r = 0.232, p = 0.047; respectively). The WFR was highest when slight spontaneous activity was detected. Neither wCSA nor WFR correlated with axon loss in severe and extreme CTS.

Conclusions

The fCSA is smaller when axon loss in CTS is more prominent. The WFR is highest when CTS is associated with slight axon loss of the MN.

Significance

CTS might cause retrograde axonal atrophy detected as small fCSA. Prominent axon loss in CTS may reduce the diagnostic value of WFR.

Preoperative electrophysiologic assessment of C5-innervated muscles in predicting C5 palsy after posterior cervical decompression

PURPOSE

To investigate the feasibility of both needle electromyography (EMG) and proximal nerve conduction studies (NCS) in predicting C5 palsy after posterior cervical decompression.

METHODS

This study included 192 patients with cervical myelopathy undergoing laminoplasty or laminectomy. Preoperatively, all patients accepted bilateral needle EMG detection and proximal NCS that consisted of supramaximally stimulating Erb's point and recording compound muscle action potential (CMAP) from bilateral deltoid.

RESULTS

In the present study, 11 (11/192, 5.7%) patients developed unilateral C5 palsy after operation, and more patients with C5 palsy showed abnormal spontaneous activity in C5-innervated muscles compared to those without C5 palsy (8/11 vs. 16/181, p < 0.05). The sensitivity and specificity of spontaneous activity in C5-innervated muscles in predicting postoperative C5 palsy were 72.7% and 91.2%, respectively. Furthermore, there were significant left-to-right differences of deltoid CMAP amplitudes between the patients with and without C5 palsy (p < 0.05), and this measurement was also demonstrated to be useful for distinguishing patients with C5 palsy from cases without C5 palsy by receiver operating characteristic (ROC) curve analysis (cut-off value: 2.1 mV, sensitivity: 63.6%; specificity: 95.0%). In addition, the sensitivity and specificity of a series application of these two measurements were 63.6% and 100.0%, respectively.

CONCLUSIONS

The findings of this study support the hypothesis that pre-existing progressive C5 root injury may be a risk factor for C5 palsy after posterior cervical decompression. Clinically, the estimation of NCS and needle EMG in C5-innervated muscles may provide additional useful information for predicting C5 palsy after cervical spinal surgery.

LEVEL OF EVIDENCE I

Diagnostic: individual cross-sectional studies with the consistently applied reference standard and blinding.

The needle electromyography findings in the neurophysiological classification of ulnar neuropathy at the elbow

Background/aim

Although ulnar neuropathy at the elbow (UNE) is the second most common entrapment mononeuropathy, there are few reports on its neurophysiological classification. In this study, we tried to find out the role of needle electromyography (EMG) in the neurophysiological classification of UNE.

Materials and methods

UNE patients who met the clinical and neurophysiological diagnostic criteria and healthy individuals were included in this study. Reference values of nerve conduction studies were obtained from healthy individuals. Needle EMG was performed to all UNE patients. According to the neurophysiological classification proposed by Padua, UNE patients were classified as mild, moderate, and severe.

Results

Thirty-one controls and thirty-five UNE patients were included in the study. There was mild UNE in 23 patients, moderate UNE in 8, and severe UNE in 4. Abnormal needle EMG findings were present in all patients with moderate and severe UNE and in 12 patients with mild UNE.

Conclusion

Abnormal needle EMG findings are seen in most of the UNE patients. Therefore, it is not practical to use needle EMG findings in the neurophysiological classification. Needle EMG abnormalities may also be present in patients with mild UNE due to axonal degeneration or motor conduction block.

Needle EMG muscle identification: A systematic approach to needle EMG examination

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The article discusses standard EMG examination techniques.

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Special clinical and safety concerns, (e.g. bleeding diatheses) are addressed.

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The complementary role of ultrasound is reviewed.

The proper performance of needle electromyography (EMG) requires that the examiner obtain a brief but comprehensive history, perform a directed examination and generate a short differential diagnosis as part of the initial patient encounter. Equally as important is to set reasonable expectations for this study’s performance as electronic media do not necessarily portray all of the nuances of an electrodiagnostic study. In addition to these preliminary steps, this minimonograph discusses equipment used in EMG evaluations, EMG examination techniques, muscles commonly sampled, pain reduction techniques, and special considerations that may require study modification such as anticoagulation, lymphedema, obesity and supervening infection. Clinicians performing these studies will maximize useful data collection while minimizing patient discomfort if all of these recommendations are followed.

Deep learning for waveform identification of resting needle electromyography signals

OBJECTIVE

Given the recent advent in machine learning and artificial intelligence on medical data analysis, we hypothesized that the deep learning algorithm can classify resting needle electromyography (n-EMG) discharges.

METHODS

Six clinically observed resting n-EMG signals were used as a dataset. The data were converted to Mel-spectrogram. Data augmentation was then applied to the training data. Deep learning algorithms were applied to assess the accuracies of correct classification, with or without the use of pre-trained weights for deep-learning networks.

RESULTS

While the original data yielded the accuracy up to 0.86 on the test dataset, data-augmentation up to 200,000 training images showed significant increase in the accuracy to 1.0. The use of pre-trained weights (fine tuning) showed greater accuracy than "training from scratch".

CONCLUSIONS

Resting n-EMG signals were successfully classified by deep-learning algorithm, especially with the use of data augmentation and transfer learning techniques.

SIGNIFICANCE

Computer-aided signal identification of clinical n-EMG testing might be possible by deep-learning algorithms.

Fasciculation potentials and decremental responses in amyotrophic lateral sclerosis

OBJECTIVE

The positive correlation between fasciculation potentials (FPs) and decremental responses in repetitive nerve stimulation test (RNS) in amyotrophic lateral sclerosis (ALS) patients has been described based on only one past study. We revisited this issue.

METHODS

Subjects consisted of 30 prospectively-enrolled ALS patients on whom both needle EMG and RNS were conducted in the same trapezius muscle. Fasciculation potentials (FPs) were identified off-line from the restored 3-min signal. Firing rate of FPs (FR-FP) per minute was calculated from the total count of FPs of different origins. Correlations between FR-FP, decremental percentage (Decr%) and the amplitude of the initial compound muscle action potential (CMAPamp) in RNS were investigated.

RESULTS

There was no correlation between FR-FP and Decr% (r = 0.03) or between FR-FP and CMAPamp (r = 0.04). A significant negative correlation was observed between CMAPamp and Decr% (r = -0.56, P < .005).

CONCLUSION

FPs are not correlated with the decremental response in RNS.

SIGNIFICANCE

The underlying mechanism for FPs and decremental responses in ALS must be different and unrelated to each other.

Amyotrophic lateral sclerosis with a sudden-onset history

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We reported on two patients with ALS with a sudden-onset history.

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Marked weakness of the extensor digitorum with relatively mild weakness of the other muscles was characteristic.

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The risk of initial misdiagnosis is high for such patients.

Objective

We report on two patients with amyotrophic lateral sclerosis (ALS) complaining of sudden-onset difficulty in finger elevation.

Case report

A 65-year-old man (the first patient) and a 66-year-old man (the second patient) suddenly became aware of difficulty in finger elevation of one hand. They were not aware of any other symptoms prior to the onset. In the first patient, cerebral infarction at the precentral gyrus was initially suspected. In the second patient, cervical spondylosis was initially suspected, and cervical spine surgery was planned. However, needle EMG revealed widespread neurogenic changes and abundant fasciculation potentials for both patients. Widespread weakness emerged in time and relentlessly progressed, and finally the diagnosis of ALS was made. In both cases, notable weakness in the extensor digitorum (ED) muscle with relatively mild weakness in the other muscles in the affected limb was a characteristic finding. Loss of one motor unit in ED that has already enlarged due to reinnervation must have caused sudden awareness of the weakness.

Significance

Clinicians should recognize the presence of ALS patients with a sudden-onset history because the risk of initial misdiagnosis is high for such patients.

Diagnostic accuracy of multifidus muscle spontaneous activity by needle electromyography for the detection of lumbar foraminal and lateral exit-zone stenosis

PURPOSE

The medial branch of the posterior ramus of the lumbar spinal nerve is well known to be innervated independently and to end in the multifidus muscle without anastomosis. This prospective cohort study aimed to determine the diagnostic specificity and sensitivity of multifidus muscle denervation (MMD) by needle electromyography (N-EMG) for lumbar foraminal and lateral exit-zone stenosis (LF/LEZS).

METHODS

We enrolled 61 consecutive patients experiencing unilateral dysesthesia and/or leg pain in the L4 or L5 regions with suspicious LF/LEZS. The Japanese Orthopedic Association (JOA) score, Visual Analog Scale (VAS) for leg pain, and N-EMG were examined. In this study protocol, all patients received at least 3 months of conservative therapy. Surgery was performed on patients who experienced less than 50% VAS pain relief compared with their initial score after confirming the responsible level by lumbar nerve root block. The specificity of N-EMG was the proportion of patients who improved with conservative therapies (non-surgery) after 3 months. The sensitivity of N-EMG was the proportion of patients who improved with surgical therapies (surgery) after more than 12 months.

RESULTS

Twenty-three patients underwent surgery. The initial lower JOA, positive Kemp test and motor weakness were significantly higher in the surgery group. The MMD by N-EMG indicated that 34 of 38 patients were negative in the non-surgery group. In the surgery group, 21 of 23 patients were positive. The diagnostic sensitivity and specificity were 91.3 and 92.1%, respectively.

CONCLUSIONS

Needle electromyography is a simple and available additional method for the diagnosis of LF/LEZS.

Myotonic discharges discriminate chloride from sodium muscle channelopathies

Non-dystrophic myotonic syndromes represent a heterogeneous group of clinically quite similar diseases sharing the feature of myotonia. These syndromes can be separated into chloride and sodium channelopathies, with gene-defects in chloride or sodium channel proteins of the sarcolemmal membrane. Myotonia has its basis in an electrical instability of the sarcolemmal membrane. In the present study we examine the discriminative power of the resulting myotonic discharges for these disorders. Needle electromyography was performed by an electromyographer blinded for genetic diagnosis in 66 non-dystrophic myotonia patients (32 chloride and 34 sodium channelopathy). Five muscles in each patient were examined. Individual trains of myotonic discharges were extracted and analyzed with respect to firing characteristics. Myotonic discharge characteristics in the rectus femoris muscle almost perfectly discriminated chloride from sodium channelopathy patients. The first interdischarge interval as a single variable was longer than 30 ms in all but one of the chloride channelopathy patients and shorter than 30 ms in all of the sodium channelopathy patients. This resulted in a detection rate of over 95%. Myotonic discharges of a single muscle can be used to better guide toward a molecular diagnosis in non-dystrophic myotonic syndromes.

Assessment of Effective Ankle Joint Positioning in Strength Training for Intrinsic Foot Flexor Muscles: A Comparison of Intrinsic Foot Flexor Muscle Activity in a Position Intermediate to Plantar and Dorsiflexion with that in Maximum Plantar Flexion Using Needle Electromyography

[Purpose] The effectiveness of intrinsic foot flexor strength training performed in the plantar flexion position was examined using needle electromyography. [Subjects] The subjects of this study were 18 healthy men. [Methods] We used needle electromyography to measure the muscle activities of the flexor hallucis brevis (FHB), and the flexor digitorum brevis (FDB) in maximum plantar and an intermediate position. [Results] Significant increases in muscle activities were observed for both FHB and FDB, and the rates of increase from the intermediate position to the plantar flexion position were 43% for FHB and 46% for FDB. [Conclusion] This study demonstrated that it is possible to evaluate intrinsic foot flexors, in addition to the numerous reports on treatment methods focusing on extrinsic foot flexors. Furthermore, the results suggest that toe flexion exercises performed during plantar flexion of the ankle joint are an effective method for intrinsic foot flexor strength training.

Rapidly progressive amyotrophic lateral sclerosis initially masquerading as a demyelinating neuropathy

Rare cases of demyelinating neuropathy have been described in association with amyotrophic lateral sclerosis (ALS). We report two patients with typical ALS whose initial electroneuromyographic (ENMG) presentation could suggest the existence of a process of motor nerve fiber demyelination. However, subsequent ENMG examinations and the fatal course of the disease in a few months rather supported severe ongoing axonal degeneration at the origin of motor nerve conduction abnormalities. Repeated examinations could be required to distinguish between ENMG features of concomitant demyelinating neuropathy and rapidly progressive motor neuron loss in ALS.