Repetitive nerve stimulation as a diagnostic aid for distinguishing cervical spondylotic amyotrophy from amyotrophic lateral sclerosis

Quantitative evaluation of factors influencing the 3 Hz repetitive nerve stimulation test in patients with amyotrophic lateral sclerosis

INTRODUCTION/AIMS

Previous studies have suggested that treatments targeting the neuromuscular junction (NMJ) may play a role in the treatment of amyotrophic lateral sclerosis (ALS). However, factors impacting repetitive nerve stimulation (RNS), a technique to evaluate NMJ function, have yet to be fully elucidated. We aimed to identify independent factors contributing to the decremental response of the accessory nerve and evaluated its value in ALS clinical practice.

METHODS

A total of 626 patients who were diagnosed with ALS and underwent 3 Hz RNS tests on the accessory nerve were enrolled. Data on their clinical and electrophysiological indicators were divided into a training set (collected from June 2016 to December 2022) and a test set (collected from January to August 2023). Stepwise regression was used in independent variable selection and model building.

RESULTS

Forty-two percent of patients had a decrement larger than 10% and 24% had a decrement larger than 15%. Onset age, sex, onset site, forced vital capacity (FVC) and motor unit potential (MUP) duration were independent factors contributing to the results of the RNS test. MUP duration had the greatest impact on decremental response, followed by FVC and onset age. The decremental response in females was larger than in males. Upper limb onset was found to contribute more to the decrement than lower limb or bulbar onset.

DISCUSSION

In patients with ALS, NMJ safety factor is reduced during re-innervation. Decremental response is affected by multiple factors, which needs to be considered in clinical trials targeting the NMJ in these patients.

Analysis of surgical treatment of cervical spondylotic amyotrophy

Background

Cervical spondylotic amyotrophy (CSA) is a special type of cervical spondylosis based on cervical degeneration, which is mainly manifested by weakness and atrophy of upper limb muscles without obvious sensory impairment. Various diagnostic and treatment strategies used; however, discrepancies exist. We tried to discuss diagnosing and treating CSA.

Methods

15 patients with CSA were diagnosed in the Orthopedics Department of the First Affiliated Hospital of Zhengzhou University, aged 42-70 years old. The duration of preoperative symptoms of amyotrophy was 6 to 240 months. 12 patients received surgical treatment, and 3 patients received conservative treatment. The patients were divided into two groups according to the site of preoperative amyotrophy. The manual muscle test was used to evaluate the patients' muscle strength pre-and postoperatively.

Results

During postoperative follow-up, the muscle strength of 12 patients improved to different degrees compared to before surgery. The improvement effect was excellent in 2 cases, good in 6, and moderate in 4. There was no decrease in postoperative muscle strength compared with that before surgery. The satisfaction rate of the effect was 66.7%. The two groups had no statistically significant difference in preoperative muscle strength. The postoperative muscle strength of the proximal group was significantly better than that of the distal group.

Conclusion

The surgical effect of CSA of the proximal type is significantly better than that of the distal type. The recovery effect of amyotrophy after surgery for distal type CSA is poor; thus, surgical treatment should be carefully considered.

Cervical Spondylotic Amyotrophy Initially Misdiagnosed as Amyotrophic Lateral Sclerosis

A 63-year-old man diagnosed with mixed-type cervical spondylotic amyotrophy exhibited severe atrophy in the right biceps brachii, teres major, and intrinsic hand muscles, resulting in level 3 muscle weakness. Magnetic resonance imaging showed symmetrical high signal, also referred to as the snake eye sign. Previously, he was erroneously diagnosed with amyotrophic lateral sclerosis. He had undergone anterior cervical surgery 7 years prior. At present, his right upper limb muscles display minimal atrophy compared with the left, with muscle strength nearing level 4, which is considered normal. We believe that prompt surgical intervention on diagnosis of cervical spondylotic amyotrophy, along with comprehensive postsurgery rehabilitation, can halt further deterioration of the condition and accelerate recovery.

Clinical Utility of Repetitive Nerve Stimulation Test in Differentiating Multifocal Motor Neuropathy From Progressive Muscular Atrophy

OBJECTIVES

To evaluate the utility of repetitive nerve stimulation test (RNS) for differentiating multifocal motor neuropathy (MMN) and progressive muscular atrophy (PMA).

METHODS

We retrospectively enrolled 20 patients with MMN or PMA. We extracted the results of the initial 3-Hz RNS in the ulnar and accessory nerves and compared the percentage and frequency of abnormal decremental responses between both groups.

RESULTS

RNS was performed in 8 ulnar and 9 accessory nerves in patients with MMN, and in 8 ulnar and 10 accessory nerves in patients with PMA. Patients with MMN had a significantly lower decrement percentage (0.6 ± 4.0% in MMN vs. 10.3 ± 6.5% in PMA, P < 0.01) and frequency of abnormal decremental response (0 of 9 in MMN vs. 6 of 10 in PMA, P = 0.01) than patients with PMA in the accessory nerve.

CONCLUSIONS

The RNS has clinical utility for differentiating MMN from PMA.

Ultra-early amplitude decrement after repetitive nerve stimulation supports early neuromuscular junction injury in amyotrophic lateral sclerosis: a prospective cross-sectional study

The dying-back hypothesis holds that the damage to neuromuscular junctions and distal axons in amyotrophic lateral sclerosis occurs at the earliest stage of the disease. Previous basic studies have confirmed early damage to neuromuscular junctions, but it is difficult to obtain such evidence directly in clinical practice. In this prospective cross-sectional study, we recruited 22 patients with early amyotrophic lateral sclerosis with disease duration < 12 months and with clinical symptoms limited to the upper limbs. We also recruited 32 healthy controls. Repetitive nerve stimulation was performed, and patients were followed for 12 months. We found a significant change in the response to repetitive nerve stimulation in amyotrophic lateral sclerosis patients without spontaneous electromyographic activity. Patients that were prone to denervation had an increased decrement response of target muscles after repetitive nerve stimulation. These results suggest that changes in response to repetitive nerve stimulation may occur before denervation in amyotrophic lateral sclerosis patients. The damage to lower motor neurons is more obvious in patients with a higher percentage of repetitive never stimulation-related amplitude decrements. This study was approved by the Institutional Ethics Committee of Peking University Third Hospital (approval No. M2017198) on August 24, 2017.

Electrodiagnostic Assessment of Motor Neuron Disease

Motor neuron diseases involve degeneration of motor neurons in the brain (upper motor neurons), brain stem, and spinal cord (lower motor neurons). Symptoms vary depending on the degree of upper and lower neuron involvement, but progressive painless weakness is the predominant complaint. Motor neuron disease includes numerous specific disorders, including amyotrophic lateral sclerosis, spinal muscular atrophy, spinal bulbar muscular atrophy, and other inherited and acquired conditions. Abnormalities on nerve conduction studies, repetitive nerve stimulation, needle electromyography, and other electrodiagnostic techniques help to distinguish these disorders from each other, and from other disorders with progressive weakness.

Can the Large-Scale Decrement in Repetitive Nerve Stimulation Be Used as an Exclusion Criterion for Amyotrophic Lateral Sclerosis?

Objective: The objectives of this work were to identify the characteristics of repetitive nerve stimulation (RNS) in patients with amyotrophic lateral sclerosis (ALS) and further verify the electrophysiological exclusion criteria of ALS.

Methods: A total of 150 patients with ALS who were admitted to the Department of Neurology of Renmin Hospital of Wuhan University from January 2015 to December 2018 were enrolled. Clinical and electrophysiological data of the enrolled patients were collected. The differences in the amplitudes of the compound muscle action potential (CMAP) between the trapezius muscle (Trap) and the abductor digiti minimi (ADM) in low-frequency RNS were compared. Furthermore, we analyzed the associations between decremental responses and gender, onset age, duration of disease, onset site, Amyotrophic Lateral Sclerosis Functional Rating Scale—Revised (ALSFRS-R), disease progression rate, and CMAP amplitude.

Results: A significant decrement (≥20%) in at least one muscle was observed in 11.3% of the ALS patients, while decrements (≥10%) in at least one muscle were observed in 41.3%. The decremental percentage in the trapezius muscle was significantly higher than that in the abductor digiti minimi (P < 0.001). The onset age, duration of disease, onset site, and disease progression rate did not affect decremental responses. The decremental responses in RNS were more significant in ALS patients with low ALSFRS-R scores (P = 0.01). Moreover, there was a positive linear correlation between the CMAP amplitude and the decremental percentage of Trap and ADM in ALS patients.

Conclusions: CMAP decremental responses in RNS were common in ALS patients, suggesting abnormalities of neuromuscular junctions (NMJs). It is worthy of further discussion whether to consider a decrement >20% in RNS as a diagnostic exclusion criterion for ALS.

Preoperative factors that predict fair outcomes following surgery in patients with proximal cervical spondylotic amyotrophy. A retrospective study

STUDY DESIGN

Observational cohort study OBJECTIVES: To investigate preoperative factors that predict fair outcomes following surgery in patients with proximal cervical spondylotic amyotrophy (CSA) using electrophysiological and neurological findings.

SETTING

Yamaguchi University METHODS: 54 patients with proximal CSA who underwent surgical treatment of the cervical spine were enrolled. Erb-point stimulated compound muscle action potentials (CMAP) were recorded from the deltoid and biceps brachii muscles. We computed the ratio of affected to normal side CMAP amplitudes in two muscles (deltoid and biceps brachii) and regarded the mean ratio (CMAP-R) as representing the severity of neural involvement. Pre- and postoperative strengths of the most atrophic muscles were evaluated using manual muscle testing. Improvements in strength were classified as excellent (5 grades recovered), good (more than one grade recovered), fair (no improvement), or poor (worsened).

RESULTS

Surgical outcomes were excellent in 26 patients, good in five, fair in 16, poor in seven. Patients with fair outcomes had lower CMAP-R than those patients with excellent and good outcomes [P = 0.0099, odds ratio = 0.89 (95% confidence interval, 0.81-0.97; for a change of 10%)]. Eight patients (15%) had a C5 palsy.

CONCLUSIONS

CMAP-R could be used as a reliable predictive factor related to a fair surgical outcome. We must pay attention to the incidence of C5 palsy after surgery.

A New Diagnostic Medium for Cervical Spondylotic Myelopathy: Dynamic Somatosensory Evoked Potentials

OBJECTIVE

To identify and reveal the sensitivity and efficiency of dynamic somatosensory evoked potentials (DSSEPs) in the diagnosis of cervical spondylotic myelopathy (CSM).

METHODS

This retrospective study included 31 CSM and 15 control patients. All patients received SSEP examination with stimulation of median and ulnar nerves at neutral, flexed, and extended cervical positions; latency and amplitude were recorded at the C₂ and C₅ spinous processes and in the scalp over the primary sensory area (C_3'/4'). The percentage changes in latency and amplitude with dynamic motion were examined for each lead and compared between groups; the diagnostic cutoff values were determined using receiver operating characteristic curve analysis.

RESULTS

All the patients with CSM received surgeries and were followed up for 1 year. Amplitude parameters varied with a dynamic position in both groups; all recorded dynamic SSEP indices except right median stimulus recorded at C5 spinous process, right ulnar stimulus recorded at scalp point C3, and right ulnar stimulus recorded at C2 spinous process were significantly different between groups (P < 0.05), but latency was not (P > 0.05). At the neutral position, the amplitude of left media stimulus recorded at C2 spinous process (LMC₂) was associated with CSM, but with low diagnostic accuracy (area under the curve = 0.199). At a dynamic position, the percentage change in amplitude of LMC₂ and of left ulnar stimulus recorded at C2 spinous process (LUC₂) were determined to be diagnostic of CSM (P < 0.05), with areas under the curve of 0.891 and 0.912, respectively. Both records had high sensitivity and specificity in the diagnosis of CSM; the diagnostic cutoff values of LMC₂ and LUC₂ were calculated as 10.2% and 19.25%, respectively.

CONCLUSIONS

The percentage change in amplitude was obvious during cervical dynamic motion, with records from LMC₂ and LUC₂ being predictive of CSM diagnosis; dynamic SSEPs provided a simple, accurate, and noninvasive supplementary test for the diagnosis of complicated CSM.

Surgical outcomes for distal-type cervical spondylotic amyotrophy: a multicenter retrospective analysis of 43 cases

PURPOSE

Distal-type cervical spondylotic amyotrophy (CSA) is a rare form of cervical spondylosis that causes muscle weakness of upper extremities. The pathophysiology and appropriate surgical method for the treatment of CSA are still controversial. We investigated clinical outcomes in surgically treated distal-type CSA.

METHODS

The authors executed an analysis of the outcomes of 43 consecutive spinal surgeries performed in distal-type CSA patients. The duration of symptoms, perioperative manual muscle test (MMT) results, radiological findings, and perioperative complications were reviewed. We compared surgical outcomes between different approaches and examined the factors related to poor outcomes (MMT improvement ≤ 0) after surgery.

RESULTS

The pathophysiology of CSA was mostly caused by a combination of multiple lesions in the anterior horn and/or nerve root. Nineteen of 29 patients (65.5%) who received anterior approach methods were included in the good outcome group (MMT improvement ≥ 1), whereas 7 of 14 patients (50.0%) in the posterior group were classified as good. In the anterior group, the mean MMT grade significantly improved from 2.6 to 3.4 (p = 0.0035) despite the higher rate of complications. The duration of symptoms was substantially associated with poor outcomes. The MMT grade significantly improved from 2.2 to 3.2 (p = 0.0118) in the < 6 months group. Cervical alignments and preoperative MMT grade were not statistically associated with poor outcomes.

CONCLUSIONS

Patients with poor outcomes had symptoms for a longer duration. We found tolerable clinical outcomes within 6 months from onset. The anterior approaches might be recommended because this procedure significantly improved MMT levels in the hands. These slides can be retrieved under Electronic Supplementary Material.

Cervical spondylotic amyotrophy: a systematic review

PURPOSE

Cervical spondylotic amyotrophy (CSA) is characterized by upper limb muscle weakness and atrophy, without sensory deficits. The pathophysiology of CSA has been attributed to selective injury to the ventral nerve root and/or anterior horn of the spinal cord. This review aimed to delineate the history of CSA and to describe the epidemiology, etiology, pathophysiology, classification, clinical features, radiological and electrophysiological assessment, diagnosis, differential diagnosis, natural history and treatment of CSA.

METHODS

A comprehensive search of PubMed, EMBASE, Cochrane library and Web of Science databases was conducted, from their inception to April 3, 2018.

RESULTS

Clinically, CSA is classified into three types: a proximal-type (involving the scapular muscles, deltoid and biceps), a distal-type (involving the triceps and muscles of the forearm and hand) and a diffuse-type (involving features of both the distal- and proximal-type). Diagnosis requires documentation of muscle atrophy, without significant sensory deficits, supported by careful neurological, radiological and neurophysiological assessments, with amyotrophic lateral sclerosis, Parsonage-Turner syndrome, rotator cuff tear and Hirayama disease being the principle differential diagnoses. Conservative management of CSA includes cervical traction, neck immobilization and physical therapy, with vitamin B12 or E administration being useful in some patients. Surgical treatment, including anterior decompression and fusion or laminoplasty, with or without foraminotomy, is indicated after conservative treatment failure. Factors associated with a poor outcome include the distal-type CSA, long symptom duration, older age and greater preoperative muscle weakness.

CONCLUSION

Although the disease process of CSA is self-limited, treatment remains challenging, leaving scope for future studies. These slides can be retrieved under Electronic Supplementary Material.

Changes in Central Motor Conduction Time and Its Implication on Dysfunction of Distal Upper Limb in Distal-Type Cervical Spondylotic Amyotrophy

PURPOSE

Distal-type cervical spondylotic amyotrophy (CSA) is an uncommon syndrome associated with cervical spondylosis. The pathogenic mechanism of distal-type CSA is still unclear. The aim of the current study was to analyze central motor conduction time (CMCT) in the cases with distal-type CSA and to investigate the role of cervical cord compressive injury in the distal-type CSA.

METHODS

Both 28 cases with distal-type CSA and 21 healthy subjects accepted CMCT measures, motor unit number estimation, handgrip strength examination, and magnetic resonance imaging evaluation.

RESULTS

In this study, nine (9/28, 32.1%) cases with CSA presented with prolonged CMCT, and both reduced number of motor units and decreased handgrip strength were found in these 9 cases (P < 0.05). Magnetic resonance imaging evaluation showed that 7 of these 9 patients presented with proximal cervical cord compression with or even without distal selective compression consistent with segmental atrophy. A negative relationship between CMCT and both number of motor units and handgrip strength was found on the symptomatic side (P < 0.05), and there was a positive correlation between CMCT and amplitude of single motor unit potentials on the less symptomatic side (P < 0.05).

CONCLUSIONS

Corticospinal tract damage caused by proximal spinal cord compression may induce distal motor unit loss to worsen in some cases with distal-type CSA, which may contribute to the dysfunction of the distal upper limb in some cases with distal-type CSA. Therefore, treatment and rehabilitation efforts should account for both distal selective compression and proximal cord compression in distal-type CSA.

Repetitive Nerve Stimulation in Amyotrophic Lateral Sclerosis

Background

Nowadays, it is widely known that decremental responses in low-frequency repetitive nerve stimulation (LF-RNS) are frequently observed in patients with amyotrophic lateral sclerosis (ALS). The pathological mechanism of this phenomenon remains unknown. This study aimed to illuminate the features of RNS in Chinese patients with ALS.

Methods

Clinical and electrophysiological data of 146 probable and definite ALS patients who underwent RNS were retrospectively enrolled and analyzed. LF-RNS (3 Hz) was performed in trapezius, deltoid, abductor digiti minimi (ADM), quadriceps femoris, and tibialis anterior. High-frequency RNS (HF-RNS, 10 Hz) was performed only in ADM. The two-sample t-test and Chi-squared test were used for statistical analysis.

Results

Decremental responses to LF-RNS (≥10%) in at least one muscle were detected in 83 (56.8%) of the cases and were most commonly seen in trapezius and deltoid. The incidence of decremental response was higher in patients with upper limb onset. Incremental responses to HF-RNS (≥60%) in ADM were observed in 6 (5.6%) of the cases. In 106 muscles with decremental response, 62 (57.4%) muscles had a continuous decremental pattern, more than a U-shape pattern (37 cases, 34.3%). Nineteen cases showed definite decrements in LF-RNS tests in trapezius, while no abnormalities were found in the electromyography and neurological examination of the sternocleidomastoid muscle, supplied by the accessory nerve as well.

Conclusions

Decremental responses in the RNS are commonly observed in ALS patients. The findings regarding the trapezius indicated that some ALS onsets could be initiated by a "dying back" process, with destruction of neuromuscular junctions (NMJs) before motor neurons. Incremental responses in the ADM implied damage of the NMJs involved both the post and presynaptic membranes.

Influence of placement sites of the active recording electrode on CMAP configuration in the trapezius muscle

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The active recording electrode site influences the CMAP waveform of the trapezius muscle (TM).

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CMAP becomes high by placement of the active recording electrode 2 cm behind the belly of the TM.

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Volume conduction from the supraspinatus muscle affects the CMAP waveform of the TM.

Objective

We investigated how the active electrode placement site influences compound muscle action potential (CMAP) configuration of the upper trapezius muscle (TM).

Methods

A nerve conduction study of the accessory nerve was performed, and the CMAPs obtained with two different placement sites, i.e., placement of the active recording electrode on the belly of the upper TM (CMAP-A) and placement of the electrode 2 cm behind the belly (CMAP-B), were compared. CMAPs were also obtained with the active recording electrode placed in the supraspinous fossa (CMAP-C).

Results

All CMAPs were recorded from 21 healthy volunteers. The mean peak-to-peak amplitude of CMAP-B was 3.4 mV higher than that of CMAP-A (11.0 ± 4.0 mV vs. 14.4 ± 4.9 mV; P < 0.01). The mean peak-to-peak amplitude of CMAP-C was 10.3 ± 5.0 mV.

Conclusions

CMAP of the upper TM was always higher when the active recording electrode was placed 2 cm behind the belly of the muscle.

Significance

When stimulating the accessory nerve, a current spread occurs to the C5 spinal nerve root and another CMAP originating from the supraspinatus muscle occurs in the supraspinous fossa. The volume conduction from the supraspinatus muscle affects the active recording electrode on the TM, resulting in an increase in CMAP amplitude.