Nerve Conduction Studies: Basic Concepts and Patterns of Abnormalities

Neuromuscular electrical stimulation for the treatment of diabetic sensorimotor polyneuropathy: A prospective, cohort, proof-of-concept study

OBJECTIVE

To assess a potential efficacy signal, safety and feasibility of neuromuscular electrical stimulation (NMES) therapy as an adjunct to standard care in patients with diabetic sensorimotor polyneuropathy (DSPN).

METHODS

In this single-centre, prospective, cohort, proof-of-concept study, 25 patients with DSPN consented to at least one daily 30-minute NMES therapy session (Revitive® IX) for 10 weeks, with 20 patients completing the study. The primary outcome measure was nerve conductivity assessed using a nerve conduction study of the sural, superficial peroneal, common peroneal and tibial nerves at 10 weeks compared to baseline. Secondary outcomes included superficial femoral artery (SFA) haemodynamics during NMES therapy compared to rest and quality-of-life at 10 weeks compared to baseline.

RESULTS

At 10 weeks, there were significant increases in sural sensory nerve action potential amplitude and conduction velocity (p < 0.001), superficial peroneal sensory nerve action potential amplitude (p = 0.001) and conduction velocity (p = 0.002), common peroneal nerve conduction velocity (p = 0.004) and tibial nerve compound muscle action potential amplitude (p = 0.002) compared to baseline. SFA volume flow and time-averaged mean velocity significantly increased (p ≤ 0.003) during NMES compared to rest. Patient-reported Michigan Neuropathy Screening Instrument scores significantly decreased (p = 0.028) at 10 weeks compared to baseline. Three unrelated adverse events occurred, and 15 participants adhered to treatment.

CONCLUSIONS

NMES therapy as an adjunct to standard care for 10 weeks significantly increased lower limb nerve conductivity in patients with DSPN and may be beneficial in the treatment of DSPN.

Current understanding of the molecular mechanisms of chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is the most common off-target adverse effects caused by various chemotherapeutic agents, such as cisplatin, oxaliplatin, paclitaxel, vincristine and bortezomib. CIPN is characterized by a substantial loss of primary afferent sensory axonal fibers leading to sensory disturbances in patients. An estimated of 19-85% of patients developed CIPN during the course of chemotherapy. The lack of preventive measures and limited treatment options often require a dose reduction or even early termination of life-saving chemotherapy, impacting treatment efficacy and patient survival. In this Review, we summarized the current understanding on the pathogenesis of CIPN. One prominent change induced by chemotherapeutic agents involves the disruption of neuronal cytoskeletal architecture and axonal transport dynamics largely influenced by the interference of microtubule stability in peripheral neurons. Due to an ineffective blood-nerve barrier in our peripheral nervous system, exposure to some chemotherapeutic agents causes mitochondrial swelling in peripheral nerves, which lead to the opening of mitochondrial permeability transition pore and cytochrome c release resulting in degeneration of primary afferent sensory fibers. The exacerbated nociceptive signaling and pain transmission in CIPN patients is often linked the increased neuronal excitability largely due to the elevated expression of various ion channels in the dorsal root ganglion neurons. Another important contributing factor of CIPN is the neuroinflammation caused by an increased infiltration of immune cells and production of inflammatory cytokines. In the central nervous system, chemotherapeutic agents also induce neuronal hyperexcitability in the spinal dorsal horn and anterior cingulate cortex leading to the development of central sensitization that causes CIPN. Emerging evidence suggests that the change in the composition and diversity of gut microbiota (dysbiosis) could have direct impact on the development and progression of CIPN. Collectively, all these aspects contribute to the pathogenesis of CIPN. Recent advances in RNA-sequencing offer solid platform for in silico drug screening which enable the identification of novel therapeutic agents or repurpose existing drugs to alleviate CIPN, holding immense promises for enhancing the quality of life for cancer patients who undergo chemotherapy and improve their overall treatment outcomes.

Effect of 2% Topical Lidocaine Gel on Discomfort from Electrical Stimulation During Nerve Conduction Studies- A Prospective Double-Blind Placebo-Controlled Study

Purpose

Procedure discomfort can limit electrodiagnostic studies. Reducing discomfort can maximize the benefits of these diagnostic tools. This study targeted the discomfort associated with nerve conduction studies (NCS).

Patients and Methods

This was a prospective randomized double-blind placebo-controlled study comparing the effect of topical lidocaine gel (2%) versus analgesic-free lubricant gel (K-Y gel) on pain perception during NCS. Sequential patients (n=130) referred for routine NCS participated in the study. We applied 1 mL of lidocaine gel to one palm, and 1 mL of K-Y gel to the other as a control. After 20-45 min of application, graded increments of electrical stimulation intensity were delivered to record the median and ulnar mixed palmar nerve responses. Patients were then asked to score the degree of pain felt from electrical stimulation over each palm using the Wong-Baker Faces Pain Scale (WBFPS) and the Numeric Rating Scale (NRS), independent of baseline pain.

Results

Mean WBFPS and NRS scores for lidocaine-treated palms were significantly lower than those for controls using parametric paired t-test (3.79 vs 4.37 and 3.35 vs 3.78 respectively, all p-values<0.05). Subgroup analysis showed a significant decrease in mean scores in females, patients aged ≤50 years, patients without a history of previous NCS, and patients without comorbidities (all p-values<0.05). Median scores using nonparametric Wilcoxon ranked test also showed statistically significant differences (all p-values<0.05).

Conclusion

The results indicate that topical lidocaine 2% gel reduces discomfort associated with NCS. However, despite the statistical significance, clear clinical significance may be lacking. Clinical implementation may be considered for the subgroups that showed the greatest benefit. Further studies that incorporate more efficient drug delivery methods may yield better results.

Longitudinal traumatic peripheral nerve injury recovery: quantitative description, classification and prediction

Aim: Repair of peripheral nerves is recommended following transection. Systematic evaluation of longitudinal recovery in injury models is needed to improve patient management. Gompertz function provided straightforward interpretation and prediction of recovery outcomes. Materials & methods: Behavioural sciatic function index, measured 3 days post injury, and weekly for 12 weeks following full nerve transection and repair (n = 6) as well as crush injuries (n = 6). Results: Gompertz parametrization provided early classification between types of traumatic peripheral nerve injuries following surgical repair. Results distinguished injury nerves (A: p < 0.01; T_i: p < 0.05; Ic: p < 0.05 and outcome: p < 0.01). Early prognostication of outcomes (crush: 5.5 ± 0.3 and cut/repair: 8 ± 1 weeks) preceded current methods. Conclusion: Our findings identify injury type, state of recovery and early prognostication of outcome.

Median Nerve Recovery and Morphological Change on MRI at 24 Months after Open Carpal Tunnel Release

Background: This study aimed to investigate the relationship between postoperative clinical results and long-term morphological changes in patients with carpal tunnel syndrome (CTS) as observed on magnetic resonance imaging (MRI) before and after open carpal tunnel release (OCTR). Methods: We retrospectively analysed data for 28 hands that had undergone OCTR with at least 24 months of follow-up data. Two-point discrimination (2PD) test results were examined for the first three fingers, as were the distal motor latency (DML) and sensory conduction velocity (SCV) of the median nerve. We also calculated the cross-sectional area (CSA) of the carpal tunnel and the distance from the median nerve to the volar carpal bone at the hamate and the pisiform levels using MRI images. Variables were compared before and 24 months after OCTR. Results: Significant improvements in all variables were observed, including average 2PD scores (Finger I: 13.1 ± 6.2 vs. 7.7 ± 4.3, p < 0.01, Finger II: 11.9 ± 6.6 vs. 7.0 ± 3.5, p < 0.01, Finger III: 13.6 ± 6.1 vs. 7.8 ± 4.5, p < 0.01), average DML (8.3 ± 3.3 vs. 4.3 ± 0.6 m/s, p < 0.01), average SCV (30.8 ± 11.0 vs. 41.3 ± 5.3 m/s, p < 0.01), CSA of the carpal tunnel (hamate level: 194.9 ± 30.6 vs. 254.2 ± 47.6 mm2, p < 0.01, pisiform level: 244.2 ± 46.5 vs. 274.7 ± 75.1 mm2, p = 0.01) and the distance between the median nerve and volar carpal bone (hamate level: 8.7 ± 1.4 vs. 11.2 ± 1.6 mm, p < 0.01, pisiform level: 11.8 ± 1.7 vs. 13.8 ± 2.5 mm, p < 0.01). Conclusions: Our results demonstrate that OCTR is successful in achieving long-term decompression and recovery of the median nerve in patients with CTS. Level of Evidence: Level III (Therapeutic).

Pathogenic PSAT1 Variants and Autosomal Recessive Axonal Charcot-Marie-Tooth Disease With Ichthyosis

BACKGROUND

Biallelic pathogenic phosphoserine aminotransferase 1 (PSAT1) variants generally cause a severe phenotype predominantly involving the central nervous system. Here, for the first time, we report two patients harboring pathogenic PSAT1 variants only manifested as polyneuropathy and ichthyosis.

METHODS

Two patients from unrelated families presenting with polyneuropathy and ichthyosis were enrolled. Whole exome sequencing was performed to identify possible disease-causing variants. Their clinical, electrophysiological, imaging, biochemical, and pathologic changes were in detail assessed and investigated.

RESULTS

Homozygous variant c.43G>C and compound heterozygous variants c.112A>C and c.43G>C in PSAT1 were identified in patients 1 and 2, respectively. Nerve conduction studies revealed preserved or mild slowing motor nerve conduction velocities of the median nerves in the two patients, whereas the compound motor action potential in patient 1 was severely decreased. Brain magnetic resonance imaging of the two patients found no abnormalities. Median nerve enlargement was observed on ultrasound in patient 1. Both patients had normal level of serine and glycine in plasma and cerebrospinal fluid. Sural nerve biopsy found severe loss of myelinated fibers. Electron microscopy revealed neurofilament accumulation and mitochondrial aggregation in axons. Both variants in PSAT1 were classified as likely pathogenic or pathogenic variants according to the standard guidelines.

CONCLUSIONS

Our study confirms that pathogenic PSAT1 variants can cause a mild phenotype, predominantly as autosomal recessive axonal Charcot-Marie-Tooth disease.

Eyelid myokymia caused by a trigeminal schwannoma as determined by the trigeminal-evoked blink reflex

A 57-year-old man had trigeminal schwannoma in Meckel's cave with eyelid myokymia only. The evaluation of the trigeminal-evoked blink reflex was useful for confirming eyelid myokymia and contributed to surgical decision-making. In patients with persistent eyelid myokymia, neurophysiological and imaging evaluations may be useful for determining the underlying pathophysiology.

Radial nerve compression: anatomical perspective and clinical consequences

The radial nerve is the biggest branch of the posterior cord of the brachial plexus and one of its five terminal branches. Entrapment of the radial nerve at the elbow is the third most common compressive neuropathy of the upper limb after carpal tunnel and cubital tunnel syndromes. Because the incidence is relatively low and many agents can compress it along its whole course, entrapment of the radial nerve or its branches can pose a considerable clinical challenge. Several of these agents are related to normal or variant anatomy. The most common of the compressive neuropathies related to the radial nerve is the posterior interosseus nerve syndrome. Appropriate treatment requires familiarity with the anatomical traits influencing the presenting symptoms and the related prognoses. The aim of this study is to describe the compressive neuropathies of the radial nerve, emphasizing the anatomical perspective and highlighting the traps awaiting physicians evaluating these entrapments.

Safety of Laryngeal Electromyography and Repetitive Stimulation

OBJECTIVES

Laryngeal Electromyography (LEMG) is a procedure used to assess electrical signals from laryngeal muscles. It is considered to be the gold standard test for examining vocal fold paresis/paralysis. Repetitive stimulation studies, which usually are performed at the time of LEMG, can aid in assessment of neuromuscular function. Electromyography poses risks to the patient due to the use of electricity and needles. The purpose of this paper was to evaluate the safety of LEMG and discuss the possible complications.

METHODS

This was a retrospective review of patients from January 2015 through February 2022. Information from patient charts included age, sex, chief complaint, past medical history, family medical history, medications, social history, strobovideolaryngoscopy results, type of paresis, professional voice user status, presence of pacemaker, laryngeal electromyography and repetitive stimulation study results, and reported complications. Complications were considered to be anything that differed from the norm. Pain was included as a complication. Data were analyzed for relationships and significance.

RESULTS

Five hundred patients were included. Eighteen of the 500 (3.6%) experienced complications. Four (2.1%) males and 14 (4.5%) females experienced complications. Nine of the 18 (50%) reported pain after the procedure, 1 (5.56%) had excessive bleeding (controlled with pressure), 5 (27.78%) reported voice changes, and 3 (16.67%) experienced difficulty with completion of the procedure. No patients with pacemakers or patients taking anticoagulants had complications, but repetitive stimulation studies were not performed on patients with pacemakers.

CONCLUSIONS

LEMG and repetitive stimulation studies are safe and effective procedures to examine laryngeal muscles. Repetitive stimulation studies are not recommended for patients with pacemakers.

Non-Invasive Muscular Atrophy Causes Evaluation for Limb Fracture Based on Flexible Surface Electromyography System

Muscular atrophy after limb fracture is a frequently occurring complication with multiple causes. Different treatments and targeted rehabilitation procedures should be carried out based on the causes. However, bedside evaluation methods are invasive in clinical practice nowadays, lacking reliable non-invasive methods. In this study, we propose a non-invasive flexible surface electromyography system with machine learning algorithms to distinguish nerve-injury and limb immobilization-related atrophy. First, a flexible surface electromyography sensor was designed and verified by in vitro tests for its robustness and flexibility. Then, in vivo tests on rats proved the reliability compared with the traditional invasive diagnosis method. Finally, this system was applied for the diagnosis of muscular atrophy in 10 patients. The flexible surface electromyography sensor can achieve a max strain of 12.0%, which ensures close contact with the skin. The in vivo tests on rats show great comparability with the traditional invasive diagnosis method. It can achieve a high specificity of 95.28% and sensitivity of 98.98%. Application on patients reaches a relatively high specificity of 89.44% and sensitivity of 91.94%. The proposed painless surface electromyography system can be an easy and accurate supplementary for bedside muscular atrophy causes evaluation, holding excellent contact with the body.

Impaired Vascular Endothelial Function is Associated with Peripheral Neuropathy in Patients with Type 2 Diabetes

PURPOSE

It is believed that vascular endothelial dysfunction is involved in the occurrence of cardiovascular disease (CVD), and diabetic peripheral neuropathy (DPN) is associated with flow-mediated dilation (FMD), however, the correlation is still unclear. Aims of the present study is to explore the relationship between DPN parameters and FMD, providing a new approach for the prevention of CVD.

PATIENTS AND METHODS

A total of 272 patients with T2DM from the Department of Endocrinology of The First Hospital of Lanzhou University according to the grading criteria were selected. FMD was measured by a new vascular ultrasound system and patients were divided into FMD>7%, 4%≤FMD≤7%, and FMD<4% groups. The Toronto Clinical Scoring System (TCSS) was used to assess the severity of DPN. The nerve conduction studies (NCS) assessed large fibre neuropathy by nerve conduction velocity (CV), compound muscle action potential (CMAP) amplitude (Amp), and distal motor latency (DML). SPSS 25.0 was used for statistical analysis.

RESULTS

TCSS evaluation revealed that the percentage of patients with severe nerve injury was significantly higher in FMD<4% (70%) compared to FMD>7% (2%). Among the TCSS indicators of all subjects, the proportion of temperature disturbance was the most (73%), and joint position disturbance was the least (0). TCSS scores were negatively correlated with FMD (r=-0.756, p<0.001). More interesting, in FMD<4% group, CV and Amp were positively correlated with FMD, while DML was negatively correlated (p<0.05). Linear regression analysis model showed that different systolic blood pressure (SBP), triglyceride (TG), TCSS and CV had statistically different effects on FMD.

CONCLUSION

High TCSS score and decreased CV of common peroneal and tibial nerves are risk factors of FMD injury, which provide potential value for timely prevention and treatment of cardiovascular diseases.