Usefulness of cervical root magnetic stimulation in assessing proximal motor nerve conduction

Diagnostic and prognostic significance of preoperative evoked potential tests in degenerative cervical myelopathy

BACKGROUND CONTEXT

Decompression surgery is a treatment option for patients with degenerative cervical myelopathy (DCM). Surgical decisions primarily depend on clinical symptoms and radiological examinations. The diagnostic and prognostic significance of evoked potential tests for surgical outcomes in patients with DCM has not been thoroughly examined.

PURPOSE

To identify the diagnostic and prognostic significance of preoperative evoked potential tests in patients with DCM who underwent decompression surgery.

STUDY DESIGN

This was a retrospective observational study.

PATIENT SAMPLE

One hundred two consecutive patients who underwent evoked potential tests and surgical treatment between January 2016 and December 2020 in a single spine center and had a minimum follow-up of 6 months.

OUTCOME MEASURES

Japanese Orthopedic Association (JOA) scores obtained preoperatively and 6 months after surgery.

METHODS

This study evaluated the preoperative central motor conduction time (CMCT), somatosensory evoked potentials, and Japanese Orthopedic Association (JOA) scores obtained preoperatively and 6 months after surgery.

RESULTS

Abnormal CMCT findings were observed in 94 patients (92.2%). Abnormal somatosensory evoked potentials were observed in 77 patients (75.5%). There was a statistically significant correlation between preoperative JOA score and abductor pollicis brevis (APB)-CMCT (r=-0.546, p=.001), tibialis anterior (TA)-CMCT (r=-0.517, p<.001), median nerve (MN)-SSEP (r=-0.353, p=.001), and tibial nerve (TN)-SSEP (r=-0.349, p=.003). There were significant differences in recovery rates associated with diabetes mellitus (DM), preoperative severity of myelopathy, TA-CMCT, MN-SSEP, and TN-SSEP. Stepwise multiple regression analysis showed that the major factors affecting the clinical outcomes were TN-SSEP (β=0.327, p=.004), preoperative JOA score (β=0.278, p=.012), and DM (β=0.241, p=.025).

CONCLUSIONS

Evoked potential testing is a functional diagnostic tool that can indicate the severity of myelopathic symptoms in patients with DCM. Additionally, preoperative TN-SSEP may have significant prognostic value in predicting postoperative clinical outcomes. Thus, preoperative evoked potential tests could be helpful for determining suitable surgical treatment candidates and forecasting postoperative prognosis.

Neurophysiological Evaluation of Neural Transmission in Brachial Plexus Motor Fibers with the Use of Magnetic versus Electrical Stimuli

The anatomical complexity of brachial plexus injury requires specialized in-depth diagnostics. The clinical examination should include clinical neurophysiology tests, especially with reference to the proximal part, with innovative devices used as sources of precise functional diagnostics. However, the principles and clinical usefulness of this technique are not fully described. The aim of this study was to reinvestigate the clinical usefulness of motor evoked potential (MEP) induced by a magnetic field applied over the vertebrae and at Erb's point to assess the neural transmission of brachial plexus motor fibers. Seventy-five volunteer subjects were randomly chosen to participate in the research. The clinical studies included an evaluation of the upper extremity sensory perception in dermatomes C5-C8 based on von Frey's tactile monofilament method, and proximal and distal muscle strength by Lovett's scale. Finally, 42 healthy people met the inclusion criteria. Magnetic and electrical stimuli were applied to assess the motor function of the peripheral nerves of the upper extremity and magnetic stimulus was applied to study the neural transmission from the C5-C8 spinal roots. The parameters of compound muscle action potential (CMAP) recorded during electroneurography and MEP induced by magnetic stimulation were analyzed. Because the conduction parameters for the groups of women and men were comparable, the final statistical analysis covered 84 tests. The parameters of the potentials generated by electrical stimulus were comparable to those of the potentials induced by magnetic impulse at Erb's point. The amplitude of the CMAP was significantly higher following electrical stimulation than that of the MEP following magnetic stimulation for all the examined nerves, in the range of 3-7%. The differences in the potential latency values evaluated in CMAP and MEP did not exceed 5%. The results show a significantly higher amplitude of potentials after stimulation of the cervical roots compared to potentials evoked at Erb's point (C5, C6 level). At the C8 level, the amplitude was lower than the potentials evoked at Erb's point, varying in the range of 9-16%. We conclude that magnetic field stimulation enables the recording of the supramaximal potential, similar to that evoked by an electric impulse, which is a novel result. Both types of excitation can be used interchangeably during an examination, which is essential for clinical application. Magnetic stimulation was painless in comparison with electrical stimulation according to the results of a pain visual analog scale (3 vs. 5.5 on average). MEP studies with advanced sensor technology allow evaluation of the proximal part of the peripheral motor pathway (between the cervical root level and Erb's point, and via trunks of the brachial plexus to the target muscles) following the application of stimulus over the vertebrae.

Translumbosacral Anorectal Magnetic Stimulation Test for Fecal Incontinence

BACKGROUND

Neuropathy may cause fecal incontinence and mixed fecal incontinence/constipation, but its prevalence is unclear, partly due to the lack of comprehensive testing of spino-anorectal innervation.

OBJECTIVE

This study aimed to develop and determine the clinical usefulness of a novel test, translumbosacral anorectal magnetic stimulation for fecal incontinence.

DESIGN

This observational cohort study was conducted from 2012 to 2018.

SETTINGS

This study was performed at a tertiary referral center.

PATIENTS

Patients with fecal incontinence, patients with mixed fecal incontinence/constipation, and healthy controls were included.

INTERVENTIONS

A translumbosacral anorectal magnetic stimulation test was performed by using an anorectal probe with 4 ring electrodes and magnetic coil, and by stimulating bilateral lumbar and sacral plexuses, uses and recording 8 motor-evoked potentials at anal and rectal sites.

MAIN OUTCOME MEASURES

The prevalence of lumbar and/or sacral neuropathy was examined. Secondary outcomes were correlation of neuropathy with anorectal sensorimotor function(s) and morphological changes.

RESULTS

We evaluated 220 patients: 144 with fecal incontinence, 76 with mixed fecal incontinence/constipation, and 31 healthy controls. All 8 lumbar and sacral motor-evoked potential latencies were significantly prolonged (p < 0.01) in fecal incontinence and mixed fecal incontinence/constipation groups compared with controls. Neuropathy was patchy and involved 4.0 (3.0) (median (interquartile range)) sites. Lumbar neuropathy was seen in 29% to 65% of the patients in the fecal incontinence group and 22% to 61% of the patients in the mixed fecal incontinence/constipation group, and sacral neuropathy was seen in 24% to 64% and 29% to 61% of these patients. Anal neuropathy was significantly more (p < 0.001) prevalent than rectal neuropathy in both groups. There was no correlation between motor-evoked potential latencies and anal sphincter pressures, rectal sensation, or anal sphincter defects.

LIMITATIONS

No comparative analysis with electromyography was performed.

CONCLUSION

Lumbar or sacral plexus neuropathy was detected in 40% to 75% of patients with fecal incontinence with a 2-fold greater prevalence at the anal region than the rectum. Lumbosacral neuropathy appears to be an independent mechanism in the pathogenesis of fecal incontinence, unassociated with other sensorimotor dysfunctions. Translumbosacral anorectal magnetic stimulation has a high yield and is a safe and clinically useful neurophysiological test. See Video Abstract at http://links.lww.com/DCR/B728.

PRUEBA DE ESTIMULACIN MAGNTICA TRANSLUMBOSACRAL ANORECTAL PARA LA INCONTINENCIA FECAL

ANTECEDENTES:La neuropatía puede causar incontinencia fecal y una combinación de incontinencia fe-cal/estreñimiento, pero su prevalencia no está clara, en parte debido a la falta de pruebas comple-tas de inervación espino-anorrectal.OBJETIVO:Desarrollar y determinar la utilidad clínica de una nueva prueba, estimulación magnética trans-lumbosacral anorrectal para la incontinencia fecal.DISEÑO:Estudio de cohorte observacional del 2012 al 2018.ENTORNO CLINICO:Centro de referencia terciario.PACIENTES:Pacientes con incontinencia fecal, combinación de incontinencia fecal/estreñimiento y controles sanos.INTERVENCIONES:Se realizó una prueba de estimulación magnética translumbosacral anorrectal utilizando una sonda anorrectal con 4 electrodos anulares y bobina magnética, y estimulando los plexos lumbares y sacros bilaterales y registrando ocho potenciales evocados motores las regiones anal y rectal.PRINCIPALES MEDIDAS DE RESULTADO:Se examinó la prevalencia de neuropatía lumbar y/o sacra. Los resultados secundarios fueron la correlación de la neuropatía con las funciones sensitivomotoras anorrectales y cambios morfológi-cos.RESULTADOS:Evaluamos 220 pacientes, 144 con incontinencia fecal, 76 con combinación de incontinencia fe-cal/estreñimiento y 31 sujetos sanos. Las ocho latencias de los potenciales evocadas motoras lum-bares y sacras se prolongaron significativamente (p <0,01) en la incontinencia fecal y el grupo mixto en comparación con los controles. La neuropatía fue irregular y afectaba 4,0 (3,0) (mediana (rango intercuartílico) sitios. Se observó neuropatía lumbar en 29-65% en la incontinencia fecal y 22-61% en el grupo mixto, y neuropatía sacra en 24-64% y 29-61 % de pacientes respectivamen-te. La neuropatía anal fue significativamente más prevalente (p <0,001) que la rectal en ambos grupos. No hubo correlación entre las latencias de los potenciales evocadas motoras y las presio-nes del esfínter anal, la sensación rectal o los defectos del esfínter anal.LIMITACIONES:Sin análisis comparativo con electromiografía.CONCLUSIÓNES:Se detectó neuropatía del plexo lumbar o sacro en el 40-75% de los pacientes con incontinencia fecal con una prevalencia dos veces mayor en la región anal que en el recto. La neuropatía lumbo-sacra parece ser un mecanismo independiente en la patogenia de la incontinencia fecal, no asocia-do con otras disfunciones sensitivomotoras. La estimulación magnética translumbosacral anorrec-tal tiene un alto rendimiento, es una prueba neurofisiológica segura y clínicamente útil. Consulte Video Resumen en http://links.lww.com/DCR/B728.

Excitatory and inhibitory responses to cervical root magnetic stimulation in healthy subjects

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We studied excitatory and inhibitory responses to cervical root magnetic stimulation.

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CRMS elicited direct and reflex responses in hand muscles.

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CRMS is painless and well tolerated and, therefore, applicable to clinical studies.

Objectives

To characterize direct and reflex hand muscle responses to cervical root magnetic stimulation (CRMS) in healthy volunteers during sustained voluntary contraction.

Methods

In 18 healthy volunteers, we recorded from the first dorsal interosseous (FDI) muscle the responses to CRMS of progressively increasing intensity and level of muscle contraction. The compound muscle action potential (CMAP) and the silent period (SP) were compared to those obtained with plexus, midarm and wrist stimulation. Additionally, in a smaller number of subjects, we obtained the peristimulus time histogram (psth) of single motor unit firing in the FDI, examined the effects of vibration and recorded the modulation of sustained EMG activity in muscles of the lower limbs.

Results

Increasing CRMS intensity led to larger CMAP with no relevant changes in SP1 or SP2, except for lower amplitude of the burst interrupting the silent period (BISP). Increasing the level of muscle contraction led to reduced CMAP, shorter SP duration and increased BISP amplitude. The psth analysis showed the underlying changes in the motor unit firing frequency that corresponded to the changes seen in the CMAP and the SP with surface recordings. Progressively distal stimulation led to CMAPs of shorter latency and increased amplitude, SPs of longer latency and shorter duration, and a BISP of longer latency. Vibration led to reduction of the SP. CRMS induced SPs in muscles of the lower limb.

Conclusions

CRMS induces excitatory and inhibitory responses in hand muscles, fitting with the expected behavior of mixed nerve stimulation at very proximal sites.

Significance

Characterization of the effects of CRMS on hand muscles is of physiological and potentially clinical applicability, as it is a painless and reliable procedure.

Cervical Spondylotic Myelopathy: Natural Course and the Value of Diagnostic Techniques -WFNS Spine Committee Recommendations

Objective

This study presents the results of a systematic literature review conducted to determine most up-to-date information on the natural outcome of cervical spondylotic myelopathy (CSM) and the most reliable diagnostic techniques.

Methods

A literature search was performed for articles published during the last 10 years.

Results

The natural course of patients with cervical stenosis and signs of myelopathy is quite variable. In patients with no symptoms, but significant stenosis, the risk of developing myelopathy with cervical stenosis is approximately 3% per year. Myelopathic signs are useful for the clinical diagnosis of CSM. However, they are not highly sensitive and may be absent in approximately one-fifth of patients with myelopathy. The electrophysiological tests to be used in CSM patients are motor evoked potential (MEP), spinal cord evoked potential, somatosensory evoked potential, and electromyography (EMG). The differential diagnosis of CSM from other neurological conditions can be accomplished by those tests. MEP and EMG monitoring are useful to reduce C5 root palsy during CSM surgery. Notable spinal cord T2 hyperintensity on cervical magnetic resonance imaging (MRI) is correlated with a worse outcome, whereas lighter signal changes may predict better outcomes. T1 hypointensity should be considered a sign of more advanced disease.

Conclusion

The natural course of CSM is quite variable. Signal changes on MRI and some electrophysiological tests are valuable adjuncts to diagnosis.

Standard neurophysiological studies and motor evoked potentials in evaluation of traumatic brachial plexus injuries - A brief review of the literature

PURPOSE

Traumatic damage to the brachial plexus is associated with temporary or permanent motor and sensory dysfunction of the upper extremity. It may lead to the severe disability of the patient, often excluded from the daily life activity. The pathomechanism of brachial plexus injury usually results from damage detected in structures taking origin in the rupture, stretching or cervical roots avulsion from the spinal cord. Often the complexity of traumatic brachial plexus injury requires a multidisciplinary diagnostic process including clinical evaluation supplemented with clinical neurophysiology methods assessing the functional state of its structures. Their presentation is the primary goal of this paper.

METHODS

The basis for the diagnosis of brachial plexus function is a clinical examination and neurophysiology studies: electroneurography (ENG), needle electromyography (EMG), somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) assessing the function of individual brachial plexus elements.

CONCLUSIONS

The ENG and EMG studies clarify the level of brachial plexus damage, its type and severity, mainly using the Seddon clinical classification. In contrast to F-wave studies, the use of the MEPs in the evaluation of traumatic brachial plexus injury provides valuable information about the function of its proximal part. MEPs study may be an additional diagnostic in confirming the location and extent of the lesion, considering the pathomechanism of the damage. Clinical neurophysiology studies are the basis for determining the appropriate therapeutic program, including choice of conservative or reconstructive surgery which results are verified in prospective studies.

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

PURPOSE

To identify and compare the features of compound muscle action potential (CMAP) decrements in repetitive nerve stimulation (RNS) in patients with cervical spondylotic amyotrophy (CSA) and in patients with amyotrophic lateral sclerosis (ALS).

METHODS

The cohort consisted of 43 CSA (distal-type to proximal-type ratio: 27-16) and 35 ALS patients. Five muscles, including abductor pollicis brevis (APB), abductor digiti minimi (ADM), biceps brachii (BB), middle deltoid (Del), and upper trapezius (Trap), were tested by 3-Hz RNS. Decrements greater than cutoff values (APB > 5.8%; ADM > 4.8%; BB > 5.2%; Del > 6%; Trap > 5.1%) determined using receiver operating characteristic (ROC) curves were defined as abnormal, and the conventional criterion (≥10%) was also considered.

RESULTS

A significant CMAP decrement (>cutoff values) was recorded from at least one tested muscle in 91.4% of ALS patients, and was most common in the proximal muscle, a finding that differed significantly from CSA patients (32.6%, P < 0.05). The application of cutoff values greatly improved the sensitivity of RNS over the conventional criterion (≥10%) for the detection of ALS (P < 0.05). The specificity of this technique remained higher when performing RNS in the proximal muscles, especially in the upper trapezius (AUC = 0.864, sensitivity = 0.643, and specificity = 1.000). The decrement percentages were significantly greater in the proximal muscles of ALS patients than in those of the CSA patients (P < 0.05). In addition, illness duration was not correlated with decrement percentage in either patient group, and no difference in the frequency of decrement among different ALS diagnostic categories was observed (P > 0.05).

CONCLUSIONS

The application of RNS, especially in proximal muscles, may provide a simple accurate and noninvasive supplementary test for distinguishing CSA from ALS, even in the early stage of these diseases. A combination of RNS, needle EMG, clinical features and cervical magnetic resonance imaging may yield sufficient diagnostic information to differentiate CSA and ALS.