A comparison of magnetic and electrical stimulation of spinal nerves

Effectiveness of Magnetic Stimulation in the Treatment of Urinary Incontinence: A Systematic Review and Results of Our Study

Urinary incontinence (UI) is becoming an increasingly common health problem. UI treatment can be conservative or surgical. This paper focuses on the effectiveness of magnetic stimulation (MS) in the treatment of UI. We performed a systematic review in order to combine and compare results with results from our clinical study. A clinical prospective non-randomized study was carried out at the Ljubljana University Medical Center's Gynecology Division. It included 82 randomly selected female patients, irrespective of their UI type. The success rate of using MS in treating UI was based on standardized ICIQ-UI SF questionnaires. Patients completed 10 therapy sessions on MS, and follow-up was performed 3 months after the last therapy session. UI improved after treatment with MS. The ICIQ-UI SF score improved in patients regardless of the type of UI. However, the greatest decrease in post-treatment assessment ICIQ-UI SF scores was seen in patients with stress urinary incontinence (SUI). Based on the findings described above, it can be concluded that MS is a successful non-invasive conservative method for treating UI. Future studies are necessary, all of which should include a large sample size, a control group, an optimal research protocol, pre-treatment analyses, standardization, and longer follow-ups.

Evaluation of proximal and distal motor nerve conduction using the electrical root stimulation technique in the femoral and obturator nerves

Objectives: This study aimed to investigate the adaptability of the electrical root stimulation technique by achieving normative data from the obturator and femoral nerves of healthy dogs.

Methods: For this purpose, two stimulations and recordings were performed on both the obturator and femoral nerves in 40 dogs (22 males and 18 females). Electrical root stimulation was applied via monopolar needle electrodes between the sixth to seventh and fifth to sixth lumbar inter arcuate spaces to the obturator and femoral nerves, respectively. Muscle waves were recorded from the gracilis and sartorius muscles of the left and right pelvic limb.

Results: The proximal motor nerve conduction velocity was 60.89 ± 3.93 m/s and 59.87 ± 4.83 m/s in the obturator and femoral nerves, respectively.

Clinical significance: Our results showed that electrical root stimulation could be a useful method to test the integrity of the roots of obturator and femoral nerves and their proximal parts.

The therapeutic efficiency of extracorporeal magnetic innervation treatment in women with urinary tract dysfunction following radical hysterectomy

Data on 32 consecutive women with demonstrable urinary tract dysfunction for at least 6 months following radical hysterectomy (RH) for uterine cervical cancer, who received 24 sessions of extracorporeal magnetic innervation (ExMI) treatment twice-weekly were collected. The 1-h pad test weight decreased from 27.2 g pre-treatment to 12.1 g post-treatment (p < 0.05). Both the median UDI-6 and IIQ-7 scores showed statistically significant improvements (p < 0.001) at every stage of the ExMI treatment and in the 24.2 months mean follow-up duration after treatment. The symptoms of frequency, stress incontinence, urge incontinence and voiding difficulty showed statistically significant improvements (p < 0.001) after 8 and 24 sessions of ExMI treatment. The urodynamic parameters between pre-treatment and post-treatment after 24 sessions revealed no statistically significant changes. Based on the objective and subjective measures observed in this study, 24 sessions of twice-weekly ExMI treatment is an additional non-invasive therapy option for patients with the symptoms of lower urinary tract following RH.

Electrical stimulation of lumbar spinal nerve roots in dogs

The aim of this study was to test the applicability of electrical stimulation of lumbar spinal nerve roots and obtain normative electrical root stimulation (ERS) data for L7 nerve root and sciatic nerve in dogs. For that purpose ERS and sciatic nerve stimulations were performed consecutively, in totally 40 healthy dogs. ERS was applied in the L7/S1 intervertebral space via monopolar needle electrodes. Muscle responses were recorded from the gastrocnemius muscles on the left and right hind limbs. Sciatic nerve stimulation was performed at the greater trochanter level on the left hind limb, with records obtained from the left gastrocnemius muscle. Mean root latencies of the left and right side were 5.22 ± 0.49 ms and 5.29 ± 0.53 ms, respectively. There was no significant difference in root latency between the right and left sides. The mean terminal latency was 3.82 ± 0.46 ms. The proximal motor nerve conduction velocity of the sciatic nerve was 63.15 ± 3.43 m/s. The results of this study show that ERS provides objective data about the integrity of lumbar spinal nerve roots by evaluating the entire population of motor fibres and total length of the motor axon in dogs. ERS can be considered a useful diagnostic method for confirmation of diagnoses of lumbosacral diseases.

Can Extracorporeal Magnetic Innervation Be a Treatment Modality for Primary Dysmenorrhea

<b><i>Background/Aims:</i></b> To evaluate the efficacy of extracorporeal magnetic innervation (ExMI) as a treatment for primary dysmenorrhea compared with nonsteroidal anti-inflammatory drugs (NSAIDs) and combined oral contraceptives (COCs). <b><i>Methods:</i></b> The cases were randomized into three groups (NSAID = 51, ExMI = 53, COC = 54). ExMI was applied for a total of 10 sessions. Women in the NSAID group used an oral NSAID at the start of each menstruation. Women in the COC group were given combined pills. Of the treatment options, ExMI was applied for only a single period, whereas NSAID and COC use continued for 12 months. <b><i>Results:</i></b> At the first menstruation, visual analog scale (VAS) scores improved significantly in all groups (p < 0.001). NSAIDs and COCs continued to show efficacy over the entire study period (p < 0.05). However, in the ExMI group, VAS values increased from the first menstruation until 12 months. The VAS score at the 12th month was significantly higher in the ExMI group than in the other groups (p < 0.05), but markedly lower than the pretreatment value (49.9 ± 8.3 vs. 71.1 ± 10.1, p < 0.001). <b><i>Conclusions:</i></b> ExMI therapy might be a promising novel noninvasive option for primary dysmenorrhea. Efficacy began to decline after 3 months, but continued for 12 months.

A methodological reappraisal of non invasive high voltage electrical stimulation of lumbosacral nerve roots

OBJECTIVE

To describe a neurophysiological method to locate the optimal stimulation site (OSS) over the vertebral column, customized to the individual subject, to achieve maximal activation of lumbosacral roots by means of non-invasive high voltage electrical stimulation (HVES).

METHODS

OSS was located in 30 volunteers by testing different stimulation points of a surface multi-electrode array placed over the dorso-lumbar junction of the vertebral column. The dorso-ventral stimulating montage was used (Troni et al., 1996). Motor responses to root stimulation (rCMAPs) were bilaterally recorded from Vastus Medialis (VM), Tibialis Anterior (TA), Soleus (SL) and Flexor Hallucis Brevis (FHB) muscles. The direct nature of rCMAPs was tested by delivering two maximal stimuli 50 ms apart.

RESULTS

Except for a few subjects with large girth, maximal rCMAPs could be obtained from all muscles with a stimulating current intensity up to 550 V (1050 mA). Maximal double HVES excluded any reflex component in the recorded rCMAPs. The procedure was well tolerated and no side effects were observed.

CONCLUSIONS

A single maximal electric shock delivered at the proper vertebral level by means of the dorso-ventral montage is able to safely achieve synchronous, bilateral maximal activation of several roots, from L3 to S1.

SIGNIFICANCE

Maximal activation of lumbosacral roots at their origin, unattainable with magnetic stimulation, is the essential requirement for direct detection of proximal nerve conduction slowing and block in lower limbs.

The use of extracorporeal magnetic innervation for the treatment of stress urinary incontinence in older women: a pilot study

PURPOSE

Stress urinary incontinence (SUI) is a major health problem that has substantial and important effects on health-related quality of life. In recent years, extracorporeal magnetic innervation (ExMI) has become a preferred method of treatment in urinary incontinence. This study presents the effects of ExMI treatment on pelvic floor muscle strength, urinary symptoms, incontinence conditions and quality of life of older women with SUI.

METHODS

A total of 13 patients between the ages of 61 and 69 (mean 65.23 ± 2.8 years) were treated for SUI with ExMI. The following parameters were investigated: urinary symptoms, pelvic floor electromyographic (EMG) activity, 1-h pad test, incontinence conditions utilizing visual analog scale (VAS) and quality of life using Turkish version of the Urogenital Distress Inventory (UDI-6) and the Incontinence Quality of Life Instrument (I-QoL). All assessments were conducted at baseline and at the end of the study. Treatment lasted for 20 min, twice a week and for a total of 6 weeks.

RESULTS

The urinary symptoms and incontinence conditions decreased after the ExMI treatment sessions. The pad test results indicated a reduction in urine loss (p = 0.016). EMG values were improved (p = 0.005). Scores of I-QoL, UDI-6 and VAS were reduced after the treatment, respectively (p = 0.002), (p = 0.002) and (p = 0.006).

CONCLUSION

Extracorporeal magnetic innervation can be considered as it is an alternative, non-invasive and painless treatment method with good compliance for treatment of SUI in older patients.

Neurophysiological study to assess the severity of each site through the motor neuron fiber in entrapment neuropathy

Background

The double crush hypothesis (DCH) that had been widely accepted seems to have been dismissed recently. Prior to the DCH, retrograde changes in the proximal median nerve in carpal tunnel syndrome (CTS) were reported. There has been no report of quantitative analyzing about the effect of one site's compression on another site all through the same peripheral nerve in CTS patients.

Methods

We measured the central motor conduction time (CMCT), motor conduction latency of the cervical root region (CRL), peripheral path latency from the rootlet to the wrist (PL) and motor distal latency (MDL) in the median nerve and ulnar nerves, respectively in CTS patients.

Results

MDL, PL and CRL were prolonged selectively in the median nerve, but not in the ulnar nerve of CTS patients. And in the median nerve measurement, MDL was high (r = 0.59, p < 0.0001) while PL showed a significant (r = -0.28, p < 0.05) relationship with CRL. MDL was large (r = 0.58, p < 0.0001) and showed a close (r = 0.59, p < 0.0001) relationship with the amplitude of CMAP. There was no significant difference between the amplitude of the normal CRL group and that of the prolonged CRL group. This quantitative analysis showed a linear relationship among MDL, CRL and CMAP amplitude.

Conclusion

Dual entrapment lesions did not unexpectedly exaggerate the vulnerability or total damage. The vulnerability and the damage were proportional to the severity of each lesion. If the DCH term presented to an unexpectedly exaggerated degree, the cases of double crush symdrome in the CTS patients were rare, but if the term DCH refers to only this linear relationship, the DCH should not be dismissed.

Proximal femoral conductions in patients with lumbosacral radiculoplexus neuropathy

OBJECTIVES

Lumbosacral radiculoplexus neuropathy (DLRPN) is a rare form of neuropathy observed in diabetic and rarely non-diabetic patients. Pathophysiology and lesion location are not clearly understood. Our aim was to analyze proximal and distal femoral conductions in patients with DLRPN.

METHODS

Six patients with DLRPN, 14 patients with diabetic polyneuropathy and 25 healthy subjects were included in the study. We performed L3 monopolar root stimulation and femoral nerve trunk stimulation at the inguinal region and calculated lumbar plexus conduction time by subtracting the latency of compound muscle action potential (CMAP) of the vastus medialis evoked by femoral nerve stimulation from the latency of CMAP of vastus medialis evoked by L3 root stimulation. Additionally peak to peak amplitudes and areas of CMAPs were analyzed.

RESULTS

Electrophysiological examination showed that there was an axonal involvement in all patients with DLRPN. Prolonged lumbar plexus conduction time (in five extremities), and prolonged distal latency of the femoral nerve (in five extremities) probably due to secondary demyelination were also observed. Similar abnormalities were not observed in the diabetic polyneuropathy group.

CONCLUSIONS

DLRPN may affect different localizations on the peripheral nerves. L3 root stimulation may have an important role in the electrodiagnosis of DLRPN.

Optimal arrangement of magnetic coils for functional magnetic stimulation of the inspiratory muscles in dogs

In an attempt to maximize inspiratory pressure and volume, the optimal position of a single or of dual magnetic coils during functional magnetic stimulation (FMS) of the inspiratory muscles was evaluated in twenty-three dogs. Unilateral phrenic magnetic stimulation (UPMS) or bilateral phrenic magnetic stimulation (BPMS), posterior cervical magnetic stimulation (PCMS), anterior cervical magnetic stimulation (ACMS) as well as a combination of PCMS and ACMS were performed. Trans-diaphragmatic pressure (Pdi), flow, and lung volume changes with an open airway were measured. Transdiaphragmatic pressure was also measured with an occluded airway. Changes in inspiratory parameters during FMS were compared with 1) electrical stimulation of surgically exposed bilateral phrenic nerves (BPES) and 2) ventral root electrical stimulation at C5-C7 (VRES C5-C7). Relative to the Pdi generated by BPES of 36.3 +/- 4.5 cm H2O (Mean +/- SEM), occluded Pdi(s) produced by UPMS, BPMS, PCMS, ACMS, and a combined PCMS + ACMS were 51.7%, 61.5%, 22.4%, 100.3%, and 104.5% of the maximal Pdi, respectively. Pdi(s) produced by UPMS, BPMS, PCMS, ACMS, and combined ACMS + PCMS were 38.0%, 45.2%, 16.5%, 73.8%, and 76.8%, respectively, of the Pdi induced by VRES (C5-C7) (48.0 +/- 3.9 cm H2O). The maximal Pdi(s) generated during ACMS and combined PCMS + ACMS were higher than the maximal Pdi(s) generated during UPMS, BPMS, or PCMS (p < 0.05). ACMS alone induced 129.8% of the inspiratory flow (73.0 +/- 9.4 L/ min) and 77.5% of the volume (626 +/- 556 ml) induced by BPES. ACMS and combined PCMS + ACMS produce a greater inspiratory pressure than UPMS, BPMS or PCMS. ACMS can be used to generate sufficient inspiratory pressure, flow, and volume for activation of the inspiratory muscles.

Extracorporeal magnetic innervation treatment for urinary incontinence

BACKGROUND

Extracorporeal magnetic innervation (ExMI) is a new technology used for pelvic muscle strengthening for the treatment of stress urinary incontinence. We explored whether this new technology is effective for patients with urge incontinence, as well as those with stress urinary incontinence.

METHODS

We studied 20 patients with urge incontinence and 17 patients with stress urinary incontinence. The Neocontrol system (Neotonus Inc., Marietta, GA) was used. Treatment sessions were for 20 min, twice a week for 8 weeks. Evaluations were performed by bladder diaries, one-hour pad weight testing, quality-of-life surveys and urodynamic studies.

RESULTS

Of the urge incontinence cases, five patients were cured (25.0%), 12 patients improved (60.0%) and three patients did not show any improvement (15.0%). Leak episodes per day reduced from 5.6 times to 1.9 times at 8 weeks (P < 0.05). Eight patients with urge incontinence recurred within 24 weeks after the last treatment (47.1%). Of the stress incontinence cases, nine patients were cured (52.9%), seven patients improved (41.1%) and one patient did not show any improvement (6%). In one-hour pad weight testing, the mean pad weight reduced from 7.9 g to 1.9 g at 8 weeks (P < 0.05). Three patients returned to the baseline values within 24 weeks after the last treatment (17.6%). No side-effects were experienced by any of the patients.

CONCLUSION

Although the results for urge incontinence were less effective than for stress urinary incontinence, ExMI therapy offers a new option for urge incontinence as well as stress urinary incontinence.

Electrodiagnosis of neck pain

The past 3 decades have witnessed tremendous advances in the field of electrodiagnostic medicine. The high-performance electronics and microprocessors available in contemporary electrodiagnostic instruments have improved the ability to detect, record, measure, and interpret the action potentials arising from the nerves and muscle fibers. With their increased ease of use and effectiveness in both diagnosis and prognosis, electrodiagnostic tests have become valuable tools in evaluation of patients with neck pain. As with any laboratory measure, the utility of electrodiagnostic testing can be increased when it is used in appropriate clinical contexts and when its limitations are understood.

Proximal nerve conduction by high-voltage electrical stimulation in S1 radiculopathies and acquired demyelinating neuropathies

OBJECTIVE

To evaluate the reliability and sensitivity of the high-voltage electrical stimulation for studying proximal conduction of peripheral motor axons in normal subjects, S(1) radiculopathies and acquired demyelinating neuropathies.

METHODS

Twelve patients with compressive S(1) radiculopathy, 22 patients with acquired demyelinating neuropathy and 29 healthy volunteers were examined. The conduction of peripheral motor axons between lumbosacral roots and the sciatic nerve at the gluteal fold was investigated by high-voltage electrical stimulation delivered percutaneously.

RESULTS

The main electrophysiological finding in S(1) radiculopathy was an abnormal side to side difference in the amplitude of the compound motor action potential by proximal stimulation. Overall, the frequency of abnormalities detected by using high-voltage electrical stimulation was similar to that found with conventional EMG studies, and the two methods showed electrophysiological alterations in the same patients. In all patients with acquired demyelinating neuropathy, the proximal motor nerve conduction velocity from lumbosacral roots to the sciatic nerve at the gluteal fold was reduced; proximal stimulation of the motor axons revealed electrophysiological abnormalities more often than when using other electrophysiological techniques (F wave and H reflex).

CONCLUSIONS

High-voltage electrical stimulation of peripheral motor axons shows high sensitivity in detecting proximal neuropathies; it can also define the site and relevance of proximal lesions in the peripheral nervous system better than other conventional techniques.

Electrophysiological evaluation of conduction in the most proximal motor root segment

Root conduction time (RCT), defined as the time difference between M-wave latency by cervical magnetic stimulation (CMS) and the total peripheral motor conduction time calculated from the shortest F-wave latency, was investigated in patients with inflammatory demyelinating neuropathies (IDP) and amyotrophic lateral sclerosis (ALS). The minimal threshold for CMS also was studied. In the IDP patients, conduction in the proximal motor root segment was considered abnormal in 52% by the RCT and in 47% by the minimal threshold for CMS, whereas both were normal in 85% of the ALS patients. These findings suggest that the RCT and minimal threshold for CMS might be additional parameters for evaluating motor nerve conduction in IDP.

Diagnostic value of electrical stimulation of lumbosacral roots in lumbar spinal stenosis

OBJECTIVES

This paper compares the diagnostic sensitivity of two tests in lumbar spinal stenosis (LSS): lumbosacral root stimulation with needle electrodes and needle electromyograph (EMG).

MATERIAL AND METHODS

Twenty patients with LSS were assigned to two groups: Patients with 'neurogenic intermittent claudication' (NIC) only (n=11), and patients with 'neurological signs' (n=9). Ten normal subjects were also examined. The effects of direct stimulation of the lumbosacral roots and conventional EMG recorded from important muscles [rectus femoris (RF): L4, tibialis anterior (TA): L5, soleus muscle (SOL): S1], were compared with each other and correlated with their respective clinical findings and radiological images.

RESULTS

Needle EMG and nerve conduction study revealed pathology in 15/20 patients, and electrical stimulation of the roots in 17/20 patients. Agreement in radiological findings with electrical stimulation of the roots and EMG was found in 12 patients. The other patients were harmonic with radiological findings either in EMG or in electrical stimulation of the roots.

CONCLUSIONS

Electrical root stimulation revealed more abnormalities in patients with LSS in comparison with needle EMG. However, both methods seemed to complement each other to show additional pathology in a given patient.

Electrophysiology of radiculopathies

The anatomy, pathophysiology, and clinical evaluation of radiculopathies are discussed. Defining whether root injury is present and which roots are involved can be difficult but critical for patient management. In conjunction with clinical and radiological information, studies that establish physiological abnormalities of roots should be helpful and important. Clinical neurophysiological studies for radiculopathies are performed frequently but have yet to achieve a universally accepted role in the evaluation of these patients. Electrophysiological techniques for the evaluation of radiculopathies are reviewed. Needle electromyography is the best established of these procedures but has the disadvantage of requiring injury to motor fibers of both a certain degree and distribution. Nerve conduction studies may rarely be abnormal in radiculopathies but are needed to be certain other conditions that may produce similar symptoms and signs are not present. H reflexes and F waves probably have roles in the evaluation of radiculopathies but published reports about F waves in radiculopathies have been marred by inadequate methodology. There is evidence based on large series of patients that somatosensory evoked potentials can be helpful for evaluating patients with multilevel injury such as spinal stenosis, patients where electrophysiological studies may have their greatest clinical utility. Further work using either electrical stimulation with needles or magnetic stimulation of roots seems warranted. The demonstration of meaningful electrophysiological changes with activities that reproduce radicular symptoms may be a promising experimental approach. Available information does not necessarily answer critical questions about the role of electrophysiology in patients with radiculopathies. This cannot be done using analyses based on current ideas about evidence based medicine given the absence of a 'gold standard' for defining radiculopathies as well the absence of blinded studies. The available information provides strong arguments for further investigations evaluating different clinical neurophysiological techniques in the same patient, and for evaluating the value of these techniques by concentrating on their clinical import.

N10 potential as an antidromic motor evoked potential in a median nerve short-latency somatosensory evoked potential study

When stimulating the mixed nerve to record evoked potential, both sensory and motor fibers are activated before entering the spinal cord. The N10 potential has been described as an antidromic motor evoked potential based on results obtained by recording at the anterior midneck. In the present study, we examined the changes in latencies of Erb's potential, N10, and N13 by stimulating the median nerve distally at the wrist and proximally at the elbow. The conduction velocity of N10 calculated by the difference between N10 latencies at the two stimulation points was consistent with motor conduction velocity, although N13 conduction velocity estimated by the same method reflected a sensory conduction velocity. A positive relation was also observed between the indirect latency from the stimulation point to the anterior root as calculated using the equation (F - M - 1) / 2 (ms) and the direct latency to the negative peak of the N10 potential. Our data support the notion that N10 represents antidromic motor potential originating in the spinal entry zone of the anterior root.

Proximal motor conduction evaluated by transcranial magnetic stimulation in acquired inflammatory demyelinating neuropathies

OBJECTIVES

To evaluate conduction abnormalities in the proximal motor nerve in patients with acquired inflammatory demyelinating neuropathies by transcranial magnetic stimulation (TMS).

METHODS

TMS intensity and background voluntary contraction (BVC) to evoke maximal size of motor evoked potential (MEP) in hand muscle were investigated in 24 normal subjects. Effect of experimentally induced conduction block by injecting local anesthetics in the peripheral nerve on MEP size was also studied in two normal subjects. In 22 patients with inflammatory demyelinating neuropathies, maximal MEPs were recorded in the deteriorating and recovery stages of the illness.

RESULTS

In normal subjects, the MEP became maximal with 30-50% of maximal BVC and at more than 80% the maximal stimulator output of the 2.0 T circular coil. The change in MEP size well reflected the degree of conduction block induced by local anesthetics. Findings for patients suggested conduction abnormalities proximal to axilla in 9 patients, and that the abnormal reduction of Erb CMAP was the result of submaximal stimulation, not true conduction block, in 3 patients. The increase in MEP/wrist CMAP ratio was better correlated with improvement in muscle strength than with change in the axilla or Erb CMAP/wrist CMAP ratio.

CONCLUSIONS

Problems such as conduction abnormalities in the motor tract of the central nervous system could not fully be excluded, but we consider that maximal MEP size can be used to predict proximal motor nerve conduction abnormalities.

Comparative study of the effects of magnetic versus electrical stimulation on inhibition of detrusor overactivity

OBJECTIVES

To perform a randomized comparative study investigating the urodynamic effects of functional magnetic stimulation (FMS) and functional electrical stimulation (FES) on the inhibition of detrusor overactivity.

METHODS

Thirty-two patients with urinary incontinence due to detrusor overactivity (15 men, 17 women; age 62. 3 +/- 16.6 years) were randomly assigned to two treatment groups (15 patients in the FMS group and 17 in the FES group). Stimulation was applied continuously at 10 Hz in both groups. For FMS, the magnetic stimulator unit was set on an armchair type seat and had a concave-shaped coil, so that the patients could sit during stimulation. For FES, a vaginal electrode was used in the women and a surface electrode on the dorsal part of the penis was used in the men. Cystometry was performed before and during the stimulation.

RESULTS

The bladder capacity at the first desire to void and the maximum cystometric capacity increased significantly during stimulation compared with prestimulation levels in both groups (P = 0.0054 and 0.0026, respectively, in the FMS group and P = 0.0015 and 0.0229, respectively, in the FES group). However, the increase in the maximum cystometric capacity was significantly (P = 0.0135) greater in the FMS group (114.2 +/- 124.1 mL or an increase of 105. 5% +/- 130.4% compared with the pretreatment level) than that in the FES group (32.3 +/- 56.6 mL or an increase of 16.3% +/- 33.9%). Detrusor overactivity was abolished in 3 patients in the FMS group but not in any patient in the FES group.

CONCLUSIONS

Although both treatments were effective, the inhibition of detrusor overactivity appeared greater in the FMS group than in the FES group.

Induction of urethral closure and inhibition of bladder contraction by continuous magnetic stimulation

Magnetic stimulation has been considered to be a technique for stimulating nervous system noninvasively and it has been used for experimental and clinical testings on the central and peripheral nervous systems. However, commercially available magnetic stimulators can only discharge single pulses for less than several minutes because the coil soon overheats. We newly devised a continuous magnetic stimulator assuring long-time stimulation, and this study was designed to confirm whether continuous magnetic stimulation would result in urethral closure and inhibition of bladder contraction in anesthetized canine models. Twelve female beagle dogs, weighing 9 to 12 kg, were anesthetized with a mixture of alpha-chloralose and urethane. In six beagles, a 4 F microtip transducer was inserted transurethrally, and maximum intraurethral pressure was monitored. In the remaining six animals, urethra was ligated at the bladder neck and a 4 F double lumen catheter was inserted from the dome of the bladder to infuse physiological saline, monitoring iso-volumetric rhythmic bladder contraction. The stimulating coil, of which temperature was kept at 20-25 degrees C by the built-in cooling system, was placed on the ishio-rectal fossa to stimulate the pudendal nerve at 10 Hz. The intraurethral pressure increased by 69.1 +/- 27.8 cm H(2)O, and iso-volumetric rhythmic bladder contraction was inhibited during the stimulation with 80% (240 Joule) of maximum output. In conclusion, continuous magnetic stimulator was found effective for urethral closure and inhibition of bladder contraction. Neurourol. Urodynam. 18:505-510, 1999.

Stimulation of peripheral nerves using a novel magnetic coil

Magnetic nerve stimulation (MNS) using a novel figure-8 magnetic coil was compared with conventional electric nerve stimulation (ENS) in normal subjects and in patients with disorders of the peripheral nervous system. In contrast to previously tested coils, the virtual cathode of the novel coil was independent of the geometrical or electric conditions of the stimulated tissue. Maximal compound muscle action potentials (CMAPs) were elicited by MNS in all motor nerves tested. The slopes of the recruitment curves of ENS were steeper than those of MNS, indicating a comparatively lower maximal stimulation intensity and a higher intensity resolution of the magnetic stimulator. In four patients with entrapment syndromes at the ulnar groove, motor conduction velocities and amplitudes were similar for MNS and ENS across the affected nerve segment. However, in two patients with chronic inflammatory demyelinating polyneuropathy (CIDP), CMAPs were slightly smaller following MNS. This new technique is a promising step toward the ultimate goal of replacing ENS with MNS.

Clinical neurophysiologic studies: which test is useful and when?

Neurophysiological studies test the integrity of nerve roots and nerves at different points from the spinal cord to the periphery. EMG is the most sensitive neurophysiological test for evaluating patients with radiculopathy, providing information on diagnosis, location, and prognosis. F-wave and H-reflex studies may be abnormal, but the information that they provide is nonspecific and usually redundant because the needle examination is abnormal anyway. Somatosensory evoked potentials are less sensitive and specific than EMG for diagnosing a radiculopathy, but uncommonly may be the only abnormality. Magnetic stimulation, paraspinal mapping, and cervical root stimulation are investigational techniques of uncertain utility.

AAEM minimonograph 32: the electrodiagnostic examination in patients with radiculopathies. American Association of Electrodiagnostic Medicine

The anatomy and pathophysiology of radiculopathies are reviewed, and the electrodiagnostic approaches used in evaluating patients with suspected root lesions are discussed. Such electrophysiologic procedures include motor and sensory nerve conduction studies, late-response studies, somatosensory and motor evoked potentials, nerve root stimulation, and needle electromyography. The value and limitations of these different procedures are considered. At the present time, needle electromyography is the single most useful approach. The findings in patients with radiculopathies at different levels are summarized.

Central motor conduction time: reproducibility and discomfort of different methods

Central motor conduction time, a useful measure for studying central motor pathways, is calculated by determining the difference between the latency of motor-evoked potentials and peripheral conduction time. The intraindividual trial-to-trial variability of central motor conduction time and the discomfort associated with three methods of measuring peripheral motor conduction time (F-wave latency, cervical magnetic stimulation, and cervical needle stimulation) were studied in 5 healthy subjects with the use of transcranial magnetic stimulation to elicit motor-evoked potentials. Central motor conduction time was calculated by using measurements, made on 3 separate days, from the same three muscles on each hand. A visual analog pain scale was used to determine the level of discomfort for each method. Intraindividual trial-to-trial variability of central motor conduction time was similar for all methods, with coefficients of variation of 13% for the F-wave latency, 15% for cervical magnetic stimulation, and 11% for cervical needle stimulation. The last method was significantly more painful than the other two methods; there was no significant difference in discomfort between the F-wave method and cervical magnetic stimulation. To assess peripheral motor conduction time, when determining central motor conduction time, either the F-wave method or cervical magnetic stimulation is preferable to cervical needle stimulation.

Functional magnetic stimulation of the respiratory muscles in dogs

This study assessed the ability of functional magnetic stimulation (FMS) to activate the respiratory muscles in dogs. With the animal supine, FMS of the phrenic nerves using a high-speed magnetic stimulator was performed by placing a round magnetic coil (MC) at the carotid triangle. Following hyperventilation-induced apnea, changes in volume (deltaV) and airway pressure (deltaP) against an occluded airway were determined. FMS of the phrenic nerves produced substantial inspired function (deltaV = 373 +/- 20.5 mL and deltaP = -20 +/- 2.0 cm H2O). After bilateral phrenectomies, maximal inspired deltaV (219 +/- 12.2 mL) and deltaP (-10 +/- 1.0 cm H2O) were produced when the MC was placed near the C6-C7 spinous processes, while maximal expired deltaV (-199 +/- 22.5 mL) and deltaP (11 +/- 2.3 cm H2O) were produced following stimulation near the T9-T10 spinous processes. We conclude: (1) FMS of either the phrenic or upper intercostal nerves results in inspired volume production; (2) FMS of the lower intercostal nerves generates expired volume production; and (3) FMS of the respiratory muscles may be a useful noninvasive tool for artificial ventilation and assisted cough in patients with spinal cord injuries or other neurological disorders.

Improved methodology for lumbosacral nerve root stimulation

The site of S1-S2 root activation following percutaneous high-voltage electrical (ES) and magnetic stimulation were located by analyzing the variations of the time interval from M to H soleus responses elicited by moving the stimulus point from lumbar to low thoracic levels. ES was effective in activating S1-S2 roots at their origin. However supramaximal motor root stimulation required a dorsoventral montage, the anode being a large, circular surface electrode placed ventrally, midline between the apex of the xiphoid process and the umbilicus. Responses to magnetic stimuli always resulted from the activation of a fraction of the fiber pool, sometimes limited to the low-thresholds afferent component, near its exit from the intervertebral foramina, or even more distally. Normal values for conduction velocity in motor and 1a afferent fibers in the proximal nerve tract are provided.

Comparison of various coils used for magnetic stimulation of peripheral motor nerves: physiological considerations and consequences for diagnostic use

We compared the ability of 4 magnetic coils to activate peripheral nerves in healthy subjects. No differences in motor threshold intensities were found between the coils, but the intensities needed to elicit maximum compound muscle action potential (CMAP) amplitudes were different. For superficial nerves maximum CMAPs in comparison with electrical stimulation were usually but not always found. CMAPs were at their maximum only when the direction of induced current flowed from proximal to distal and when a certain part of the coil was over the nerve. Distal nerve stimulation was time consuming. Due to artifacts many stimuli were necessary and sometimes no maximum CMAP could be elicited. CMAPs were much less sensitive to position changes of the coil than to changes in an electrical stimulator. Small circular coils were superior to larger coils in terms of the lower intensities necessary to elicit maximum CMAPs, better focusing of the stimulus, and less artifacts. For deep nerves amplitudes were always submaximal. Coactivation of nearby nerves and underlying muscles was another main drawback especially at proximal sites and for coils of large diameter. Despite better focusing, double coils are less useful due to their great diameter. Magnetic stimulation cannot replace electrical neurography at the moment, even if different coils are used at different sites of stimulation.

[Somesthetic evoked potentials and serial motor evoked potentials in the study of proximal peripheral nerve conduction. Apropos of 7 cases]

The study of proximal motor and sensory nerve conduction in the thoracic outlet syndrome is still difficult and laborious in 1994. However, these conductions can be measured at different levels by means of somaesthetic evoked potentials and motor evoked potentials, when one takes the time to perform them. The study in normal subjects demonstrates that the proximal sensory and motor conduction delays are approximately 3.2 ms and are therefore comparable to that of the median nerve at the wrist. The study of 7 cases related to various diseases shows that these techniques, performed after electromyogram of both upper limbs, an essential prerequisite to their interpretation, are able to clearly demonstrate abnormalities of proximal conduction in patients suffering from of a scalene syndrome, a cervical epiduritis, radiation plexopathy, hereditary sensible to pressure neuropathy, motor neuropathy with persistent multifocal conduction blocks, or, on the contrary, may confirm the normality of conduction, for example in anterior horn disease.

[Study of the proximal conduction of the arms using SEP and MEP]

The proximal conduction of the upper limb has been studied with the somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) in 40 controls which provided normal data. The SEP allowed the sensory conduction study of the Erb/C7 segment with N9/N13 delay determination after the median nerve stimulation at the wrist, and after the ulnar nerve stimulation at the wrist (20 cases) or above the elbow (20 cases). The N9/N13 delay was 3.24 ms +/- 0.35 for the median nerve, 3.30 ms +/- 0.52 for the ulnar nerve after stimulation at the wrist and 3.30 ms +/- 0.40 after stimulation at the elbow. The Erb point potential amplitude after ulnar nerve stimulation at the elbow was always greater than after the median nerve stimulation at the wrist: 13.2 microV versus 8.8 microV. The MEP allowed the C6/axilla motor conduction study. The recording was performed on the adductor digiti quinti. The proximal motor conduction velocity was 74 m/s +/- 8 (mini 60). The conduction delay was then 3.02 ms +/- 0.3. A constant amplitude loss was observed between the axilla and the cervical spine; it was never greater than 30% in controls. Allthings considered both methods provided very complementary data on the proximal nerve conduction of the upper limb at the brachial plexus. The conduction delay in the brachial plexus was around 3 ms and was very similar to the distal motor and sensory latencies of the median nerve at the wrist. Motor conduction blocks of more than 30% and 1 ms increament of the conduction delay were regarded as pathological.

Diagnostic value of electrical stimulation of lumbosacral roots in radiculopathies

Needle electrical stimulation of the lumbosacral roots at the laminar level of the Th12-L1 or L1-2 intervertebral spaces were performed in 24 normal subjects and 58 patients with various kinds of lumbar radiculopathy (unilateral L4, L5 and S1 herniated nucleus pulposus and lumber stenosis). The root stimulation method was compared with conventional needle EMG. Lumber electrical stimulation showed root abnormalities objectively in 80% of patients while the diagnostic value of needle EMG was 65%. Therefore, electrical root stimulation is superior to routine EMG for localizing lumbar root involvement. However, the only needle EMG demonstrated the root pathology in 7 cases (12%) and single electrophysiological abnormality was found by the root stimulation in 16 cases (27%). Thus, both electrophysiological methods should be complementary to each other in evaluation of the lumbar radioculopathy.

Comparison of magnetic coil stimulation and needle electrical stimulation in the diagnosis of lumbosacral radiculopathy

Electrical stimulation (ES) of lumbosacral nerve roots using a needle electrode inserted to the laminar level at the midline of Th12-L1 or L1-2 intervertebral interspace, was compared with magnetic stimulation using a 9-cm diameter coil (MCS) at the L3-4 or L4-5 spine levels, Compound muscle action potentials (CMAP) were superficially recorded from homologous muscles in both sides in 15 normal control subjects and in 20 patients with lumbosacral radiculopathy. Soleus muscles were used for S1, tibialis anterior (TA) for L5, and rectus femoris (RF) muscles for L4 roots. According to the clinical or radiological diagnosis (CAT, MRI and/or myelography) conventional needle EMG was capable to localise the root lesion in 16 of 20 patients (80%) and ES localised the root involvement in 18 of 20 patients (90%); the diagnostic value of MCS was lower, about 65% (13 of 20 patients). Although ES is uncomfortable and invasive, it is superior to needle EMG in localising unilateral or multiple lumbosacral root involvement. At present, MCS is not suitable for the diagnosis of lumbar radiculopathy.

Magnetic stimulation: C-8 root standardization based on arm length and arm position

Normal values for C-8 root distal latencies (DL) by magnetic stimulation (Magstim) have been reported; however, the methods of standardization have failed to consider the variables of arm length and arm position. Consequently, an artificial widening of the "normal" range occurs due to a false elevation of the standard deviation. In this study, Magstim of the C-8 nerve root was performed on 30 normal volunteers. Gender, hand temperature, age, arm length, and DL with the arm resting at the patient's side and fully abducted were recorded. DL was 13.3 +/- 1.1 ms with a side-to-side variation of 0.3 +/- 0.3 ms. The difference in DL between the arm at rest and in full abduction was 0.2 +/- 0.3 ms. Data analysis also demonstrated a direct correlation between arm length and DL. Utilizing this information a formula has been derived to more accurately describe the normal distribution of the C-8 root DL by Magstim.

Magnetic mapping of human cervical nerve roots: variation in normal subjects

Cervical magnetic stimulation occurs preferentially at the neural foramen and is more effective with the induced electric field oriented transversely to the spine rather than vertically. This geometry suggests the possibility of mapping innervation from specific nerve roots. A "butterfly" stimulus coil, positioned horizontally, was used to determine the morphologies and amplitudes of compound motor action potentials from multiple muscles in the upper extremities of 15 normal adults. Averages of 5 responses were taken at 1 cm intervals along the cervical-thoracic spine. Needle electrodes were used to verify atypical patterns of innervation. Cervical spine X-rays allowed anatomic correlation. Rarely abductor digiti minimi was difficult to stimulate in the horizontal orientation; satisfactory responses were then obtained with the stimulator angled upward towards the side of stimulation. Averaged compound motor action potentials were reproducible, and as the stimulus coil was moved rostro-caudally they often changed morphology in well-defined patterns, suggesting an origin in different cervical nerve roots. The sequence of muscle activation in most subjects was consistent with conventional descriptions of segmental innervation, but 5 appeared to show substantial variation in the nerve roots supplying one or more muscles. Magnetic mapping may be a useful method for studying segmental innervation in human subjects.

The optimal current direction for excitation of human cervical motor roots with a double coil magnetic stimulator

Upper limb muscles can easily be excited using magnetic stimulation with a circular coil over the cervical vertebrae. Double coil magnetic stimulators generate a more focal and directed form of stimulus and may offer an advantage in the more specific stimulation of individual motor roots. The aims of this study were to determine the optimal rostro-caudal locations and orientations of a double coil magnetic stimulator for excitation of the human 5th cervical to 1st thoracic motor roots. Compound muscle action potentials (CMAPs) evoked by magnetic stimuli were recorded from deltoid, brachioradialis, extensor digitorum communis and first dorsal interosseus muscles. Optimal rostro-caudal location was determined with the coil current flowing horizontally towards the midline. Optimal orientation was determined by rotating the coil in increments of 22.5 degrees about the optimal rostro-caudal location. In all subjects with all muscles examined, the best orientation was with the coil current flowing downwards towards the midline at a mean angle between 14.9 degrees and 27.6 degrees to the horizontal. Review of the anatomy of motor roots reveals a short upwardly directed segment within the intervertebral foramen and it is postulated that excitation occurs exclusively within this segment.

Sensory potentials evoked by magnetic stimulation of the cervical spine

Magnetic stimulation of cervical spinal roots was shown to elicit sensory potentials (MESP) which could easily be recorded at the fingers with ring electrodes. The latency of the MESP recorded at digit I was significantly shorter and the amplitude higher than of digits III and V. The latencies were largely independent of stimulus strength. In an attempt to localize the place of depolarization, the latencies of these potentials were compared with the N11 of the SEP (reflecting the arrival in the spinal cord) and with F-wave latencies and motor evoked potentials (MEP) to abductor pollicis brevis. The MESP latencies showed a very constant difference with the N11, being 0.6 ms faster. The mean difference between F latency and MEP was 1.2 ms. It is concluded that the origin of these MESPs is very near the spinal foramina, possibly in the sensory ganglia.

The value of magnetic stimulation in the diagnosis of radiculopathies

We studied 42 patients with cervical and lumbar radiculopathies using magnetic stimulation. Prolonged latencies following magnetic stimulation of the brain, the paravertebral spinal nerve, or both, showed a highly significant correlation with muscle weakness in clinical testing (24 of 26 patients with weakness had pathological motor evoked potentials) as well as with spontaneous activity of the target muscles in needle electromyography (24 of 25 subjects). The determination of both the central and the peripheral motor conduction time was found to be essential in patients with radiculopathies, because different patterns of latency changes correlated with different morphological results in computed tomography: in patients diagnosed as having a lateral compression of the nerve root the peripheral nerve latency was delayed; whereas, in patients with more medially localized herniations, a prolonged central motor latency was the most frequent finding. This study posits that combined magnetic stimulation of the brain and nerve root is an effective and painless technique for the noninvasive evaluation of nerve root function.

Lumbosacral nerve root stimulation comparing electrical with surface magnetic coil techniques

Stimulation of lumbosacral nerve roots using a monopolar needle electrode was compared with magnetic stimulation using a 7-cm diameter surface coil. Compound muscle action potentials were recorded from the tibialis anterior (TA) and flexor hallucis brevis (FHB) muscles. Although the mean latency of CMAPs did not differ using the two techniques, amplitudes were considerably larger using a needle. Mean amplitudes were 66% (TA) and 64% (FHB) of the direct M response obtained by distal, supramaximal stimulation compared with mean values using maximal magnetic coil stimulation of 36% (TA) and 25% (FHB). Minimum F-wave latencies from FHB were used to estimate the site of nerve root stimulation using both techniques. Although there was a large amount of variability in the data from individual subjects, the results suggested that, on the average, both forms of stimulation act proximal to the intervertebral foramen. We conclude that a needle electrode is a more suitable technique for stimulating lumbosacral nerve roots.

Examination of central and peripheral motor pathways by standardized magnetic stimulation

A standardized magnetic stimulation procedure for evaluation of central and peripheral motor pathways is described together with the results of motor evoked potential (MEP) recordings from 6 muscles in 50 healthy volunteers aged 18 to 60 years. Facilitation of the neuronal pathways was standardized using the integrated electric activity of the EMG as a gauge. The target muscles were: the brachial biceps (BB), the radial carpal flexor (FCR), the first dorsal interosseus of the hand (FDI), the medial vastus of the quadriceps muscle (VM), the anterior tibial (TA) and the abductor hallucis muscles (AH). The parameters used were the conduction times and the amplitudes of the CMAPs evoked by brain and root stimulation. CMAPs could be recorded from all muscles in all but three subjects in whom cortical stimulation was unsuccessful in one TA and two AHs, while root stimulation was negative in two TAs and one AH. Height and conduction times were significantly correlated, while age and conduction times were not. By linear regression 30-60% of the variation in the conduction times could be explained by the variation in height. The residual variation of the conduction times was less than in most other non-standardized studies and comparable to peripheral electrical motor conduction studies.

Sensorimotor central conduction time in comatose patients

Motor evoked potentials (MEPs) following magnetic stimulation were recorded in 22 patients comatose as a result of head injury (13 cases), stroke (7 cases) or anoxia (2 cases). Somatosensory evoked potentials (SEPs) from median nerve were recorded as well in 19 cases in the same session. Thirteen patients died or remained vegetative (59.1%), 3 were severely disabled (13.6%) and 6 showed a good recovery (27.3%). MEPs were significantly related to the outcome; they appeared to be a more accurate prognostic indicator than the Glasgow Coma Scale (GCS). However, 1 out of 6 patients with bilaterally absent MEPs (16.7%) showed a good recovery. SEPs were significantly related to the outcome as well, but the combined use of SEP and MEP improved the outcome prediction, decreasing the rate of false negatives. Two patients had normal sensorimotor function, 13 a combined sensorimotor dysfunction, while 4 had a pure motor dysfunction. Our results suggest that SEPs and MEPs may improve the assessment of sensorimotor dysfunction in comatose patients. A significant relationship between MEPs and outcome appears to exist, but the assessment of MEP reliability requires further study.