Motor evoked potentials from the pelvic floor

What Does Electromyography Tell Us About Dyspareunia?

INTRODUCTION

Emergent evidence suggests that pelvic floor muscle (PFM) dysfunction contributes to dyspareunia, the experience of pain on vaginal penetration. Electromyography (EMG) is a valuable tool for the assessment of neuromuscular control and could be very useful in enhancing our understanding of PFM involvement in sexual function and in conditions such as dyspareunia. However, PFM EMG must be interpreted within the context of the many factors that can influence findings.

AIM

To outline the main factors to consider when evaluating PFM EMG for female sexual function and dyspareunia and to synthesize the literature in which EMG has been acquired and interpreted appropriately in this context.

METHODS

Standards for the acquisition and interpretation of EMG were retrieved and consulted. An exhaustive search of four electronic databases (Embase, CINAHL, PubMed, and PsycLit) and hand searching references from relevant articles were performed to locate articles relevant to PFM involvement in sexual function and in dyspareunia in which EMG was used as a primary outcome. Study outcomes were evaluated within the context of the appropriate application and interpretation of EMG and their contribution to knowledge.

MAIN OUTCOME MEASURES

A synthesis of the evidence was used to present the current state of knowledge on PFM involvement in sexual function and in dyspareunia.

RESULTS

Few standards documents and no practice guidelines for the acquisition and interpretation of PFM EMG are available. Some cohort studies with small samples of women have described the role of the PFMs in female sexual function. The literature on PFM involvement in dyspareunia also is limited, with outcomes suggesting that higher than normal tonic activation and higher than normal reflex responses might be present in the superficial PFM layer and might be characteristic features of dyspareunia. The data are less clear on the involvement of the deep layer of the PFMs in dyspareunia.

CONCLUSION

Guidelines for the application and interpretation of PFM EMG in the context of sexual function and dyspareunia are needed. When interpreted within the context of their strengths and limitations, EMG data have contributed valuable information to our understanding of PFM involvement in dyspareunia. The literature to date suggests that the superficial PFMs might have higher than normal tone and exaggerated responses to tactile or penetrative provocation in at least some women with dyspareunia. McLean L, Brooks K. What Does Electromyography Tell Us About Dyspareunia? Sex Med Rev 2017;5:282-294.

A practical guide to diagnostic transcranial magnetic stimulation: report of an IFCN committee

Transcranial magnetic stimulation (TMS) is an established neurophysiological tool to examine the integrity of the fast-conducting corticomotor pathways in a wide range of diseases associated with motor dysfunction. This includes but is not limited to patients with multiple sclerosis, amyotrophic lateral sclerosis, stroke, movement disorders, disorders affecting the spinal cord, facial and other cranial nerves. These guidelines cover practical aspects of TMS in a clinical setting. We first discuss the technical and physiological aspects of TMS that are relevant for the diagnostic use of TMS. We then lay out the general principles that apply to a standardized clinical examination of the fast-conducting corticomotor pathways with single-pulse TMS. This is followed by a detailed description of how to examine corticomotor conduction to the hand, leg, trunk and facial muscles in patients. Additional sections cover safety issues, the triple stimulation technique, and neuropediatric aspects of TMS.

Application of magnetic motor stimulation for measuring conduction time across the lower part of the brachial plexus

OBJECTIVE

The objective of this study was to calculate central motor conduction time (CMCT) of median and ulnar nerves in normal volunteers. Conduction time across the lower part of the brachial plexus was measured by using magnetic stimulation over the motor cortex and brachial plexus and recording the evoked response in hand muscles.

DESIGN

This descriptive study was done on 112 upper limbs of healthy volunteers. Forty-six limbs belonging to men and sixty-six belonging to women were studied by magnetic stimulation of both motor cortex and brachial plexus and recording the evoked response in thenar and hypothenar muscles. Stimulation of the motor cortex gives rise to absolute latency of each nerve whereas stimulation of the brachial plexus results in peripheral conduction time. The difference between these two values was considered the central motor conduction time (CMCT).

RESULTS

In summary the result are as follows; Cortex-thenar latency = 21.4 ms (SD = 1.7), CMCT-thenar = 9.6 ms (SD = 1.9), Cortex-hypothenar latency = 21.3 ms (SD = 1.8), CMCT-hypothenar = 9.4 ms (SD = 1.8).

CONCLUSION

These findings showed that there is no meaningful difference between two genders. CMCT calculated by this method is a little longer than that obtained by electrical stimulation that is due to the more distally placed second stimulation. We recommend magnetic stimulation as the method of choice to calculate CMCT and its use for lower brachial plexus conduction time. This method could serve as a diagnostic tool for diagnosis of lower plexus entrapment and injuries especially in early stages.

Neurophysiology of the neurogenic lower urinary tract disorders

The nervous system structures involved in the control of the lower urinary tract (LUT) are usually divided using a neuroanatomical classification system into suprapontine, pontine, spinal and sacral. In all patients with LUT symptoms, after exclusion of local causes, a nervous system disorder needs to be considered. For the diagnosis of neurogenic LUT disorders, in addition to clinical assessment, neurophysiologic testing might be useful. Imaging and other laboratory studies (e.g., cystometry) often provide relevant additional information. Neurophysiologic tests are more useful in patients with sacral compared with suprasacral disorders. Although in patients with LUT disorders external urethral sphincter (EUS) electromyography (EMG) would seem the most appropriate, anal sphincter EMG is the single most useful diagnostic test, particularly for focal sacral lesions, and atypical parkinsonism. Another clinically useful method that tests the sacral segments, and complements EMG, is the sacral (penilo/clitoro-cavernosus) reflex. Kinesiologic EMG is useful to demonstrate detrusor sphincter dyssynergia (i.e., increased EUS activity during bladder contraction), which is particularly common in spinal cord disease. Somatosensory evoked potential (SEP) and motor evoked potential (MEP) studies (cortical and lumbar) may be useful to diagnose clinically silent central lesions. MEP, in addition, seems to be very promising in research into cortical excitability. Theoretically, cortical SEP on bladder/urethra stimulation would be much more useful than pudendal SEP because it tests thin nerve afferents from the pelvic viscera. However, the utility of this technique is limited by technical difficulties, which can be partially overcome by the concomitant recording of a palmar sympathetic skin response (SSR). SSR recorded from the saddle region is also useful for testing the lumbosacral sympathetic system. Although the technique of detrusor EMG has been recently described in humans, a clinically useful test for evaluating the sacral parasympathetic system, which is crucial for LUT functioning, is still lacking.

Assessing the temporal reproducibility of human esophageal motor-evoked potentials to transcranial magnetic stimulation

BACKGROUND

Although the electrophysiological properties and reproducibility of somatic limb motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) are well characterized, little is known about the reproducibility of MEPs for viscerosomatic structures such as the esophagus.

AIM

To determine the temporal reproducibility of esophageal MEPs to TMS.

METHODS

MEPs to TMS were recorded from the proximal esophagus, using a swallowed catheter housing a pair of electrodes, in eight healthy subjects at five stimulus intensities (SI) (motor threshold [MT] to 20% above MT). For each SI, 20 consecutive TMS stimuli at 5-second intervals were delivered over a single scalp site (dominant hemisphere at site exhibiting MT at lowest SI) and repeated 40 and 80 minutes thereafter. MEP amplitudes and latencies were measured, and means were sequentially calculated for each SI and then log-transformed. The repeatability coefficients (RC) for the three time points were calculated across each set of 20 stimuli and presented as an exponential ratio.

RESULTS

Best RC (amplitude/latency) were achieved at 120% SI relative to MT, being 1.8/1.2 (optimal = 1.0). For lower intensities of 115%, 110%, 105%, and 100% SI, the RC were 2.1/1.2, 2.1/1.1, 2.4/1.2, and 2.6/1.4, respectively. For all SI, the greatest reductions in RC occurred over the first 10 stimuli, with little additional gain beyond this number.

CONCLUSIONS

Latencies of esophageal MEP to TMS across intensities are highly reproducible, whereas amplitudes are more stimulus intensity-dependent, being most reliable and reproducible at the highest stimulus strengths.

SIGNIFICANCE

Using careful parameters, TMS can be used reliably in future studies of viscerosomatic structures, although the size of the response variability needs to be taken into account when assessing changes in cortico-fugal activity.

Acute urinary retention due to benign inflammatory nervous diseases

Both neurologists and urologists might encounter patients with acute urinary retention due to benign inflammatory nervous diseases. Based on the mechanism of urinary retention, these disorders can be divided into two subgroups: disorders of the peripheral nervous system (e.g., sacral herpes) or the central nervous system (e.g., meningitis-retention syndrome [MRS]). Laboratory abnormalities include increased herpes virus titers in sacral herpes, and increased myelin basic protein in the cerebrospinal fluid (CSF) in some cases with MRS. Urodynamic abnormality in both conditions is detrusor areflexia; the putative mechanism of it is direct involvement of the pelvic nerves in sacral herpes; and acute spinal shock in MRS. There are few cases with CSF abnormality alone. Although these cases have a benign course, management of the acute urinary retention is necessary to avoid bladder injury due to overdistension. Clinical features of sacral herpes or MRS differ markedly from those of the original "Elsberg syndrome" cases.

Understanding detrusor sphincter dyssynergia—significance of chronology

OBJECTIVES

To evaluate in patients with spinal cord injury (SCI) and detrusor sphincter dyssynergia (DSD) whether the onset of external urethral sphincter (EUS) contractions precedes or follows the onset of bladder contractions and to address the issue of potential therapeutic approaches based on the understanding of DSD chronology.

METHODS

A retrospective review of video-urodynamic recordings of patients with SCI that demonstrated both untreated neurogenic overactive bladder and DSD, from January 2002 to December 2003, was performed. Delay A was defined as the period between the onset of an EUS pressure increase and the onset of a bladder pressure increase and delay B as the period between the onset of a urethral sphincter pressure increase and the moment at which the bladder pressure increase reached 10 cm H2O greater than the baseline value.

RESULTS

Twenty patients with traumatic SCI matched all inclusion criteria. Delay A was positive (EUS contracted first) in 16 (80%) of 20 patients. The mean time for delay A was 2.2 seconds. A positive association was found among a positive delay A, the completeness of the spinal lesion, and continuous DSD type. Delay B was positive in all 20 patients (100%). The mean time for delay B was 7.6 seconds.

CONCLUSIONS

In most patients with SCI and DSD, the EUS contraction started before the onset of the bladder contraction. Additionally, in all patients with SCI, the EUS contraction started before the critical part of the bladder contraction. A pathophysiologic hypothesis for such chronology is discussed. A potential therapeutic application would be to use urethral sphincter activity to trigger inhibition of bladder contractions (conditional neuromodulation) and treat the neurogenic overactive bladder.

Conditioning stimulus can influence an external urethral sphincter contraction evoked by a magnetic stimulation

AIMS

To study the effect of a conditioning stimulus on an external urethral sphincter (EUS)contraction evoked by a magnetic stimulation at different time intervals.

METHODS

Seven healthy male volunteers underwent EUS pressure measurement. At baseline, magnetic stimulation of the lumbosacral spinal cord above the motor threshold was performed and evoked EUS pressure responses were recorded. The lumbosacral magnetic stimulation was repeated with same intensity, while a selective electrical dorsal penile nerve stimulation below the bulbocavernosus reflex (BCR) threshold was preceding at five different intervals (10, 20, 30, 50, 100 msec). The protocol was performed with empty and full bladder (BLA), and baseline responses were statistically compared to those with combined stimulation.

RESULTS

When the dorsal penile nerve electrical stimulation preceded the lumbosacral magnetic stimulation by 20 msec (P=0.0048), 50 msec (P=0.0039), or 100 msec (P=0.0002), the amplitudes of the EUS pressure response with empty BLA were significantly reduced compared to lumbosacral magnetic stimulation alone. With a filled BLA, the amplitudes of the EUS were significantly reduced only at an interval of 50 msec (P<0.0001).

CONCLUSIONS

A conditional sensory pudendal stimulation seems to have the capacity to inhibit the external urethral sphincter contraction induced by a magnetic stimulation. The inhibitory effect seems to depend on the latency between the peripheral and lumbosacral stimulation as well as on the degree of BLA filling. It remains to be proved if the neuromodulative effect of the conditional stimulus occurs at a spinal or supraspinal level.