Characterizing the transcutaneous electrical recruitment of lower leg afferents in healthy adults: implications for non-invasive treatment of overactive bladder

Development of a Sham Protocol to Investigate Transcutaneous Tibial Nerve Stimulation in Randomised, Sham-Controlled, Double-Blind Clinical Trials

Transcutaneous tibial nerve stimulation (TTNS) is a promising treatment for neurogenic lower urinary tract symptoms. However, the evidence is limited due to a general lack of randomised controlled trials (RCTs) and, also, inconsistency in the sham and blinding conditions. In the context of much-needed RCTs, we aimed to develop a suitable sham-control protocol for a clinical setting to maintain blinding but avoid meaningful stimulation of the tibial nerve. Three potential electrode positions (lateral malleolus/5th metatarsal/plantar calcaneus) and two electrode sizes (diameter: 2.5 cm/3.2 cm) were tested to determine which combination provided the optimal sham configuration for a TTNS approach, based on a visible motor response. Sixteen healthy volunteers underwent sensory and motor assessments for each sham configuration. Eight out of them came back for an extra TTNS visit. Sensory thresholds were present for all sham configurations, with linear regression models revealing a significant effect regarding electrode position (highest at plantar calcaneus) but not size. In addition, motor thresholds varied with the position-lowest for the 5th metatarsal. Only using this position and 3.2 cm electrodes attained a 100% response rate. Compared to TTNS, sensory and motor thresholds were generally higher for the sham configurations; meanwhile, perceived pain was only higher at the lateral malleolus. In conclusion, using the 5th metatarsal position and 3.2 cm electrodes proved to be the most suitable sham configuration. Implemented as a four-electrode setup with standardized procedures, this appears to be a suitable RCT protocol for maintaining blinding and controlling for nonspecific TTNS effects in a clinical setting.

Prolonged inhibition of bladder function is evoked by low-amplitude electrical stimulation of the saphenous nerve in urethane-anesthetized rats

To better understand the effects of saphenous nerve (SN) stimulation on bladder function, we investigated the duration of electrical stimulation as a key variable in eliciting urodynamic changes. SN stimulation is a novel approach to electrically modulating bladder function. In previous animal studies, bladder-inhibitory responses were evoked by low-amplitude (25 μA) stimulus pulses applied in short-duration (10 min) trials and at frequencies between 10 and 20 Hz. Experiments were performed in urethane-anesthetized rats that were separated into three groups: intravesical saline infusion + SN stimulation (group A), intravesical 0.1% acetic acid infusion + SN stimulation (group B), and intravesical saline infusion + no SN stimulation (group C). Changes in bladder function- basal bladder pressure (P base ), contraction amplitude (ΔP), and inter-contraction interval (T ICI )-were measured in response to stimulation trials applied for different durations (10, 20, and 40 min). Trials were also repeated at frequencies of 10 and 20 Hz. In group A, longer-duration (40 min) stimulation trials applied at 10 Hz evoked overflow incontinence (OI) episodes that were characterized by significant changes in P base (122.7 ± 9.1%, p = 0.026), ΔP (-60.8 ± 12.8%, p = 0.044), and T ICI (-43.2 ± 13.0%, p = 0.031). Stimulation-evoked OI was observed in 5 of 8 animals and lasted for 56.5 ± 10.7 min. In contrast, no significant changes in bladder function were observed in either group B or group C. Our findings show that longer-duration trials consisting of electrical pulses applied at 10 Hz are important stimulation parameters that elicit inhibitory bladder responses in anesthetized rodents.

Randomised Crossover-Controlled Evaluation of Simultaneous-Bilateral Transcutaneous Electrostimulation of the Posterior Tibial Nerve During Urodynamic Studies on Patients With Lower Urinary Tract Symptoms

Purpose

Transcutaneous tibial nerve stimulation (TTNS) has proven to be a valuable treatment option for various lower urinary tract conditions, such as overactive bladder syndrome and neurogenic detrusor overactivity. The aim of this study was to investigate acute changes in urodynamic parameters due to bilateral TTNS.

Methods

Fifty-one patients (18–87 years; 61% female) with various lower urinary tract symptoms were enrolled in this study. They were single-blinded and randomly assigned to receive simultaneous bilateral TTNS either during their first urodynamic examination, followed by a second round using a placebo stimulation technique, or vice versa.

Results

For subjects without signs of anatomical pathologies, the filling volume at the first desire to void (FDV) increased significantly by 54 mL (interquartile range [IQR], 26–81 mL; P<0.01) under the influence of TTNS compared to placebo. The maximum cystometric capacity increased by 41 mL (IQR, 10–65 mL; P=0.02). The median micturition volume of patients with pathological postvoid residual volumes (>100 mL) increased by 76 mL compared to patients without urinary retention (IQR, 6–166 mL; P=0.03).

Conclusions

Compared to placebo, simultaneous bilateral TTNS showed significant improvements in bladder functioning, such as delayed FDV, increased maximum cystometric capacity, and reduced urinary retention. Patients with signs of anatomical pathologies did not seem to benefit from TTNS. Further studies need to be conducted to compare the effectiveness of bilateral versus unilateral TTNS.

[Treatment for refractory non-neurogenic overactive bladder]

INTRODUCTION

The aim was to synthesize current knowledge on refractory overactive bladder treatments.

METHOD

A systematic literature review based on PubMed, Embase and Google Scholar was conducted in July 2020.

RESULTS

Today, refractory overactive bladder treatment includes tibial nerve stimulation, whether percutaneously or transcutaneously, sacral neuromodulation, and botulinum toxin A detrusor injections. These conservative treatments have marginalized surgical treatments, which mainly involve supratrigonal cystectomy with augmentation cystoplasty. Several potential new treatments are being evaluated but can only be currently offered as part of clinical research protocols.

CONCLUSION

"Conservative" treatments for refractory overactive bladder have been shown to be effective. Other treatments could enrich the treatment options.

Enhanced transcutaneous electrical nerve stimulation achieved by a localized virtual bipole: a computational study of human tibial nerve stimulation

OBJECTIVE

Electrical neuromodulation is a clinically effective therapeutic instrument, currently expanding into newer indications and larger patient populations. Neuromodulation technologies are also moving towards less invasive approaches to nerve stimulation. In this study, we investigated an enhanced transcutaneous electrical nerve stimulation (eTENS) system that electrically couples a conductive nerve cuff with a conventional TENS electrode. The objectives were to better understand how eTENS achieves lower nerve activation thresholds, and to test the feasibility of applying eTENS in a human model of peripheral nerve stimulation.

APPROACH

A finite element model (FEM) of the human lower leg was constructed to simulate electrical stimulation of the tibial nerve, comparing TENS and eTENS. Key variables included surface electrode diameter, nerve cuff properties (conductivity, length, thickness), and cuff location. Enhanced neural excitability was predicted by relative excitability (RE > 1), derived using either the activating function (AF) or the nerve activation threshold (MRG model).

MAIN RESULTS

Simulations revealed that a localized 'virtual bipole' was created on the target nerve, where the isopotential surface of the cuff resulted in large potential differences with the surrounding tissue. The cathodic part (nerve depolarization) of the bipole enhanced neural excitability, predicted by RE values of up to 2.2 (MRG) and 5.5 (AF) when compared to TENS. The MRG model confirmed that action potentials were initiated at the cathodic edge of the nerve cuff. Factors contributing to eTENS were larger surface electrodes, longer cuffs, cuff conductivity (>1×10³ S m^-1), and cuff position relative to the cathodic surface electrode.

SIGNIFICANCE

This study provides a theoretical basis for designing and testing eTENS applied to various neural targets and data suggesting function of eTENS in large models of nerve stimulation. Although eTENS carries key advantages over existing technologies, further work is needed to translate this approach into effective clinical applications.

Electrical stimulation in the treatment of bladder dysfunction: technology update

The urinary bladder has two functions: urine storage and voiding. Clinically, two major categories of lower urinary tract symptoms can be defined: storage symptoms such as incontinence and urgency, and voiding symptoms such as feeling of incomplete bladder emptying and slow urinary stream. Urgency to void with or without incontinence is called overactive bladder (OAB). Slow urinary stream, hesitancy, and straining to void with the feeling of incomplete bladder emptying are often called underactive bladder (UAB). The underlying causes of OAB or UAB can be either non-neurogenic (also referred to as idiopathic) and neurogenic, for example due to spinal cord injury or multiple sclerosis. OAB and UAB can be treated conservatively by lifestyle intervention or medication. In the case that conservative treatment does not provide sufficient benefit, electrical stimulation can be used. Sacral neurostimulation or neuromodulation (SNM) is offered as a third-line therapy to patients with non-neurogenic OAB or UAB. In SNM, the third or fourth sacral nerve root is stimulated and after a test period, a neuromodulator is implanted in the buttock. Until recently only a non-rechargeable neuromodulator was approved for clinical use. However, nowadays, a rechargeable sacral neuromodulator is also on the market, with similar safety and effectiveness to the non-rechargeable SNM system. The rechargeable device was approved for full body 1.5T and 3T MRI in Europe in February 2019. Regarding neurogenic lower urinary tract dysfunction, electrical stimulation only seems to benefit a selected group of patients.