Overactive bladder syndrome negatively affects the daily life of many people. First-line conservative treatments, such as antimuscarinics, do not always lead to sufficient improvement of the complaints and/or are often associated with disabling adverse effects leading to treatment failure. Electrical stimulation of the sacral nerves has emerged as an alternative and attractive treatment for refractory cases of bladder overactivity. Few theories attempted to explain its mechanism of action which remains elusive. It involves percutaneous posterior tibial nerve stimulation and more commonly sacral neuromodulation. For the latter, temporary sacral nerve stimulation is the first step. If the test stimulation is successful, a permanent device is implanted. The procedure is safe and reversible. It carries a durable success rate. The technique should be combined with careful followup and attentive adjustments of the stimulation parameters in order to optimize the clinical outcomes. This paper provides a review on the indications, possible mechanisms of action, surgical aspects and possible complications, and safety issues of this technique. The efficacy of the technique is also addressed.
Overactive bladder (OAB) also referred to as the urgency-frequency syndrome, with or without urge urinary incontinence, can considerably impair the patient’s quality of life. It is widely accepted that diet and life style modifications, behavioural therapy, and medication belong to the standard conservative therapeutic options and are considered as first-line measures. The International Consultation on Incontinence (ICI) guidelines states that when the first-line approach is not fully satisfactory or fails after 8–12 weeks, alternative therapies should be sought out [
In the settings of OAB, electrical neuromodulation devices act to modulate detrusor contractions. The use of neuromodulation is based on the knowledge that urge incontinence usually results from an imbalance of inhibitory and excitatory control systems, often causing a “hyperactive” detrusor, leading to incontinence during the filling phase [
This concept has become popular since it bridges the gap between conservative treatment and highly invasive options. Currently, these devices include SNM via surgically implanted electrodes and newer methods that deliver percutaneous stimulation of the peripheral tibial nerve. The exact mechanism of action is not well understood. A number of theories have been proposed to explain the effect of electrical neuromodulation which can be summarized as follows. In human subjects, it was shown that sensory input through the pudendal nerve inhibited detrusor activity and, therefore, pudendal nerve stimulation and enhancement of external sphincter tone may serve to control bladder overactivity and facilitate urine storage [ The bladder tends to respond to neural stimulation initially with rapid contraction followed by slow, longer-lasting relaxation. With recurrent, repetitive stimuli produced by the electrical stimulation, there is a decay and downregulation of the bladder’s response, thus reducing the detrusor muscle overactivity [ Stimulation of afferent sacral nerves in either the pelvis or lower extremities increases the inhibitory stimuli to the efferent pelvic nerve and reduces detrusor contractility. One theory is that there is supraspinal inhibition of the detrusor [ It is assumed that neuromodulation affects the “neuroaxis” at various levels and restores the balance between excitatory and inhibitory regulation at various locations within the peripheral and central nervous system [
PTNS is a minimally invasive, office-based procedure that involves percutaneous placement of a 34-gauge (ga) needle over the medial malleolus of the ankle with subchronic electrical stimulation of the posterior tibial nerve. The procedure is a 30-minute treatment session administered over a period of 12 weeks. Another method that has been described is implanting the device in the same area as well [
PTNS has shown some promise in the treatment of patients with refractory urge incontinence. McGuire et al. originally reported the first study applying PTNS in 1983 [
SNM uses mild electrical pulses to activate or inhibit neural reflexes by continuously stimulating the sacral nerves that innervate the pelvic floor and lower urinary tract; it is also referred to as the pacemaker for the bladder. The technique was pioneered by Schmidt et al. at the University of California in San Francisco who introduced it in 1979 [
Preprocedure patient counselling is critical in reassuring the patient and managing treatment expectations. Once it has been decided that the patient is an appropriate candidate for InterStim therapy, implantation proceeds in 2 steps: a test phase and implantation or lead removal based on test response. The initial test phase can be performed in the office or operating room allowing for placement of the lead with a test period of 1 to 2 weeks; full implantation can be performed under local or general anesthesia. Patients are counselled that approximately 60% of patients undergoing office-based test stimulation and 70% undergoing operating room-based test stimulation will have a positive test response [
In the 1990s, Schmidt et al. devised a simple outpatient diagnostic test that involved percutaneous placement of a wire to stimulate the S3 nerve root and evaluate motor and sensory responses [
Limitations of this approach include migration of the temporary wires and a suboptimal test phase, as well as the potential discrepancy in clinical response when the permanent quadripolar lead is implanted. Short-term testing period as well as the lead migration probably explain the relatively low success rate of PNE, estimated at around 50% [
If the patient is not a candidate for office-based test stimulation or did not respond to the in-office test, test stimulation may be performed in the operating room (OR). Furthermore, the shift from PNE (one-stage implant) to a two-stage procedure helps to minimize technical-related failures and increase test efficacy and patient selection. Immediate implantation of a permanent lead aims to avoid lead migration and allows prolonged patient testing/screening [
This procedure is similar to the office-based test but involves tined quadripolar leads, thus improving lead fixation and test response, and can be performed using intravenous (IV) sedation, local anaesthesia, or general anaesthesia. In case general anaesthesia is used, the anaesthetist is reminded to avoid using any long-acting muscle relaxants that may impair the ability to stimulate the sacral nerves or visualize their motor response. Fluoroscopy with C-arm should be utilized to facilitate placement. Once the right or left S3 foramen has been identified and subsequently chosen, the permanent tined lead is passed through the foramen needle. The lead is then exposed and tested in the 0, 1, 2, and 3 positions for response. Then, the sheath is carefully removed so as not to move the lead and expansion of the tines fix the lead in place. The lead is then tunnelled deeply through the subcutaneous fat to a position in the right or left buttock depending on the patient’s dominant hand side where the permanent implantable pulse generator (IPG) will be placed eventually during the second stage. The lead is attached to the temporary connector and then tunneled through the subcutaneous fat to an alternative exit site. This is particularly an important step because if the patient were to get a superficial skin infection, then alternative exit site would help prevent the infection from spreading to the location of the permanent IPG and back to the lead [
A prospective, randomized study showed that the two-stage implant technique of SNM has a higher success rate compared to the one-stage method, despite prior positive PNE, both in the short term and in the long term [
After a successful test phase, the patient is brought to the OR for implantation of the implantable generator (IPG). If the first test stimulation was office based, fluoroscopy is required to place the permanent lead. The quadripolar tined lead is inserted in a similar fashion on the side where the patient had the best in-office test response. The lead is then tunnelled deeply through the subcutaneous fat to an incision in the right or left buttock region. It is attached to the IPG and buried in the deep subcutaneous pocket. On the other hand, if the first phase was done in the OR and there is pre-existing placement of the permanent quadripolar lead, the implant stage is quick, does not require fluoroscopy, and can be performed under local or general anaesthesia. The previous incision where the temporary connector was placed in the buttock is opened, and the permanent IPG is then connected to the lead and buried in a deep subcutaneous pocket in the buttock. Buttock placement of the IPG has become an attractive alternative to subcutaneous implant in the lower part of the anterior abdominal wall because of the lower incidence of adverse events (approximately 2-fold), shorter operation time, and avoidance of patient repositioning during the operation [
The very nature of this mode of therapy mandates a 100% reoperation to replace the IPG at some point due to the limited longevity of the neurostimulator. Adverse events are usually related to the implant procedure and the presence of the implant or of undesirable stimulation. The most common adverse events include lead migration, implant site pain, bowel dysfunction, and infection. The majority of adverse events do not require surgical intervention. Potential lead migration can be simply resolved without significant morbidity in the majority of patients by reprogramming, reinforcing the lead, or inserting a new lead contralaterally [
Contraindications for the patient with an implanted device include shortwave diathermy, microwave diathermy, or therapeutic ultrasound diathermy. The diathermy’s energy can be transferred through the implant and could be harmful. MRI is not recommended. Nevertheless, Elkelini and Hassouna reported on six patients with implanted sacral nerve stimulator who underwent eight MRI examinations at 1.5 Tesla conducted in areas outside the pelvis [
Several investigators have attempted to identify parameters that have predictive value in selecting the best candidates and those patients most likely to benefit from SNM therapy. Amundsen at al. reported that age >55 years and more than three chronic conditions were independent factors associated with a lower cure rate in patients implanted with a sacral neuromodulator for refractory urge incontinence [
There is convincing evidence for the success of SNM with the Interstim technique for refractory OAB. Several studies including RCTs and long-term observational studies reported fair clinical response between 64 and 88% of all patients [
Recently, several technical aspects of SNM with InterStim therapy led to the development of the InterStim II system, which received regulatory approval in Europe and the United States in 2006. InterStim II eliminates the need for extension cables and is almost 50% lighter and smaller in volume compared to the initial model. Subsequently, this allows for a smaller incision and smaller pocket to be created and thus less patient discomfort with higher patient acceptance which is of particular importance for skinny patients. However, the above-mentioned advantages come with the expense of a shorter battery life. Most new implanted IPGs are supplied with small iCon patient programmers, offering the patients the possibility to choose from up to four preset programs, provided better control of stimulation by the patient. Other available SNM technology includes the twin-chamber IPGs that can feed two electrodes providing synergetic effect.
Electrical neuromodulation devices act to modulate detrusor contractions. Currently, these devices include SNM and PTNS. SNM is an effective treatment modality for patients with refractory OAB and should be offered before applying more invasive, irreversible treatments. The procedure is safe and minimally invasive involving one or two-stage implantation. It carries small, treatable, and nonpermanent side effects. Although the mechanisms behind its action are still not fully understood, the therapy has been shown to be effective in the long term. Followup should include regular checks to determine efficacy of the therapy and a review of the electrical system. The SNM technology continues to evolve.