Written by Mr Jai Seth, BSc(Hons) MBBS MRCS MSc(Urol) MD(Res) FRCS(Urol)
Consultant Urological Surgeon · Last updated:
In short
- Treats
- Severe overactive bladder, or retention, after other options have failed
- What happens
- A fine lead near a sacral nerve, connected to a small implanted stimulator
- Two stages
- A two-to-four-week test with a lead run to an external stimulator before any implant
- Anaesthetic
- Local for the test; local or general for the implant
- Who responds
- Around 70 to 80% pass the test phase
- Battery
- Three to 15 years, depending on the device and settings; some are rechargeable
- Worth knowing
- Nothing permanent is placed unless the test stage works for you; MRI limits depend on the device
- NHS or private
- Both; recommended by NICE
- Right for you?
- Depends on your response in the test stage, which is measured against your own bladder diary
SNM is recommended by NICE (HealthTech guidance 37, formerly IPG64, for urge incontinence and urgency-frequency; HealthTech guidance 391, formerly IPG536, for non-obstructive retention) and is one of the third-line options in NICE NG123 for refractory OAB, alongside bladder Botox and PTNS. The defining feature of the treatment is its two-stage design: every patient has a test phase first, with a lead connected to a stimulator worn outside the body, to confirm whether the treatment will work for them before any permanent implant is offered. The implant procedure itself is undertaken in a hospital theatre under local or general anaesthetic.
Who is it suitable for?
- Refractory overactive bladder with urgency, frequency and urge incontinence that has not responded to lifestyle, medication, and at least one other third-line option (bladder Botox or PTNS)
- Chronic non-obstructive urinary retention requiring intermittent self-catheterisation
- Faecal incontinence (a separate but overlapping indication; SNM is sometimes considered when bladder and bowel symptoms co-exist)
- Patients able to attend follow-up and use the patient programmer to manage settings at home
- No active urinary or skin infection at the implant site
- MRI compatibility is reviewed at consultation, modern systems are MRI-conditional, but specifics depend on the device
- Pregnancy and certain neurological conditions are reviewed individually
How does it work?
- A fine lead is placed close to the third sacral nerve through a small entry point in the lower back, under image guidance (X-ray fluoroscopy)
- Continuous low-frequency electrical pulses delivered through the lead modulate the nerve signals travelling between the bladder and the brain
- The stimulation calms the over-active feedback loop driving urgency and urge incontinence in OAB; in patients with non-obstructive retention, it can re-establish more coordinated bladder emptying
- Patients adjust amplitude and stimulation patterns at home using a small remote programmer, within ranges set by the clinician
- Modern devices are rechargeable or non-rechargeable; battery life ranges from around three to 15 years depending on the device and settings (BAUS patient leaflet, 2025), and rechargeable systems need charging weekly or fortnightly
What to expect
Before the procedure
- A formal assessment confirms that lifestyle, medication and at least one other third-line option have been tried
- A urine sample, post-void residual scan and recent bladder diary are reviewed
- Medications that increase bleeding risk (aspirin, clopidogrel, anticoagulants) are reviewed and adjusted around the test-phase and implant procedures as needed
- MRI history and any planned future imaging are discussed, the chosen device is matched to the patient's likely needs
On the day
- Stage 1 (test phase) is performed under local anaesthetic, sometimes with light sedation. A lead, temporary or the permanent type depending on the approach chosen, is placed under X-ray guidance and connected to an external stimulator worn on a belt
- The test phase usually runs for two to four weeks (BAUS). During this time, the patient keeps a bladder diary so the response can be quantified against the baseline
- If response at the end of the test phase is good (typically defined as ≥ 50% reduction in symptom frequency or leakage episodes), Stage 2, permanent implantation of the lead and pulse generator, is offered, usually a few weeks later
- Stage 2 is performed under local or general anaesthetic. The permanent lead is placed and connected to a small pulse generator implanted under the skin in the upper buttock, comparable in size to a cardiac pacemaker generator
- If response in the test phase is not adequate, the lead is simply removed and no permanent implant is placed. The patient avoids permanent surgery on a treatment that would not have worked
Recovery and aftercare
- After Stage 1, patients keep the external stimulator on, manage it with a programmer, and continue normal activities while keeping the dressings clean and dry, which means no showering or bathing during the test phase (BAUS)
- After Stage 2, patients avoid strenuous activity, sport and stretching the lower back for six to 12 weeks, because these can move the lead out of position (BAUS); contact sports, extreme sports and horse riding are advised against long term
- Stimulation settings are reviewed and fine-tuned in the weeks after implantation. Most patients have their settings within their preferred range by three months
- Long-term follow-up is typically every 6–12 months once settings are stable, plus device interrogation as needed
Outcomes and evidence
- Test-phase success rates (≥50% symptom reduction) of around 70–80% are reported across published series for refractory OAB with urge incontinence
- In long-term follow-up of patients who proceeded to permanent implant, the InSite trial (Siegel et al., 2018, J Urol) reported 82% therapeutic success at 5 years for urge incontinence
- Sustained response over 5–10 years is well documented in registry and trial data; battery replacement is the most common long-term intervention
- SNM works for some patients in whom Botox and PTNS have not worked, and vice versa, the mechanisms are different and not interchangeable
Risks and complications
- Needing the stimulator or lead replaced, moved or removed at some point, in around 1 in 4 patients (BAUS); lead movement is the usual reason, and strenuous activity or stretching the lower back in the first six to 12 weeks makes it more likely
- Discomfort at the stimulator or lead site in around 1 in 7, discomfort in the ankle or foot in around 1 in 10, and wound infection needing antibiotics and possibly removal of the device in around 1 in 25 (BAUS); redness, discharge or throbbing at the wound is reported to the hospital straight away
- No significant improvement in about 3 in 10 patients, and a gradual loss of effect over time as the body adjusts, usually overcome by reprogramming and occasionally needing lead revision (BAUS)
- An unwanted effect on bowel function from the stimulation, in between 1 in 10 and 1 in 50 (BAUS)
- The device can be damaged by surgical diathermy during any later operation and by MRI other than head scans, and it can set off shop and airport security scanners; it comes with an identification card and is switched off for surgery and screening (BAUS)
- Battery depletion at the end of useful life, replacement is a smaller second procedure rather than a full re-implant
- MRI restrictions depending on the device; modern systems are increasingly MRI-conditional but the specific limits matter and are confirmed before any imaging
- Two-stage design means a small surgical procedure for the test phase even before the permanent implant, this is the trade-off for the safety of confirming response first
- Set against these, around 70 to 80% of patients pass the test phase, and of those who go on to the implant, 82% were still helped at five years in the InSite trial. The implant can be switched off or removed if you no longer want it.
- Your own risk is shaped by what is checked beforehand: medicines that increase bleeding (adjusted around both procedures), any likely need for MRI (the device is matched to it), skin or urinary infection at the time of surgery, and how you get on with the programmer during the test phase. Because nothing permanent is placed until the test has worked, the biggest risk of all, an implant that does not help, is the one the two-stage design removes.
How does it compare to alternatives?
Bladder Botox
Repeatable injection lasting four to nine months versus a permanent implant. Botox requires no surgery and no implant, but needs repeat treatments.
PTNS
Weekly clinic sessions over 12 weeks versus a permanent implant. PTNS is the lower-risk lighter-touch option; SNM has stronger long-term durability for severe cases.
Mr Seth's published research
- Nerve growth factor (NGF): a potential urinary biomarker for overactive bladder syndrome (OAB)?. BJU International (2013).
- The neurological organization of micturition. Handbook of Clinical Neurology (2013).
- Outcomes following percutaneous tibial nerve stimulation (PTNS) treatment for neurogenic and idiopathic overactive bladder. Clinical Autonomic Research (2020).
See all publications.
Frequently asked questions
Why is sacral neuromodulation done in two stages?
The two-stage design is the safety feature of the treatment. Stage 1 places a lead connected to an external stimulator and lets the patient and clinician measure the response, usually over two to four weeks, against a bladder diary. If the response is good, Stage 2 places the permanent stimulator and, where needed, the permanent lead. If the response is not adequate, the lead is removed and the patient avoids a permanent implant on a treatment that would not have worked. The cost is two procedures instead of one.
Is SNM the same as a pacemaker for the bladder?
It is similar in concept and engineering. The implanted pulse generator is comparable in size to a cardiac pacemaker generator and is placed under the skin in the upper buttock. The lead targets a sacral nerve rather than the heart, and the stimulation pattern is different. The everyday experience for patients, a small device under the skin, settings adjusted with a remote programmer, occasional follow-up checks, is broadly the same.
Can I have an MRI after I have SNM?
Modern SNM devices are MRI-conditional, meaning MRI scans can be performed within specified parameters set by the manufacturer. The specifics, full body versus head only, scanner field strength, settings during the scan, depend on the device. This is reviewed before implantation, and the device is matched to the patient's likely future imaging needs. If you have an existing implant, the device card or programmer report will state the current MRI status.
How long does the battery last?
It depends on the device and the stimulation settings. Non-rechargeable devices usually last three to seven years, longer with newer models; rechargeable devices sit towards the top of the three-to-15-year range but need charging weekly or fortnightly (BAUS patient leaflet, 2025). Battery replacement is a smaller second procedure rather than a full re-implant, only the pulse generator is exchanged, the lead is left in place.
Can SNM be removed if I do not want it any more?
Yes. The pulse generator can be removed straightforwardly. The lead can usually be removed too, though leads that have been in place for years can be more adherent to surrounding tissue. Most patients who reach the permanent-implant stage are happy to keep the device, the test phase in Stage 1 is designed to filter out patients who do not benefit before they reach this point.
Is sacral neuromodulation available on the NHS or only privately?
Both. NICE supports SNM for urge incontinence and urgency-frequency (HealthTech guidance 37, formerly IPG64) and idiopathic chronic non-obstructive retention (HealthTech guidance 391, formerly IPG536), and a number of NHS centres provide it for patients meeting the criteria. Private treatment offers shorter waiting times and continuity with the same consultant through the full pathway. Mr Seth assesses patients for SNM at his consulting locations in London.
What if SNM has worked for years and then stops working?
Loss of efficacy can usually be addressed without re-implantation. The first step is reprogramming, adjusting amplitude, frequency or which lead contact is active. If reprogramming does not restore response, lead position is checked and occasionally revised. Battery depletion is excluded by device interrogation. Replacing the whole system is uncommon.
How is the right OAB third-line option chosen?
Botox is repeatable and avoids implants, but carries a small self-catheterisation risk. PTNS is the lowest-risk option but needs a 12-week commitment and ongoing maintenance sessions. SNM is the most durable for severe cases and works for some patients when the others have not, but involves an implant. The consultation is where these are weighed against your priorities, anatomy and previous treatment response.
Further reading
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Private appointments available at Nuffield Health Parkside Hospital, Wimbledon, and other consulting locations across London.
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