Sacral neuromodulation (SNM) is regarded as a 3rd line treatment for patients with overactive bladder (OAB) i.e. after medications and bladder retraining with pelvic floor physiotherapy have been unsuccessful in controlling symptoms.
Patients are regarding as having “refractory” symptoms (i.e. symptoms that are poorly responding to the initial treatments for OAB) when they have not responded to or do not tolerate at least 2 of the newer medications available for OAB symptoms.
What is Sacral Neuromodulation?
Neuromodulation therapy involves the delivery of tiny electrical impulses to nerves in order to change how they work. Sacral neuromodulation (SNM) works by changing how the sacral nerves (originating from the tailbone area) work. These nerves carry messages between the spinal cord and the bladder and their nerve signals are malfunctioning in OAB. Sacral neuromodulation (SNM) interrupts the abnormal signals and helps to improve OAB symptoms.
How does Sacral Neuromodulation work?
The most widely studied form of sacral neuromodulation (SNM) uses the InterStim® device (manufactured by the company Medtronic®). InterStim® works by delivering an electrical message to the sacral nerves which modify abnormal reflexes in the sacral and pelvic nerves that supply the bladder and pelvic floor, as well as modifying abnormal communications between the brain and bladder.
These abnormal reflexes may cause problems with:
- An overactive bladder (OAB) with frequency, urgency and urge urinary incontinence as well as
- Some cases of urinary retention or inability to empty the bladder that are NOT related to blockage in the urinary tract
What does treatment with Sacral Neuromodulation involve?
The InterStim® device works like a pacemaker for the bladder in a similar way that a cardiac pacemaker works for the heart.
Surgery to insert the InterStim® device involves a two staged procedure.
Stage 1 – the trial stage – involves the insertion of a “pacing wire” alongside a sacral nerve using X-ray guidance as a day case procedure.
- If the trial period is successful in reducing urinary symptoms of bladder overactivity (urgency, frequency and urge incontinence) by at least 50%, the patient can proceed to implantation of the full pacemaker device.
- The advantage of the trial stage is the ability to test out the InterStim® device over several days to see if it suits the individual before committing to the treatment.
- About 7 in 10 patients choose to move from the test stimulation to have the permanent InterStim® pacemaker inserted.
Images supplied courtesy of Medtronic Inc.
Stage 2 – the insertion of the permanent InterStim® pacemaker involves the implantation of a device smaller than the size of a box of matches into the fat of the buttock where it cannot be seen.
Images supplied courtesy of Medtronic Inc.
What is involved in the Trial Stage or Stage I Interstim® implant?
The trial stage or Stage 1 InterStim® implant involves a day case procedure under anaesthesia with insertion of a fine wire (using X ray guidance) through the skin over the tailbone (sacrum) which is positioned next to one of the sacral nerves. The fine wire is taped to the skin and covered by surgical dressings so that it is not disturbed for the duration of the trial stage. The wire is connected to the external controller that is worn like a paging device under the clothing for the trial period.
The duration of the trial phase is usually 10 to 14 days. The final pacemaker device is NOT implanted during the trial phase and hence the InterStim® device is controlled during the trial phase by a connection to a temporary external device.
Patients are taught to use the external controller and keep a bladder diary during the trial stage to assess if there is a significant and worthwhile improvement in OAB symptoms.
What is involved in the Permanent Pacemaker or Stage 2 Interstim® implant?
The patient and doctor decide together before the 2nd stage procedure if the InterStim® device has made enough of a difference to symptoms to proceed to the permanent pacemaker implant.
If this is the case, under an anaesthetic a small cut is made in the buttock skin and the pacing wire (inserted during the trial stage) is connected to the permanent InterStim® pacemaker device which is implanted deep to the fat of the buttock.
The device is controlled by a hand held patient programmer (similar in size to a mobile phone) with no external visible wires. Patients are given extensive education in how to use the patient programmer that is usually no more complicated to use than a mobile phone. Usually settings do not need to be changed on a regular basis using the patient programmer.
The InterStim® device is left on continuously and fine-tuning of programmes or settings occurs over the first few months depending on urinary symptoms.
Who is a candidate for treatment with Sacral Neuromodulation?
InterStim® therapy is approved for usage by Medicare in Australia in people older than 18 years of age whose symptoms have not responded to medical and conservative treatments over at least 12 months due to:
- Overactive bladder due to detrusor overactivity or
- Paradoxically also in patients with urinary retention (inability to pass urine or incomplete bladder emptying) which is not due to a blockage in the urinary tract
In Australia InterStim® therapy is also approved for use in some patients with refractory faecal incontinence which has not responded to other treatments.
Who is not suitable for treatment with Sacral Neuromodulation?
InterStim® therapy is not recommended for usage in:
- People in whom the stage 1 trial or test stimulation was unsuccessful
- People who are unable to properly operate the hand held patient programmer
- People with urinary blockage
- Pregnancy
- It is recommended that the InterStim® device be switched off during pregnancy
- People with severe or progressive neurological disorders e.g. Multiple Sclerosis- as it is likely to be less effective than in people with OAB
- People who are likely to need future MRI scans of the spine as the InterStim® device is not currently MRI compatible
- Patients can potentially have limited MRI scans with the InterStim® device in position with the co-operation of the Radiologist for brain MRI and limb MRI scans
InterStim® therapy is NOT intended to treat:
- Symptoms of stress incontinence i.e. loss of urine with cough, sneeze or exercise
- Mechanical blockages in the urinary tract e.g. due to an enlarged prostate or urethral strictures (scarring in the water pipe)
How effective is treatment with Sacral Neuromodulation?
In patients who have a successful trial stimulation and go on to have the permanent implant, studies have shown that between 67 and 87% of patients with urge urinary incontinence have at least a 50% improvement in their symptoms. In some studies half the patients had a 90% or greater improvement in their incontinence symptoms (Cochrane Review of Sacral Neuromodulation 2009).
What is the battery life of the InterStim® device?
The battery life of the InterStim® device depends on exactly which model of device is used and the settings used in the individual patient.
The usual battery life of:
- The InterStim ® I device (larger battery) is between 5 to 9 years
- This device is currently being phased out.
- The InterStim ® II device (smaller battery) is between 3 to 5 years.
Currently the batteries are not rechargeable and the pacemaker device (but not the pacing wire) requires changing as a day case procedure before the battery loses power.
Advantages of treatment with Sacral Neuromodulation
Some of the advantages of the InterStim® device in the treatment of patients with refractory OAB are:
- Its minimally invasive nature
- The ability of the patient to be able to trial the InterStim® device before committing to the therapy
- The lack of potential issues with incomplete bladder emptying and small rate of requiring CISC (clean intermittent self catheterisation) that can occur with treatment of OAB patients with Botulinum toxin
What are potential side effects of treatment with Sacral Neuromodulation?
As with any surgical treatment, potential side effects can occur with the InterStim® device including:
- Pain at the implant site or new pain
- Pain or discomfort related to electrical stimulation
- Infection of the device
- Movement or migration of the pacing lead (thin wire)
- Mechanical problems with the device
- Interactions with other devices or diagnostic equipment such as MRI
- Changes in urinary or bowel function which are undesirable
Most of these problems can be resolved by changes in programming parameters of the InterStim® device.
Some patients with the permanent InterStim® device need reoperation before the pacemaker battery needs replacement due to:
- Reduced or loss of effectiveness of the InterStim® device
- Pain at the lead or pacemaker site
- Infection of the device
It is thought that reoperation rates are reducing over time with refinements in the InterStim® device implantation techniques and equipment.
