Sacral Neuromodulation: The Choice is Yours

In Sacral Neuromodulation therapy, we stimulate the nerve that controls the bladder in order to treat several types of problems. These include symptoms of Overactive Bladder (OAB) including urinary frequency, urgency and urgency incontinence. SNM can also be used to treat fecal incontinence and urinary retention. Sacral neuromodulation works by stimulating nerves to the pelvis that control these functions. But why do you need to undergo a test of stimulation before having the device implanted permanently?

Testing is Necessary

A SNM device has two components that can be separated: a lead which is the wire that sits next to the nerve and a generator that controls the stimulation and contains the battery that powers the signal. One way to test the therapy before permanently implanting the device is to place the permanent lead next to the nerve but connect it to a temporary battery that is worn in a pouch around your waist. The other way of testing is to place one or two temporary wires next to the nerves and connect those wires to the temporary battery. Either way, some sort of testing is required. The generator is meant to provide therapy for many years and there is no reason to implant this in you unless we are sure that the therapy will be a success.

What is Success?

Success with Sacral Neuromodulation is often defined as at least 50% improvement in symptoms, whether that is trips to the bathroom, episodes of incontinence or the number of times that you need to catheterize each day. Some patients will see far greater than 50% improvement. Also, you need to be satisfied with the therapy, even if it meets the 50% requirement, for it to be successful. Unfortunately, not every patient will respond to this therapy. Without testing ahead of time, there is no way to reliably predict who will have satisfactory improvement. There is no other way for us to know who will improve enough to proceed with the therapy permanently. This is the reason that we first test the therapy.

There are two ways of testing sacral neuromodulation prior to permanent implantation. One type of testing is called a peripheral nerve evaluation (PNE) or basic evaluation and can be performed in the office without sedation. A second form of testing is a staged evaluation or advanced evaluation. This is performed in an operating room usually under sedation or general anesthesia. In both types of testing the goal is to find out how well you will respond to and tolerate the therapy before a permanent patient generator is placed. Both types of tests are used and you are free to choose which type you think is best for you. However, there may be some reasons to choose one test type over the other that are not immediately obvious to you. It can be helpful to explore what is involved with each type of test and how the advantages and disadvantages of each may impact your decision.

Peripheral Nerve Evaluation

In a peripheral or basic evaluation one or two tiny, temporary wires are placed alongside the nerves, instead of the permanent lead. Basic evaluations do not have to occur in the operating room and most patients do not need any sedation. You can usually drive yourself home after the procedure. Instead of sedation or general anesthesia, a numbing medicine is injected to prevent pain with the procedure. Since the permanent lead is not placed, there are no incisions needed. Needles are placed under the skin into the natural openings in the sacrum, where the nerves can be found. The wires can are then threaded through the center of the needles to be placed next to the nerves.

In peripheral nerve evaluations, we usually place the wires on both sides to test both the right and left nerves. In staged evaluations it is customary to place just one lead on whichever side gives the best response. The wire placed for peripheral testing is not as well anchored as the permanent lead so the testing is usually for a shorter time, about a week or less. During the test, you and your doctor will discuss how your symptoms are responding to the stimulation. If your symptoms are improving, you may not make any changes. If you are not seeing improvement, you may try stimulating on the opposite side or adjusting how high the stimulation is set. Keeping track of your symptoms in a diary can be useful to see any changes. At the conclusion of the testing, the wires are easily removed by simply pulling them out. Patients who see satisfactory improvement during the testing can go on to have both the permanent lead and the generator implanted in the operating room in a single session.

One of the most important points to make about peripheral nerve evaluation is that if you do not see satisfactory improvement during PNE, it does not mean that your symptoms are not going to respond to Sacral Neuromodulation. In fact, people who see incomplete response to the basic testing, will often find that if they next undergo a staged test, they may actually have a good response to SNM therapy. Basic evaluations can be a good way to test SNM without first going to the operating room but are not as accurate as advanced evaluations. So, if you are not improved during a PNE, you should strongly consider having a staged test.

Staged Testing

In staged or advanced testing of sacral neuromodulation, the permanent lead is placed under the skin next to the nerve but the generator is not placed at that time. Instead, the lead is connected to a very thin wire that exits the skin and is attached to a small temporary battery that you wear in an elastic belt around your waist. This allows you to test the therapy for multiple weeks without having the patient generator implanted. The lead is usually placed while you are under anesthesia, either sedation or general anesthesia (I prefer to place these under general anesthesia in my patients). You will need someone to drive you home after the procedure. During advanced testing, since the permanent lead is being placed, there are small incisions made over the sacrum and over the buttocks.

In staged testing, though, you may have both sides tested, the lead is usually placed on one side or the other, depending on where you see the best response. Because the lead placed in the advanced test is designed to be permanent, you are able to be tested for a longer time if needed, up to several weeks. Just as with basic testing, you and your doctor will discuss your response to determine if you should have the generator placed. If your results are satisfactory and you are pleased with the therapy, the generator is implanted and attached to the permanent lead. The generator is placed in a second procedure in the operating room, though often you will not need as much sedation for this. If you have not seen satisfactory improvement, all of the parts of the neuromodulator are completely removed at the conclusion of the unsuccessful test.

Making Your Choice

Both PNE and staged testing are excellent options for determining if SNM provides enough improvement for you to permanently implant a device. But there are considerations that may help you determine which is best for you. It is helpful to begin by thinking of staged testing as the standard form of testing. It is the most reliable in identifying everyone who should have a permanent implant. But it requires sedation or general anesthesia in the operating room. By contrast, PNE offers a “short-cut” for some patients allowing them to find out if neuromodulation is effective without undergoing anesthesia. Permanent implant of sacral neuromodulation will always require a trip to the operating room, but patients with a successful PNE will have both components, the lead and the generator, implanted in one trip.

But this needs to be balanced against the risk the you may not see improvement with PNE and will still need a staged test to see if SNM is right for you. Those patients with an inconclusive PNE will ultimately undergo three procedures, not two. This is why some patients decide to proceed straight to staged testing. Both types of testing have their advantages.

Special Circumstances

In my experience, there are some special circumstances that may encourage patients to consider staged testing over PNE testing. First, patients who would have difficulty lying on their stomach for an extended period may prefer staged testing, which can be performed while you are asleep. Placing wires for PNE testing can often be done quite quickly, but in some patients it can take longer to place them in optimal positions. If you are unable to tolerate being on your stomach for up to 30 minutes, PNE could be difficult for you. Most patients tolerate PNE testing quite well, however.

The PNE testing period is typically shorter, often a week or less. For most patients, this is enough time to determine a response. However, If you have fecal or urinary incontinence that occurs only every few days, it may take longer than a wee to determine if you are experiencing a significant reduction in symptoms. In addition, there are some providers who feel that urinary retention patients also benefit from a longer period of testing. There are early indications that a new PNE lead may be able to test beyond 7 days, allowing this type of testing to be used in those situations. However, the manufacturer of the PNE test device still recommends only a 7-day trial and there is little evidence to guide us on testing beyond this interval for this new version.

Lastly, I always ask my patients who are having trouble deciding between PNE and staged testing what they would plan to do if PNE testing was inconclusive. If patients would not consider staged testing if they saw no response with PNE testing, I recommend that they proceed straight to staged testing. Otherwise, there is too much of a risk that they will miss an opportunity to have a successful therapy if the PNE is indeterminate.

Until relatively recently, you would have had little choice about your neuromodulation battery. For most of their history, SNM batteries were not rechargeable. The battery slowly discharged over several years until it was replaced. Only the battery needed replacement and the existing lead remained in place. Today, rechargeable batteries are available. These new generators have advantages and disadvantages that may be more relevant to some people than others. The rechargeable devices are still a relatively new technology, so we have limited data to guide us as to which device is best for any individual person. But based on the studies available, both of sacral neuromodulators as well as other rechargeable devices, we can offer some guidance as you decide which type of neuromodulation devices is right for you.

The evolution of SNM batteries over the last 20 years has progressed toward smaller battery size. The goal has been to create a more comfortable and less intrusive therapy. But there is a balance to strike because as battery size decreases, the capacity and the longevity of the battery decreases as well. Make a recharge-free battery small enough, and it won’t last long enough to be of much use. The application of rechargeable technology to sacral neuromodulators, eventually produced an ultra-small battery that can be useful over a much longer time.

Rechargeable SNM generators are able to be quite small – the latest device is 80% smaller and 1/3 the weight of the current recharge-free device. The generator is less than 1 inch wide by 2 inches long. There are likely advantages to such a diminutive implant, though with a relatively short history we can’t know with certainty. Both types of SNM generators are buried in the fat of the buttocks to minimize discomfort. Most people won’t even notice either type of battery beneath their skin. But very thin patients may not have enough fat, even in the buttocks, to easily bury a standard SNM generator. For these patients, a very small device might decrease the risk of discomfort and reduce the noticeability of the SNM. I would like to note here that pain at the generator site is reported in only about 7% of patients, so the advantage of a small battery may not apply to most people. But, if you are very thin or have a history of pain from a previous or current neuromodulator, size may be an important consideration. 

Is Smaller Always Better?

Could there be disadvantages to small generator size? Again, with a relatively short history to these rechargeable batteries, we can only make predictions based on how patients have responded over a couple of years. However, it has been suggested that the small size might make the devices more difficult to locate. For obese patients, locating even the larger recharge-free device can be a challenge. But an advantage of the recharge-free generator in these patients is that they only need to locate the device occasionally when they want to change a program or run a check on the device. Patients with rechargeable neuromodulators will need to locate their devices much more frequently. This should not be an issue for most patients using rechargeable SNM. However, for those who may be obese, have limited use of their hands or have trouble reaching behind to where the device is located, this is a potential issue that should influence their decision.

Another potential problem might be somewhat surprising. Some patients have a tendency to move their generators around through the skin. This is common enough to have a name and it’s called “Twiddler’s Syndrome”. This is a funny name for a not-so-funny problem because twisting the device like this can cause it to spin around and eventually break. It has been suggested that the smaller devices could be more likely to spin in these twiddler patients. Though this is completely hypothetical, it is nonetheless interesting to ponder. 

An important advantage for rechargeable devices is the longevity or life of the battery. Recharge-free devices eventually discharge and need to be replaced, though this can be done fairly easily under a local anesthetic. Current recharge-free devices are rated for a longevity of 5-6 years at standard patient settings. Rechargeable devices, on the other hand, can probably be used for 15 years or more. A limit for any rechargeable battery in any device is fading. Think about your smartphone battery. Over hundreds of charging cycles, does it still hold a charge as well? It would be a real problem if your sacral neuromodulator generator had as much trouble holding a charge after a few years as your smartphone. The loss of recharge capacity of the battery over time is called cycle-fading. The most current SNM device, however, is essentially immune to cycle-fading because it does not use a traditional lithium-ion battery. The new rechargeable battery technology also appears to resist the loss of capacity that occurs over time that is independent of the number of charge cycles (called calendar fading). Thus, at its rated 15-year lifespan, the newest rechargeable devices are expected to show no decrease in their ability to recharge to their full capacity. The manufacturers make no specific claims beyond 15 years. However, it is possible that these new generators may continue to function adequately even beyond that predicted lifespan.

Lifespan of Recharge-Free Devices

Though a lifespan for the recharge-free generator is often quoted as 5-6 years, it may be possible for this interval to be longer in at least some patients (as well as shorter in others). There are a couple of developments that may allow these devices to remain useful well beyond that range. As experienced implanters become better and better at lead placement (called lead optimization), the lead can be placed closer to the nerve with more options for how we stimulate. With lead optimization, we are able to treat patients with lower and lower levels of energy. The less energy used to signal the nerve, the longer the battery will last. 

The second reason why recharge-free generators may have utility beyond 5-6 years is suggested by recent studies on the amplitude or “volume” of stimulation. Traditionally, when adjusting the stimulation of the sacral neuromodulator in a patient, the amplitude was increased until patients were just able to feel the stimulation to the nerve. The point at which you first begin to sense the signal is called the sensory threshold. In the past, people were told to maintain their stimulation near the level of sensory threshold. But over the years, it was noted that many people who were not feeling any sensation of nerve stimulation still had an acceptable response to therapy. The results of a recent clinical trial I was involved with suggest that, early in therapy, people who are stimulated at as little as half of sensory threshold still see similar benefits as those who have the therapy turned up to to a level that they can feel it. If future studies confirm this finding over a longer time, it could lead to lower stimulation levels, considerably increasing the life of recharge-free batteries. Between improvements in how well we place leads and possible decreases in the necessary level required for successful stimulation, we may find that even recharge-free SNM may last for many years.

Therapy Over Time

Whenever I discuss the longevity of rechargeable versus recharge-free devices with patients, I am always concerned that they may misinterpret battery longevity as meaning they are guaranteed to be free from any further surgery for at least 15 years. It is certainly fair to say that some patients who have placement of a rechargeable generator will experience successful therapy without a return to the operating room for 15 or more years. However, not all patients will see this benefit and it is probably fair to say that the majority of patients will not experience satisfactory therapy without any further neuromodulation procedures for 15 years. 

The first issue is that there is so much that can happen to a patient over a 15-year treatment period. As they age, some patients may have changes in memory and thinking that would make it difficult to remember to charge the device on a regular basis. Someone who could easily place the charging pad over their device at age 70 may have more difficulty at 80 or 85. Switching to a recharge-free device because a patient is no longer able to reliably maintain their rechargeable device could be problematic because a new lead would also have to be placed, under anesthesia. 

Though a rechargeable battery may last 15 years, a sacral neuromodulator includes both a generator and a lead. Issues other than running out of charge can occur with generators and problems can also arise with the lead. In a study of over 300 SNM device implants, 38% of patients had to undergo a replacement of the lead at an average of 7 years. The same analysis also found that, over the same time, 39% of patients had dropped out of the study for a number of reasons including device infection, malfunction of the device or lack of response. So, while a generator that will last at least 15 years sounds like the only choice, many patients, unfortunately, will not see a full 15-year benefit from a rechargeable sacral neuromodulator. This should not discourage you from considering this type of neuromodulator but can help to inform your decision. 

Patient Commitment

A final consideration when contemplating recharge versus recharge-free neuromodulation is the amount of patient maintenance of the device necessary for each. Recharge-free devices have sometimes been thought of as a low-maintenance therapy. After 6-12 weeks, further adjustment of the stimulation is usually unnecessary. Many patients can go for years without adjusting their settings. However, I am reluctant to endorse the “set it and forget it” mindset. While recharge-free neuromodulation may not require frequent adjustment, I always emphasize that Overactive Bladder, Fecal Incontinence and Urinary Retention are life-long diseases that require lifetime therapies. Neuromodulation therapy is always more successful when patients and their doctors maintain a continued commitment to additional measures including behavioral therapies like diet changes and fluid moderation. We may spend less time managing the device with a recharge-free neuromodulator, but we never stop managing the disease. 

Regardless of how you view long-term therapy, it is clear that rechargeable devices will always require more patient commitment to the device due to the need for regular charging. The time burdens for charging are not excessive with the latest device able to be charged weekly in about 20 minutes or reaching a full charge that can last two weeks in less than an hour. This regular interaction with the device could have varying effects on each individual. I could imagine some patients who would find reassurance and comfort from regularly charging their device. It may give them a sense of control and empowerment to be an active participant in their therapy. It could even be a regular reminder to stick with the behavioral therapies that can make sacral neuromodulation even more effective. 

However, one can also envision patients who do not want to be frequently reminded of their dependence on neuromodulation. The charging pad for rechargeable devices is fairly convenient and allows patients to move around freely even while charging. But some patients may find even this minimal burden to be bothersome. This is suggested by data on rechargeable spinal cord stimulators. In these studies, patients with a rechargeable stimulator were more likely to terminate therapy early than those with a recharge-free device. In one of these studies, but not in others, there is an indication that patients older than age 74 may be less satisfied with rechargeable devices than those under 56. 

Making Your Decision

For some, the decision to proceed with sacral neuromodulation may be an easy one. After suffering for years with Urinary Incontinence or Fecal Incontinence or Urinary Retention, you may be relieved to have finally found a potentially successful treatment. But the choice to use a recharge-free versus a rechargeable generator may not be as simple. It may help to first focus on patients who are likely to see the most benefit from a rechargeable device. This includes patients who are extremely thin, have a prior history of pain at a generator site or have a desire to be very active in their therapy. There are patients who are at a high risk for complications, such as infection, with generator replacement. Occasionally, patients will require very high stimulation energy that would quickly drain a recharge-free battery. All of these patients may see enough benefit from a rechargeable battery that the choice is an easy one. 

Other patients may have a high likelihood of problems with a rechargeable generator or may see more benefit from a recharge-free device. This could include patients who are very obese or have limited dexterity of their hands, making it difficult to regularly place the charging pad over their neuromodulator. Patients with problems of thinking and memory or who are at risk of having such problems in the next 15 years may gravitate toward a recharge-free device. Anyone who is anxious about frequently interacting with their device, has difficulty with technology or has trouble keeping up with previous therapies may want to avoid a rechargeable device that requires a considerable patient commitment. Based on limited data, those in their 60’s or 70’s may be more dissatisfied with a rechargeable than those who are much younger. Other factors such as frequent travel or a busy lifestyle are not so clear as to whether how much they should be taken into consideration. 

Choosing between a recharge-free or rechargeable sacral neuromodulator seems to present a challenge. But it is reassuring to remember that, in many ways, we are fortunate to be in a position to even choose. For over 20 years, patients who wanted the considerable benefits that can come from SNM had no choice. Their only option was the recharge-free device. But our days of having only a single option for neuromodulation are over. Now, patients are free to consider the pros and cons of both types of device and choose the best one for them. This is less a dilemma than an opportunity.