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    Role of neurostimulation in urology is on the rise

    The use of neurostimulation in urology has evolved over the years, as new modalities have emerged and new indications are explored. With ongoing research, neurostimulation's role in treating patients with urologic disease will continue to expand, according to one of its long-time practitioners, Kenneth M. Peters, MD. In this exclusive interview, Dr. Peters, chair of urology at Beaumont Hospital in Royal Oak, MI, discusses the various forms of neurostimulation, current research efforts, and potential future uses for this modality. Dr. Peters was interviewed by Urology Times Editorial Consultant Philip M. Hanno, MD, MPH, professor of urology at the University of Philadelphia, Pennsylvania. Dr. Peters is a consultant or researcher for Medtronic, Johnson & Johnson, EMKinetics, and Boston Scientific.

    Q How did you become interested in neurostimulation?


    Kenneth M. Peters, MD
    A My focus on voiding dysfunction goes back to research I conducted as early as residency and continued as an attending. Our department has always been interested in new and novel therapies, and for our more refractory patients with pelvic pain and voiding dysfunction, neuromodulation was certainly an example of this.

    Q What are the current FDA-approved urologic indications for sacral nerve root stimulation, pudendal nerve stimulation, and posterior tibial nerve stimulation?

    A Currently, sacral nerve stimulation is FDA approved for overactive bladder, urgency incontinence, non-obstructive urinary retention, and fecal incontinence. Tibial nerve stimulation is FDA approved for overactive bladder and in Europe is used extensively for fecal incontinence. Pudendal nerve stimulation is a distal branch of the sacral nerve roots, but there are currently no products on the market specifically for this site of stimulation.

    Q Please compare sacral nerve, pudendal nerve, and tibial nerve stimulation.

    A Unfortunately, there have been no head-to-head-to-head trials of these modalities. Sacral nerve modulation using the InterStim device has been around the longest and certainly has the most data.

    We believe that neurostimulation occurs from the nerve to the brain, so the potential benefit of going a little further downstream, like the pudendal nerve, is that you get stimulation through three different sacral nerve roots, which may augment the micturition centers of the brain and improve symptoms. It's been our experience that patients who don't do well with sacral neurostimulation do very well with pudendal; about 90% will respond to pudendal. In my institution's head-to-head trial, patients preferred a pudendal lead using the InterStim device.

    Tibial nerve stimulation using the Urgent PC Neuromodulation System is the new kid on the block. It's been talked about since the 1980s, but it wasn't until recently that randomized, controlled clinical trials were conducted. I see tibial stimulation as a means of opening up neuromodulation to the masses—to all those patients who don't get better with drugs and behavioral therapies.

    Q In the treatment of overactive bladder, how do you compare neurostimulation to other forms of treatment?


    PHILIP M. HANNO, MD, MPH
    A Overall, I'm pretty disappointed by the drugs available. We're all looking for something new to offer our patients. Drugs help a component of patients, but if you look at the data, 80% of patients stop drugs within a year. I'm looking for something beyond that, and that's where I think neurostimulation has a role.

    Neurostimulation is not offered enough to patients. Those of us who do it offer it frequently and early in the course of the disease. That's where it really impacts the patient's quality of life.

    Q What is the place of neurostimulation in nonobstructive retention?

    A The most common treatment for nonobstructive retention is intermittent catheterization. There are very good data showing that neurostimulation can be beneficial for idiopathic nonobstructive retention. This is quality of life driven, so if a patient really wants to get off the catheter and there are no medications that make them better, neurostimulation is the next step. Sacral neuromodulation is the form of neurostimulation that has been studied the most and is FDA approved for this indication.

    Q What has your success rate been for that?

    A It's variable, because predicting the underlying cause of nonobstructive retention is difficult. It seems to work best in patients with high tone pelvic floor dysfunction. I usually tell patients with nonobstructive retention that there is a 50% to 60% success rate. For overactive bladder, I put the success rate at 85% or 90%.

    Q What do you see as the role of neurostimulation in interstitial cystitis?


    KENNETH M. PETERS, MD
    A There have been a number of studies, including some that we've done, looking at neurostimulation for the treatment of interstitial cystitis. However, predicting pain relief as a response to neurostimulation is difficult. I tell patients with interstitial cystitis that I can treat their urgency and frequency symptoms with neurostimulation and that improvement in their pain is an added bonus. If they understand that their urgency/frequency may get better but their pain may persist, then it's worth a try. That being said, some interstitial cystitis patients see a remarkable improvement in pain.

    Q In the future, do you see any other disorders that neurostimulation might be useful for treating?

    A There's a host of disorders that neurostimulation can treat. Sacral neuromodulation was approved for treating fecal incontinence earlier this year. Other possibilities include irritable bowel syndrome, sexual dysfunction, erectile dysfunction, and pain disorders such as vulvodynia or orchalgia.

    I think the indications are going to continue to expand. It's just a matter of determining the right nerve and the best settings.

    Q Can you comment on direct chronic pudendal nerve stimulation as a viable alternative to failed sacral nerve stimulation?

    A We've had a lot of experience with pudendal nerve stimulation. It came about because for some patients, behavioral therapy, physical therapy, drugs, and sacral neuromodulation didn't work. I was frustrated that there wasn't something else to offer patients, so we pursued the pudendal nerve because there had been earlier animal studies suggesting that the pudendal nerve was a good inhibitory nerve to the bladder.

    The question was, how do you get a lead to the nerve and how do you know you've reached the nerve? At our center, we developed a technique and did a comparative trial in which the patients had sacral and pudendal electrodes put in as part of a staged approach. The patients stimulated each one for a week. They were randomized to which one would get started first, and they kept diaries and questionnaires on both. When we asked the patients which lead they felt was superior, 79% chose the pudendal, compared with 21% for the sacral. That seemed to suggest that the pudendal lead is better. We then implanted the pudendal leads and published chronic studies that showed good durability. It's a great salvage procedure and could easily be a primary area of stimulation.

    Q What are some of the current research efforts that you're involved with?

    A We're doing a lot of research in neurostimulation. One of those efforts involves sacral neuromodulation, for which we've created a prospective database with hundreds of patients. We're mining that database to look at different factors such as efficacy based on patient age, whether you need motor or sensory or both to achieve success, what the revision rate is, the impact on sexual and bowel function, and so on. That's an ongoing project.

    We're also working on new types of stimulation like magnetic stimulation. One study we're conducting involves tibial nerve stimulation using magnetic energy, as opposed to electrical energy. The preliminary data look promising and there is currently a sham-controlled trial ongoing. We're also involved in trials of different technologies such as patch technologies, in which electrical current is delivered through the skin to the nerve.

    Q What other neurostimulation techniques do you see in the future? For example, could we be looking at a special shoe, boot, or sock that patients could wear percutaneously that would stimulate them all the time?

    A I've heard people joke about a "Nike dry" shoe. That would suggest that you could cutaneously get to a nerve and impact the bladder, and the evidence doesn't exist yet that that's the case. We need more research to know if something like that is feasible.

    However, at the tibial nerve, if it was possible to place a small electrode or microstimulator under the skin that would route the energy to the nerve, you could then stimulate the nerve on demand.

    Currently, tibial neurostimulation is performed once a week for 30 minutes because that's been the dogma. But what if you did 30 minutes twice a week or three times a week or every day? Would the response be more robust? There's just so much we don't know about it.

    Q One of the problems with neurostimulation is the front-loaded expense. Do you see any less expensive forms of neurostimulation therapy emerging?


    KENNETH M. PETERS, MD
    A I'm surprised that there's only one company that makes an implantable device. We need competition in the marketplace. It's a hard area for companies to get into because the upfront cost of developing a neuromodulation device is very high.

    That being said, tibial nerve stimulation is more cost effective in the long run than having an implantable device if you can get good efficacy and maintain it over time. We showed at the 2011 AUA annual meeting that 97% of patients undergoing tibial nerve stimulation maintained an improvement at 24 months with one treatment per month. The question is, in the long term, are patients going to continue to come to the office for a treatment?

    I think the future is microstimulators, which are small implanted devices that may have an internal or external energy source. There are a number of companies looking at those, and by having microstimulators that have rechargeable batteries that can last up to 20 years, you may be able to control the cost of the technology.

    Q Do you see costs diminishing for neurostimulation devices in the long run?

    A Costs have to diminish over time, but it's going to be driven by the skill of the implanter, the marketplace, and device makers. The closer a lead is placed to a nerve, the less energy needed to stimulate the nerve, the longer the battery life, and the lower the cost. However, real cost savings will come once we have more competition in the marketplace. I hope that will change, because it needs to be opened up to more patients.

    Q In the near future, do you see any competition for making neurostimulation devices?

    A There are companies that I'm involved with that are working on these devices, but I don't think anyone is close to coming to market. It is a long process. The biggest competition out there is going to be tibial nerve stimulation since it has a CPT code now.

    Q Do you think transcutaneous electrical nerve stimulation has a future or could be made more effective given what we now know about neuromodulation?

    A The issue with transcutaneous stimulation is that you have to be able to deliver enough energy to the nerve but also keep the cutaneous collateral stimulation under control. That's been the limiting factor; people can't tolerate the sensation on the skin to get to the nerve.

    There are new technologies being developed that change waveforms and allow the energy to penetrate through the skin and reach the nerve via cutaneous stimulation. That's a source of ongoing research, and I think it is something we may be seeing more of in the future.

    Q Do we know much more about how neurostimulation works now than we did 20 years ago, or is there still a void?

    A There is still a void. We understand a little bit more than we did. In the simplest terms, initially, it was seen as: We're stimulating the nerve, so it has a direct effect on the bladder. But more and more, the data suggest that it has more of a central effect.

    Some of the work from Dr. Clare Fowler's lab on Fowler's syndrome showed relative inactivity in the brain centers. When they added neuromodulation or turned on the sacral nerve stimulator, those areas that should be active began to light up. Then, when the bladder was filled while stimulating the sacral nerve, it pretty much normalized. It seems like neuromodulation is probably working more in the micturition center of the brain, and that's why increasing afferent signals may be a good thing.

    When patients ask how it works, I tell them it overrides the abnormal signals that the nerve is getting and gives it the signal it needs for the bladder to work the way it should.

    Q Do you think neuromodulation therapy is related in any way to acupuncture?

    A No, because acupuncture doesn't stimulate nerves; it works more on energy pathways. Although some of the meridians may be the same, they're totally different concepts.

    Q Is there anything you would like to add?

    A Most of what we've been talking about is related to the bladder, but neuromodulation could help with erectile dysfunction as well. We have done some studies looking at stimulation of the cavernous nerve acutely during a perineal prostatectomy and have shown that it creates tumescence and rigidity. In the future, the idea would be to implant a cuff electrode at the cavernous nerve through a perineal incision and possibly tunnel it to the scrotum with an implantable small microstimulator, which could be done in an hour. Then patients would be given a remote control to control their erections. My hope is that this could be a more minimally invasive way to treat ED than a penile prosthesis.

    Philip M. Hanno, MD, MPH
    Philip M. Hanno, a Urology Times editorial consultant, is professor of urology at the University of Pennsylvania, Philadelphia.

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