Neuromodulation for Neuropathic Pain Syndromes With Dr. Prasad Shirvalkar
For certain diagnoses and patients who meet clinical criteria, neuromodulation can provide profound, long-lasting relief that significantly improves quality of life. In this episode, Aaron Berkowitz, MD, PhD, FAAN speaks with Prasad Shirvalkar, MD, PhD, author of the article “Neuromodulation for Neuropathic Pain Syndromes,” in the Continuum® October 2024 Pain Management in Neurology issue. Dr. Berkowitz is a Continuum® Audio interviewer and a professor of neurology at the University of California San Francisco in the Department of Neurology and a neurohospitalist, general neurologist, and clinician educator at the San Francisco VA Medical Center at the San Francisco General Hospital in San Francisco, California. Dr. Shirvalkar is an associate professor in the Departments of Anesthesia and Perioperative Care, Neurological Surgery, and Neurology at Weill Institute for Neurosciences at the University of California, San Francisco in San Francisco, California. Additional Resources Read the article: Neuromodulation for Neuropathic Pain Syndromes Subscribe to Continuum: shop.lww.com/Continuum Earn CME (available only to AAN members): continpub.com/AudioCME Continuum® Aloud (verbatim audio-book style recordings of articles available only to Continuum® subscribers): continpub.com/Aloud More about the American Academy of Neurology: aan.com Social Media facebook.com/continuumcme @ContinuumAAN Host: @AaronLBerkowitz Guest: @PrasadShirvalka Full episode transcript available here Dr Jones: This is Dr Lyell Jones, Editor in Chief of Continuum, the premier topic-based neurology clinical review and CME journal from the American Academy of Neurology. Thank you for joining us on Continuum Audio, which features conversations with Continuum's guest editors and authors, who are the leading experts in their fields. Subscribers to the Continuum Journal can read the full article or listen to verbatim recordings of the article and have access to exclusive interviews not featured on the podcast. Please visit the link in the episode notes for more information on the article, subscribing to the journal, and how to get CME. Dr Berkowitz: This is Dr Aaron Berkowitz, and today I'm interviewing Dr Prasad Shirvalkar about his article on neuromodulation for painful neuropathic diseases, which appears in the October 2024 Continuum issue on pain management in neurology. Welcome to the podcast, and if you wouldn't mind, please introducing yourself to our listeners. Dr Shirvalkar: Thanks, Aaron. Yes, of course. So, my name is Prasad Shirvalkar. I'm an associate professor in anesthesiology, neurology and neurological surgery at UCSF. I am one of those rare neurologists that's actually a pain physician. Dr Berkowitz: Fantastic. And we're excited to have you here and talk to you more about being a neurologist in in the field of pain. So, you wrote a fascinating article here about current and emerging neuromodulation devices and techniques being used to treat chronic pain. And in our interview today, I'm hoping to learn and for our listeners to learn about these devices and techniques and how to determine which patients may benefit from them. But before we get into some of the clinical aspects here, can you first just give our listeners an overview of the basic principles of how neuromodulation of various regions of the nervous system is thought to reduce pain? Dr Shirvalkar: Yeah, I would love to try. But I will promise you that I will not succeed because I think to a large extent, we don't understand how neuromodulation works to treat pain, to describe or to define neuromodulation. Neuromodulation is often described as using electrical stimuli or a chemical stimuli to alter nervous system activity to really influence local activity, but also kind of distant network activity that might be producing pain. On one level, we don't fully understand how pain arises, specifically how chronic pain arises in the nervous system. It's a huge focus of study from the NIH Heal Initiative and many labs around the world. But acute pain, which is kind of when you stub your toe or you burn your finger, is thought to be quite different from the changes over time and the kind of plasticity that produces emotional, cognitive and sensory dimensions. Really what I think is its own disease, chronic pain, of which there are multiple syndromes when we use neuromodulation, either peripheral nerve stimulation or electrical spinal cord stimulation. One common or predominant theory actually comes from a paper in science from 1967 and people still use it, foundational theory and it's called the gate control theory. Two authors, Melzack and Wall, postulated that at the spinal level, there are, there's a local inhibitory circuit or, you know, there's a local circuit where if you provide input to either peripheral nerves or either spinal cord ascending fibers that to kind of summarize it, there's only so much bandwidth, you know, that nerves can carry. And so that if you literally pass through artificial signals electrically, that you will help gate out or block natural pathological but natural pain signals that might be arising from the periphery or spinal cord. So, you know, one idea is that you are kind of interfering with activity that's arising for chemical neuromodulation. The most common is something known as intrathecal drug infusion drug delivery ITTD for that we quite literally put a catheter in the spinal fluid, you know, at the level of the dorsal horn neurons that we think are responsible for perpetuating or creating the pain. Where's the pain generator? And you really, you can infuse local anesthetic, you can infuse opioids. And what's nice is you avoid a lot of systemic side effects and toxicity because it goes right to the spinal cord, you know, by infusing in the fluid. So there's a couple of modalities, but I will say just, like maybe all of our living experience, pain is in the brain. And so, we don't really understand, I would say, what neuromodulation is doing to the higher spinal or brain levels. Dr Berkowitz: Fascinating topic. And yeah, very interesting to hear both what our current understanding is that some of our current understanding is based on data that's 60 years old and that we're actually probably learning about pain by using these modulation techniques, even though we don't really understand how they might be working. So interesting feedback loop there as well as in as in the as in this land. So, your article very nicely organizes the neuromodulation techniques from peripheral to central. So, encourage our listeners to check out your article. And first before we get into some of the clinical applications, just to give the listeners the lay of the land, can you sort of lay out the devices and techniques available for treating pain at each level of the neuroaxis? We'll get into some of the indications in patient selection in a moment, but just sort of to lay out the landscape. What's available that you and your colleagues can use or implant at different levels when we're thinking of referring patients too? Dr Shirvalkar: Absolutely. So, starting from the least invasive or you know, over the counter patients can purchase themselves a TENS machine. Many folks listening to this have probably tried a TENS machine in the past. And the idea is that you put a couple of pads, at least two. So you have like a dipole or you have a positive and a negative lead and you basically inject some current. So, the pads are attached to a battery and you can put these pads over muscle. If you have areas where myofascial pain or sore muscles, you can put them, frankly, over nerves as well and stimulate nerves that are deeper. Most TENS machines kind of use electrical pulses that occur at different rates. You change the rates, you can change the amplitude and patient can kind of have control for what works best. Then getting slightly more invasive, we can often stimulate electrically peripheral nerves. To do this we implant through a needle, a small wire that consists of anywhere from one electrical contact to four or even eight electrical contact. What I think is particularly cool, like TENS, which is transcutaneous electrical nerve stimulation that goes through the skin. Peripheral nerve stimulation aims to stimulate nerves, but you don't have to be right up against the nerve. So, yeah. We typically do this under an ultrasound and you can visualize a nerve like the sciatic nerve, peroneal nerve, or you know, even if someone has an ulnar or a neuropathy, you know, that's the compression. There's a role obviously for surgery and release, but if they have predominantly pain, it's not related to a mechanical problem per se, you could prevent a wire from a peripheral nerve stimulator as far as one centimeter from a nerve and it'll actually stimulate that that modulated and then, you know, kind of progressing even more deeply. The spinal cord stimulation, SCS, it's probably the most ubiquitous or popular form of neuromodulation for pain. People use it for all kinds of diseases. But what it roughly involves is a trial period, which is a placement of either two cylindrical wires, not directly over the spinal cord, but actually in the epidural space, right? So, it's kind of like when you get an epidural injection or doing labor and delivery, when women get epidural catheters, placing spinal cord stimulator leads in that same potential space outside the dura, and you're stimulating through the dura to actually target the ascending dorsal column fibers. And so, you do a trial period or a test drive where the patients get these wires put in. They're coming out of the skin, they're connected to a battery, and they walk around at home for about a week, take careful notes, check in with them, and they keep a diary or a log about how much it helps. Separately. I will say it's hard to distinguish this, the placebo effect often, but you know, sometime