Show notes
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 clinical neurology at the University of California, San Francisco 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, sometimes we want to use the placebo effect in clinical practice, but it is a concern, you know, with such invasive things. But you know, if the trial works well, right, you basically can either keep the leads where they are and place a battery internally. And it's for neurologists. You're familiar with deep brain stimulation. These devices are very similar to DVS devices, but they're specifically made for spinal cord stimulation. And there's now like seven companies that offer manufacturers that offer it, each with their own proprietary algorithm or workflow. But going yet more invasive, there is intrathecal drug delivery, which I mentioned, which involves placement of the spinal catheter and infusion of drug into spinal fluid. You could do a trial for that as well. Keep a patient in the hospital for a few days. You've all probably had experience with lumbar drains. It's something real similar. It just goes the other way. You know, you're infusing drugs, and it could also target peripheral nerves or nerve roots with catheters, and that's often done. And last but not least, there's brain stimulation. Right now, it's all experimental except for some forms of TMS or transcranial magnetic stimulation, which is FDA approved for migraine with aura. There are tens machine type devices, cutaneous like stimulators where you can wear on your head like a crown or with stickers for various sorts of migraines. I don't really talk about them too much in in the article, but if there's a fast field out there for adjunctive therapy as well, Dr Berkowitz: Fantastic. That's a phenomenal overview. Just so we have the lay on the land of these devices. So, from peripheral essentially have peripheral nerve stimulators, spinal cord stimulators, intrathecal drug delivery devices and then techniques we use in other areas of neurology emerging for pain DBS deep brain stimulation and TMS transcranial magnetic stimulation. OK let's get into some clinical applications now. Let's start with spinal cord stimulators, which - correct me if I'm wrong - seem to be probably the most commonly seen in practice. Which patients can benefit from spinal cord stimulators? When should we think about referring a patient to you and your colleagues for consideration of implantation of one of these spinal cord stimulator devices? Dr Shirvalkar: So, you know, it's a great question. I would say it's interesting how to define which patients or diagnosis might be appropriate. Technically, spinal cord stimulators are approved for the treatment of most recently diabetic peripheral neuropathy. And so, I think that's a really great category if you have patients who have been failed by more conservative treatments, physical therapy, etcetera, but more commonly even going back, neuropathic low back pain and neuropathic leg pain. And so, you think about it and it's like, how do you define neuropathic pain. Neuropathic pain is kind of broadly defined as any pain that's caused by injury or some kind of lesion in the somatosensory nervous system. We now broaden that to be more than just somatosensory nervous system, but still, what if you can't find a lesion, but the pain still feels or seems neuropathic. Clinically, if something is neuropathic, we often use certain qualitative descriptors to describe that type of pain burning, stabbing, electric light, shooting radiates. There's often hyperpathia, like it lingers and spreads in space and time as opposed to, you know, arthritis, throbbing dull pain or as opposed to muscle pain might be myofascial pain, but sometimes it's hard to tell. So, there aren't great decision tools, I would say to help decide. One of the most common syndromes that we use spinal cord stimulation for is what used to be called failed back surgery syndrome. We never like to, we now try to shy away from explicitly saying something is someone has failed in their clinical treatment. So, the euphemism is now, you know, post-laminectomy syndrome. But in any case, if someone has had back surgery and they still have a nervy or neuropathic type pain, either shooting down their legs and often there's no evidence on MRI or even EMG that that something is wrong, they might be a good candidate, especially if they're relying on long term medications that have side effects or things like full agonist opioids, you know that that might have side effects or contraindication. So, I would say one, it's not a first line treatment. It's usually after you've gone through physical therapy for sure. So, you've gone through tried some medications. Basically, if chronic pain is still impacting your life and your function in a meaningful way that's restricting the things you want to do, then it it's totally appropriate, I think, to think about spinal cord stimulation. And importantly, I will add a huge predictor of final court stimulation success is psychological composition, you know, making sure the person doesn't have any untreated psychological illness and, and actually making sure their expectations going in are realistic. You're not going to cure anyone's pain. You may and that's, you know, a win, but it's very unlikely. And so, give folks the expectation that we hope to reduce your pain by 50% or we want you to list personally, I like functional goals where you say what is your pain preventing you from doing? We want to see if you can do X,Y, and Z during the trial period. Pharmacostimulation right now. Yeah. Biggest indication low back leg pain, Diabetic peripheral neuropathy. There is also an indication for CRPS, complex regional pain syndrome, a lesser, I'd say less common but also very debilitating pain condition. For better or worse. Tertiary quaternary care centers. You often will see spinal cord stem used off label for neuropathic type pain syndromes that are not explicitly better. That may be for examp…
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