The neuromodulation approach

Introduction

Neuromodulation means many things to many people—but essential to any point of view is that the term implies some type of intervention that interfaces on some level with the nervous system of the patient and modifies function with the goal of giving benefit to the patient. What remains important to the definition, however, is a deeper belief that this therapeutic approach itself has greater merit than any of the alternatives. This continues to be true for most areas of commercialized neuromodulation; in pain using spinal cord stimulation instead of medication or further surgery, in deep brain stimulation for movement disorders instead of medication and physical therapy, and in vagus nerve stimulation, deep brain stimulation, and responsive neural stimulation instead of further attempts to treat epilepsy with medication alone.

As a field of medicine reliant on the commercialized use of implanted devices, neuromodulation has continued to expand, likely reaching nearly 12 billion (USD) worldwide by 2022 (Allied Market Research, 2020). Annual growth has increased steadily over the past 5 years at 13%, previously 9%–10% prior to that, and has no obvious impediments to continuing to increase at these rates or more over the future decade as more devices, targets, and therapeutic platforms come online and previously immature economies are able to support the initial costs within their healthcare systems. Malaysia, for example, is expected to grow at a rate over 18% in neuromodulation through to 2022 at least. Several factors have continued to help support its growth: an aging population with longer term health burden from chronic disorders, longer and more difficult routes for neuropharmaceutical commercialization, and a persisting positive economic healthcare climate. Neuromodulation arguably stands today as one of the greatest sources of therapeutic intervention ever, in terms of numbers of people treated and overall contribution to quality of life.

Many types of practitioners and professionals have become involved in neuromodulation, from neurosurgeons and orthopedic surgeons, to pain physicians, physiatrists, and neurologists, to biomedical engineers and biophysicists. With nationalized funding and databases, industry growth and collaboration, and broad expansion in the number of patients treated with beneficial outcomes for what are typically intractable clinical problems, the general climate for neuromodulation remains favorable. Our goals herein are to impart both basic and not-so-basic aspects of neuromodulation to the reader—in terms of related basic science, design, application, revision and troubleshooting, the patient perspective, and the future. We focus primarily on electrical stimulation, with limited discussions of other modulation therapies when they may support an important principle overall. Readers will be exposed not only to thorough descriptions of every facet of neuromodulation by some of the most expert names currently in the field, but also to commentary from additional experts on the same topics, lending perspective and raising questions. Whether design engineer, graduate student, postdoctoral fellow, resident, neurologist, pain specialist, neurosurgeon, or other interested party to neuromodulation, our goal is to provide the ability to carry that responsibility into their future endeavors soundly.

Advances and new applications continue apace, but it would not be out of order to consider what has happened in neuromodulation and call it a “paradigm shift” [ ] in managing the clinical problems where it has been applied. This is a strong term, but emphasizes that, while previously the rampant belief has been that more and more precise pharmaceutical solutions could prevail for almost any clinical problem, the pharmaceutical approach has had holes punched in it. Neuromodulation has in the meantime pushed more and more therapy in the direction of so-called electro ceuticals, so much so that several of the largest pharmaceutical companies have created programs to develop and support “electroceutical” research. Certainly, the success of the pharmaceutical paradigm over previous methods of treatment has been profound and has created its own paradigm. But it has also been shown to have weakness and outright failures, in the form of side effects, tolerances, and inability to account for the anatomical precision necessary in some cases to bring about benefit. At the same time, surgical solutions without neuromodulation for many of the same problems—specifically, using resections or lesions—have soared with some successes, and plummeted with failure as well in cases where morbidity, imprecision, or irreversibility have left patients without benefit and possibly harmed further.

Kuhn pointed out that:

a student in the humanities has constantly before him a number of competing and incommensurable solutions to these problems, solutions that he must ultimately examine for himself” [ ], but science is different in that, once a paradigm shift has occurred, one would find it completely incompatible to posit that flies spontaneously generate from rotting meat, the sun revolves around the earth, or that the principles of Darwinian natural selection have not replaced Lamarck's.

Because of the successes in neuromodulation, practitioners must recognize that this same transition, this paradigm shift in the same way Kuhn notes above, is occurring, or has already occurred. As such, it would be, at this point, reprehensible not to consider deep brain stimulation, for example, in a child with DYT-1 positive dystonia, a dorsal column stimulator for refractory CRPS-I in an extremity, or motor cortex stimulation for poststroke facial or upper extremity pain. And these are but a few examples of how the neuromodulation approach has altered the algorithms of care. Neuromodulation has achieved this shift in every single field of application commercialized so far. One should not continue to ask: “What do I try when other traditional approaches have failed for this patient?,” one should now ask instead: “How can I use neuromodulation to help this patient?”—and this change to the neuromodulation approach makes all the difference.