Neurostimulation for Pain: Earlier May Be Better
Neurostimulation is clinically effective and cost efficient, but it's not being used appropriately in many patients with chronic pain, according to experts in the field who are addressing current gaps related to this treatment modality.
Part of the problem, according to Simon Thomson, MBBS, president, International Neuromodulation Society, and lead consultant, Pain Management Centre, Basildon and Thurrock University Hospital, Essex, United Kingdom, is that some practitioners "tend to have a rather conservative idea about how these patients should be treated and they tend to over vex about any potential complications."
The result, he told Medscape Medical News, is that "some people are just left to lead their lives with intolerably disabling pain and it doesn't have to be like that."
The INS convened 60 neurostimulation experts from around the world to evaluate the current literature and to form expert opinion on appropriate use of neurostimulation in chronic pain. The researchers identified deficiencies in evidence related to their use and to address these gaps, they initiated a discussion on related issues which appears in 4 new articles.
The papers were published in the August 2014 issue of Neuromodulation.
Clear Deficiencies
These papers broach the topics of the appropriate use of neurostimulation of the spinal cord and peripheral nervous system and of the intracranial and extracranial space and head, avoiding and treating related complications, as well as new and evolving neurostimulation therapies.
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Dr. Simon Thomson |
Implantable technologies include traditional dorsal column stimulation or spinal cord stimulation (SCS), peripheral nerve stimulation (PNS), peripheral nerve field stimulation, deep brain stimulation (DBS), and motor cortex stimulation. Stimulation systems typically have 3 parts: electrical leads, an impulse generator, and a patient controller.
Researchers initially searched EMBASE, MEDLINE, the Cochrane database, peer-reviewed nonindexed journals, and materials presented at national and international meetings to identify guideline statements for use of neurostimulation therapies to treat chronic neuropathic pain.
They identified 22 guideline statements, including 13 that were society sponsored, 2 from research foundations, 2 that were government supported, and 1 published as a position statement.
The researchers noted "clear deficiencies" in scope of coverage or evidence synthesis and lack of transparency of funding. "Unfortunately, guidelines are often polarized in favor of, or in opposition to, the reviewed topic, based by the authors' specialty and political affiliations," the authors, led by Timothy R. Deer MD, Center for Pain Relief, Charleston, West Virginia, write.
The reviewers also noted that none of the current guidelines or consensus statements attempts to digest and comment on all currently available modalities of neuromodulation.
Appropriate Use
In the new paper on appropriate use of neurostimulation of the spinal cord and peripheral nervous system, the committee determined that the therapy can be life-changing for many patients.
Members concluded that appropriate neurostimulation is safe and effective in some chronic pain conditions and that technological refinements and clinical evidence will continue to expand its use.
Since its introduction in 1967, SCS has become a well-accepted treatment for chronic pain, the authors noted. It targets the dorsal column of the spinal cord for the relief of pain of neuropathic origin.
Electrical stimulation of the spinal cord is approved by the FDA for chronic painful disorders of the trunk and extremities, such as failed back surgery syndrome, complex regional pain syndrome, and radiculopathy, but it has been used for other neuropathic syndromes, such as traumatic neuropathies,diabetic neuropathy, and postherpetic neuralgia.
According to the authors, evidence for the mechanism of action for electrical stimulation of the spinal cord is "elusive" and "somewhat conflicting."
Recent developments in technology have led to the introduction of a new and potentially advantageous target for SCS — the dorsal root ganglion — which could expand the number of patients with chronic pain who might be candidates for neurostimulation and improve outcomes.
For disorders of the head and neck, the committee said that when possible, extracranial stimulation should be "an earlier option in the treatment algorithm."
"Over time with improved devices and targets, the ability to reduce medications and to improve outcomes will likely be enhanced," they write.
Deep Brain Stimulation
Committee members determined that while intracranial neurostimulation has the potential to help many patients, DBS is limited by its inherent invasiveness and risks.
Although it's a treatment option for movement disorders such as Parkinson's disease or essential tremor, some psychiatric disorders, and possibly Alzheimer's disease in the future, "we should continue to find targets outside the cranium when treating pain, if at all possible," they write.
"We want to always make sure that we do the least invasive but effective treatment," added Dr. Thomson. Aside from using DBS for certain painful conditions, including facial pain due to damaged trigeminal nerves, DBS may not be the best treatment for pain and has not been tested for this in randomized clinical trials, he said.
PNS has proven to be a successful approach to treating migraine and other headache disorders and facial pain despite using devices that are "not ideal or made for the head and neck," said the authors.
Again, the committee recommended that PNS of the extracranial nerves (eg, the occipital nerve) be used earlier in pain treatment, before initiation of long-term, long-acting opioid pain management.
"There is good evidence and proof that this [extracranial stimulation] is helpful in chronic migraine," said Dr. Thomson. "We want to see it positioned firmly within treatment algorithms."
On the other hand, while many patients aren't given the option of neurostimulation until well into their disease management, "we don't want people with a few headaches who have not been tried on a triptan or another simple therapy to be implanted" with a stimulation device to control pain, said Dr. Thomson.
"We are trying to describe thresholds of when this treatment should be made available," he added.
The role of headache specialists is to diagnose the type of headache, make sure the patient is prescribed a series of pharmacologic agents, and if that fails (which occurs in some patients), to make sure that extracranial neurostimulation is available, he added.
"Occipital nerve stimulation is the best treatment for migraine that is refractory to regular treatment and is severe and disabling, so we use this when people's lives are intolerable."
Complications
In the paper on complications, the reviewers said that SCS and PNS can result in a range of hardware-related adverse effects, in many cases involving the lead.
"Lead breakage and lead migration would be the Achilles heel of spinal cord stimulation," said Dr. Thomson. "But a lot of effort has gone into improving the durability of the leads, and improving anchors which usually grip the lead and keep it in place."
Biological complications can include infection, and serious adverse effects can include neurologic damage. "The one we are all worried about is epidural hematoma causing neurological harm," said Dr. Thomson, adding that this is "very, very rare."
Although rare, such complications are more common if the practitioner or surgeon is inexperienced. It does happen, though, that practitioners with very little training do SCS or PNS procedures.
"These are the people who basically bring the technique into disrepute," said Dr. Thomson. "That's why we are trying to talk about standards of training."
The expert panel recommended that implanters have hospital-admission privileges, perform at least 10 supervised implantations during training, monitor their outcomes and quality indicators, and perform a high volume of implant procedures to keep their skills up-to-date.
They would also like to see all permanent implants be performed in a full medical facility rather than an office or clinic setting unless it meets the same sterile-environment standards as an accredited hospital or surgery center.
Exciting Work
In the paper on new and evolving therapies, the reviewers cited some "exciting" work coming down the pipeline. One development gaining attention is an external stimulator that can be passed over the vagal nerve, said Dr. Thomson.
"A patient picks up their device like an iPhone, puts it under the chin or neck and can stimulate the nerve, or they might wear a wraparound ear piece" and stimulate the vagal nerve near the ear drum.
Implantable devices are likely to become smaller, too. "There's 1 new device which is essentially just a lead where all the electronics are within it," said Dr. Thomson.
In addition to smaller components, including tinier batteries, new technologies may include nerve response feedback capabilities and improved materials. Dr. Thomson foresees ceramic replacing titanium to house the implantable pulse generators, a move that would make recharging the device less cumbersome.
Reviewers said they feel the need to focus not only on improving products in relation to safety, simplicity, and costs but also to focus on impacting disease states. They said that they're "encouraged" by the possible use of stimulation to correct abnormal function of the immune system.
On the issue of cost, Dr. Thomson said the evidence shows that when compared to usual care (eg, drugs, counseling, physiotherapy), neurostimulation may require more of an initial investment but over time, proves to be "strongly cost effective."
Although the reviewers suggested that future studies choose a "comparator" based on "usual care," they recognized that this can differ; for example, the comparator is repeat back surgery for failed back surgery syndrome in North America but not in some European countries.
"There is often a poor consensus on choice of comparator with marked variation from one health-care system to another," they note.
Good-quality clinical science in this field is moving quickly — and finally getting funded — and Dr. Thomson sees this as "incredibly important" step. "The historical lack of clinical rigor and clinical studies has held this field back," he said.
As the field of neurostimulation is changing so rapidly, the research team plans to revisit these issues every 2 years, said Dr. Thomson.
Dr. Thomson reports he consults for Axonics, for British Standards of Industry, and for Boston Scientific. Dr. Deer reports that he holds minor stock options in Bioness Inc, Spinal Modulation Inc, and Nevro Corp. He is a paid consultant for St. Jude Medical Inc, Spinal Modulation Inc, Bioness Inc, Nevro Corp, and Medtronic Inc. He has patent relationships with Bioness Inc and Nevro Corp. He is an advisor for St. Jude Medical Inc, Medtronic Inc, Spinal Modulation Inc, Bioness Inc, Nevro Corp, Flowonix Medical Inc, and Jazz Pharmaceuticals PLC.