Subcutaneous Stimulation: How to Assess Optimal Implantation Depth , Paul Verrills, MD

Transcription

Neuromodulation: Technology at the Neural Interface
Received: September 22, 2010
Revised: December 24, 2010
Accepted: February 19, 2011
(onlinelibrary.wiley.com) DOI: 10.1111/j.1525-1403.2011.00357.x
Subcutaneous Stimulation: How to Assess
Optimal Implantation Depth
ner_357
343..348
David Abejón, MD*, Timothy Deer, MD†, Paul Verrills, MD‡
Introduction: Subcutaneous stimulation (peripheral nerve field stimulation) is a novel neuromodulation modality that has
increased in its utilization during the last 10 years. It consists of introducing a lead in the subdermal level to stimulate the small
nerve fibers in that layer. Unlike other neuromodulation techniques including direct peripheral nerve stimulation, spinal cord
stimulation, or deep brain stimulation, the precise target is not identified.
Materials and Methods: To date, there is no clear guideline on the appropriate depth or a method to achieve reproducibility of
the appropriate depth to place these leads. From clinical experience, we have found that when electrodes are placed in a layer that
is too superficial, stimulation is often painful or lacks efficacy. Further, if they are too deep, the patient may not feel adequate
paresthesia or get uncomfortable stimulation including, in some circumstances, muscle contractions.
Results: In this small series, we demonstrate a novel concept using a radiofrequency stimulation probe to identify the appropriate
depth to place the lead. Reproducibility of results will add clarity to the accumulating data and hopefully increase the chances of
adequate stimulation coverage and pain relief.
Keywords: Chronic pain, electrode placement, implant, implantation, technical report
Conflicts of Interest: Dr. David Abejón is a speaker for St. Jude Medical, Medtronic, and Boston Scientific. Dr. Timothy Deer is a
consultant for Azur, Bioness, Medtronic, Spinal Modulation, St. Jude, Stryker, and Vertos. Dr. Paul Verrills reported no conflicts of
interest.
INTRODUCTION
Subcutaneous stimulation, also called peripheral nerve field
stimulation or peripheral subcutaneous field stimulation (1), is a
relatively new neurostimulation modality. The first articles date from
2004, and since then, publications on this subject have grown
exponentially.
Studies have been carried out on the implantation of stimulation
leads in the lumbar area, to manage low-back pain secondary to
failed back surgery syndrome (2). The use of these systems has
recently been utilized in situations in which it would be difficult to
achieve paresthesia coverage with spinal cord stimulation systems
(3) or in cases where epidural lead implantation is too complicated or
risky (4–6). The number of publications and posters has increased
exponentially since 2004, but some reasonable doubts about the
development of this modality still linger. These doubts have arisen
because of the lack of a prospective randomized study on the procedure and because of confusion regarding the indications for this
technique. There also are unresolved issues in the area of the science
of subcutaneous stimulation, including the mechanism of action,
adequate lead depth of implant, and the most adequate parameters
and stimulation modalities. This paper will provide an overview of
indications, and then examine the proper depth of lead implantation
in order to achieve activation of the subcutaneous nerve fibers.
INTRODUCTION TO THE SURGICAL TECHNIQUE
www.neuromodulationjournal.com
Address corresponding to: David Abejón, MD, Hospital Universitario Puerta de
Hierro Majadahonda, Madrid—Pain Unit, C/ Joaquin Rodrigo, 2.28222, Majadahonda, Madrid, Spain. Email: [email protected]
* Hospital Universitario Puerta de Hierro Majadahonda, Madrid—Pain Unit,
Madrid, Spain;
†
Center for Pain Relief, Charleston, WV, USA; and
‡
Metro Spinal Clinic—Research, South Caulfield, Vic., Australia
For more information on author guidelines, an explanation of our peer review
process, and conflict of interest informed consent policies, please go to http://
www.wiley.com/bw/submit.asp?ref=1094-7159&site=1
© 2011 International Neuromodulation Society
Neuromodulation 2011; 14: 343–348
343
In order to stimulate the subcutaneous nervous system we must
implant one or more leads into the subdermic layer of the skin. The
depth of this implant has not been reported in the literature to date,
and this can be problematic in achieving an optimal outcome. Leads
that are implanted in the more superficial tissues such as the dermis
can result in painful stimulation often described as “burning” and
stabbing. Leads that are implanted in the deeper tissue layers can
result in the inability to perceive stimulation or in muscle recruitment and uncomfortable stimulation. In both of these scenarios, the
outcome will not be acceptable. It is important for the clinician to
achieve the proper depth of stimulation, which is a conundrum
based on current publications.
Imaging techniques can be helpful in locating specific nerve
fibers in both the upper and lower extremity (7–9). This type of
guidance could be critical in subcutaneous stimulation and could
result in the difference between a good outcome and a failure to
achieve relief.
To address these issues and in order to achieve proper depth for
stimulation, the following technique has been developed in Spain.
ABEJÓN ET AL.
Figure 1. Marking of the implant area and location of the patient’s maximum
pain spot. The photograph shows a bilateral pain, and the introduction point
and target are marked on the left painful spot.
344
A needle is used to deliver current from a radiofrequency generator
in the stimulation function to identify target fibers. This targeting
also can be achieved by using a peripheral nerve stimulator in a
manner used for peripheral nerve blocks, for regional anesthesia.
After informed consent, the patient is taken to the operating
theatre and prepped and draped in the proper fashion. The target
area for stimulation is marked using a permanent marker before
entering the operation room (Fig. 1). If the patient suffers from
allodynia, the lead placement may have to be adapted to the
areas just outside of the zone of allodynia. This may require lead
cross-talk between two separate leads to achieve pain reduction
(Fig. 2). The patients also are given intravenous antibiotics prior to
incision.
The needle is guided to the proper pain target of maximum discomfort by x-ray guidance and landmarks. Once the needle is in
place we proceed to stimulate with the radiofrequency generator.
This device allows for 2 Hz motor stimulation and 50 Hz sensory
stimulation. The devices used are a RFG-3C Plus generator (Radionics, Burlington, MA, USA) and a 60-mm CXE cannula with a
4-mm active tip. Sensory stimulation is performed until a paresthesia is elicited in the painful area (Fig. 3), the goal is to achieve
paresthesia at 0.5 v although it is accepted with the range of 0.5 to
1 v. The needle-generator connection is protected with a sterile
tube cover to guarantee sterility. The proper depth of stimulation
is located based on stimulation, and this depth is confirmed by
lateral fluoroscopic guidance to identify the needle tip. Keeping
the cannula in position, and with a continuous vision of fluoroscopy in lateral view, so that the display of the depth of radiofrequency cannula is appropriate, we introduce a Tuohy needle or a
14G angiocatheter through which the lead will be advanced and
placed at the depth of sensory stimulation (Fig. 4). As in other
stimulation modalities, a stimulation test is performed after positioning the lead, until the paresthesia perceived by the patient
coincides with his/her painful area and this paresthesia is pleasant
and comfortable.
Figure 2. Delimitation of the allodynic area, around which electrodes are
implanted. Each line represents the introduction of one lead.
Figure 3. Introduction of a 6-mm CXE needle with 4-mm active tip, used for
sensitive stimulation and location of the implant depth.
We use trial lead during the test phase that will be removed
afterwards. Surgical technique in the test phase only consists of
locating the stimulation depth and introducing the lead through a
Tuohy needle or 14G angiocatheter, as explained; no incision is
made on the skin. Leads are introduced through the needle and
fixed directly to the skin with Steri-Strip (Fig. 5). Test duration may
vary from 1 to 2 weeks. Following a positive trial we allow 2–4
weeks before performing the permanent implant. This waiting
period is recommended to allow for skin healing to reduce the risk
of infection (Fig. 6).
During the permanent implantation we perform a 3–4 cm long
incision to anchor the leads to the fascia, as in stimulation of the
epidural space, and the leads are tunneled to the generator pocket.
In some cases, especially with leads placed in the upper buttock or
SUBCUTANEOUS DEPTH
Figure 4. The lead is introduced and located at the depth where an adequate
paresthesia was achieved with the RF needle.
just above the beltline, IPG pocket can be used to introduce and
anchor the leads, in order to avoid additional incisions.
The use of widely spaced four contact or normal spaced eight
contact leads depends on the area needed for paresthesia to
achieve the stimulation goal, the complexity of the system based on
other stimulation targets. Regardless of the system chosen, the
most important outcome is to achieve adequate stimulation in the
most painful area with an appropriate depth of lead placement.
The experience to date with 21 leads in 10 patients has shown that
the average target zone is at 10.5 mm (9.8–11.3 mm) below the
surface of the skin (Tables 1 and 2).
INDICATIONS
Indications are not well established because therapeutic modalities
have sometimes been confusing (2,10–13). One of the greatest confounding points is the use of the terms for stimulating a peripheral
nerve directly and the fibers of a nerve as interchangeable. Taxonomy remains confusing, but the targets are very different. For
example, in a recent publication a novel device was introduced to
stimulate the median nerve. In that setting the depth is determined
by a peripheral nerve stimulator to determine lead delivery (14). This
is a different issue than we are addressing in this publication, which
is to discuss a new method of determining proper depth of stimulation when targeting nerve fibers of a larger defined nerve.
In our opinion, the main indications for the use of this therapy can
by summarized in two specific items:
• Hard-to-stimulate areas with other stimulation modalities
• Well-defined areas of pain
From this standpoint, this therapy can be proposed for patients
with axial pain, from cervical to lumbar, which is hard to manage
with spinal cord stimulation (15,16). Other hard-to-stimulate zones
are the paravertebral and the scapular areas, and groin regions
where spinal cord stimulation usually does not provide a consistent
and constant paresthesia. Another indication that looks adequate is
the management of painful scars with nerve entrapment (17), as it is
often a well-delineated area. The physician can adapt these devices
to treat other areas of concern and the identification of new targets
are being evaluated in clinical studies. (18,19).
DISCUSSION
management and can be performed with low risks and minimal
insult during a trialing phase (6,20,21).
The main problems that are faced when attempting a new therapeutic modality are common to all techniques: overuse, lack of randomized, prospective, and double-blinded studies, poor patient
selection, adverse events, and lack of long-term cost-effectiveness
data. In addition to those dilemmas, in this arena we are faced with
some critical questions:
•
•
•
•
•
The mechanism of action
The optimal surgical technique
Proper indications and patient selection groups
The optimal stimulation parameters and modes
The long-term efficacy and cost-effectiveness
Although we don’t have substantial replies to any of these issues or
problems addressed above, based on the current knowledge in the
field we can make some comment:
The mechanism of action of spinal cord stimulation has been
defined by the work of Linderoth, Foreman, and Meyerson (22,23).
Direct stimulation of the peripheral nerve has been theorized to act
by creating a change in nerve transmission or a balance of A delta
and C fiber response compared with other nocioreceptors. Stimulation of the nerve fibers of the subcutaneous tissue has been theorized to act by changing the mechanism of tissue activation at the
site of the pain generator and the responding nerve tissue. PNFS
may theoretically operate in one of the following mechanisms:
impact local blood flow, block cell membrane depolarization,
change neurotransmitter levels, and change the message at the
spinal cord level. Investigators are debating the mechanisms, but
many think PNFS may change the levels of localized and systemic
endogenous endorphins, thereby impacting the nociceptive
threshold in the target zone. More basic research is needed in this
area.
Surgical technique and precise indications seem to be another
obstacle for the development of this therapy. The surgical technique
is relatively straightforward and has been described in the different
articles referenced in this work. The concept idea of being able to
stimulate before introduction of the leads is appealing and is pro-
345
Peripheral subcutaneous stimulation is the newest area of neuromodulation that is providing an exciting new frontier in pain
Figure 5. Trial phase: leads are not anchored to the patient’s skin. Some SteriStrip bands are enough to keep leads in place, don’t harm the area for the final
implantation, and don’t cause discomfort for the patient.
ABEJÓN ET AL.
Figure 6. Permanent implant.
Table 1. Patients’ Demographic Data.
Name
Diagnosis
Leads
Manufacturer
IPG
Depth (cm)
AGM
MGC
JSM
JSB
CDV
FA
MLH
LJF
RAM
SC
Abdominal pain
FBSS
Abdominal pain
FBSS
Abdominal pain
FBSS
FBSS
FBSS
Cervicalgia
FBSS
1 ¥ 8 sc
2 ¥ 4 sc (2 ¥ 4 epidural)
4 ¥ 4 sc
2 ¥ 8 sc
2 ¥ 8 sc
2 ¥ 8 sc
Medtronic
ANS
Boston
Boston
Medtronic
ANS
Medtronic
ANS
ANS
ANS
Restore ultra
Eon mini
Precision
Precision
Restore ultra
Eon mini
Restore ultra
Eon mini
Eon mini
Eon mini
11.3
10.5
9.9
10.4
10.5
10.6
9.8
11.0
10.7
10.3
FBSS, failed back surgery syndrome; SC, subcutaneous.
Table 2. Patients’ Stimulation Parameters.
Name
pT
Main T
Discomfort T
Fq (Hz)
Pw (ms)
Impedance (W)
AGM
MGC
JSM
JSB
CDV
FA
MLH
LJF
RAM
SC
1.5
3.6
2.0
10.5
3.5
8.0
3.0
6.0
2.5
5.5
2.0
4.2
2.4
11.0
4.5
9.0
3.5
9.0
3.5
6.5
10.5
4.8
2.8
12.8
10.5
13.0
10.0
12.0
4.5
8.0
60
70
40
50
60
60
60
50
50
50
330
300
300
300
390
300
300
200
287
300
533
687
1186
518
404
398
927
902
502
545
Fq, frequency; pT, perception threshold; Pw, pulse width; T, threshold.
346
posed as a reproducible way to assess the best implantation depth
to obtain the most comfortable paresthesia.
The use of imaging techniques alone does not currently solve this
problem as it only indicates the radiological landmark in which the
Touhy needle is residing at the time of lead deployment.
To know the exact depth, it would possibly be necessary to devise
some kind of mathematical model as the one developed by Manola
and Holsheimer for spinal cord or cortex stimulation (24,25), which
would help us to know what is really stimulated and what we should
do to improve results (26).
In our opinion, the best option to know the most precise
positioning of the electrodes in this kind of stimulation
would be a combination of stimulation (to locate the targeted
area) and echography (to define the exact depth of the
electrodes).
One of the doubts related to the therapy will be overcome if we
can establish the depth to place the lead(s) exactly. The combination of these two techniques, together with the development of a
suitable model, will strongly help the programing and stimulating
techniques (27).
Once we have an exact definition of how to perform the technique, which are the best indications and parameters, multicenter
and randomized studies will be easy to perform in order to provide
further scientific validation of the technique.
SUBCUTANEOUS DEPTH
CONCLUSIONS
Here we provide for the first time a reproducible technique to establish ideal depth of stimulation in the subcutaneous area of patients
suffering complex, difficult pain, and who have failed conservative
management, and whose pain regions would not normally be treatable with spinal cord stimulation (28,29).
Authorship Statements
Dr. Abejón conceived the idea and prepared the manuscript draft.
Dr. Deer provided important intellectual input on the mechanisms
of action of peripheral nerve field stimulation and edited the manuscript for English. Dr. Verrills provided important intellectual input
on peripheral nerve field stimulation and edited the manuscript for
English. All authors approved the final version of the manuscript.
How to Cite this Article:
Abejón D., Deer T., Verrills P. 2011. Subcutaneous Stimulation: How to Assess Optimal Implantation Depth.
REFERENCES
COMMENTS
In "Subcutaneous Stimulation: How to Assess Optimal Implantation
Depth," Abejon et al. provide a concise technical introduction to a
novel intra-operative mapping technique for the placement of peripheral nerve field stimulation (PNfS) percutaneous electrodes. Previous
reports have discussed the use of ultrasound to determine depth of
implantation, but as the authors point out, there is some ambiguity in
the literature regarding PNfS as distinct from classical peripheral nerve
stimulation (PNS) in which a specific named nerve is directly targeted.
Ultrasound has generally been investigated primarily for PNS applications where direct visualization of the target nerve clarifies the desired
implant depth. In PNfS, no such discrete target structure exists, and the
functional nature of the target increases the uncertainty regarding
optimal implant depth. The technique for subcutaneous electrode
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applied the principles of electrophysiologic mapping of pain generators with RF stimulation to the subcutaneous space to identify the
optimum implant depth, and then used lateral fluoroscopy to maintain
this depth along the implant trajectory. They report their results in a
small series of patients. This is certain to be a useful technique for the
many implanters who are using PNfS in cases that are difficult to obtain
paresthesia coverage with more traditional techniques.
Kenneth M. Alo’, M.D.
Clinical Member
The Methodist Hospital Research Institute
The Texas Medical Center
Houston, TX, USA
Director, Section of Neuro-Cardiology
Associate Professor, Institute of Cardiology and Vascular Medicine
Monterrey Technical University, Monterrey Mexico
(Instituto de Cardiologia y Medicina Vascular del TEC de Monterrey)
Erich O. Richter, M.D.
Assistant Professor of Neurosurgery
Department of Neurosurgery
LSU Health Sciences Center, New Orleans
New Orleans, LA, USA
347
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ABEJÓN ET AL.
***
The field of peripheral subcutaneous stimulation (or peripheral field
stimulation) is rapidly growing and is gaining a very important role in
the management of intractable pain with neurostimulation techniques. Even though the technique seems to be simple, proper positioning of the leads can prove to be tricky. As the authors appropriately
point out, there is no objective instrumental method to judge the
exact depth of the electrode placement. Personal clinical experience
has allowed the reviewer to successfully place subcutaneous leads in
most circumstances without any additional tools. The technique
described by the authors, however, can be useful in less experienced
implanters and certainly could avoid repetitive leads passes before
finding the proper depth.
***
The authors have reported a novel technique to stimulate subcutaneous neural targets and ascertain the appropriate depth of these targets
for optimal stimulation outcomes. Only further study will ultimately
decide the merits of this approach. Currently, inaccuracies in our
understanding of subcutaneous stimulation include uncertainty
regarding the mechanisms of effect and a lack of uniformity in implantation techniques. Imaging of soft tissues or other localization techniques such as the described use of electrical verification of target
depth via radiofrequency hardware may aid the field in achieving
better standardization. The authors accurately point out the ongoing
need for more basic research in the use of subcutaneous stimulation,
to better understand exactly how this new and exciting technique
works.
Giancarlo Barolat, M.D.
INS Founder & Director at Large
Medical Director, Barolat Neuroscience
Denver, CO, USA
Marc Huntoon, M.D.
Professor of Anesthesiology
Consultant in Anesthesiology, Pain Medicine
College of Medicine
Mayo Clinic
Rochester, MN, USA
Comments not included in the Early View version of this paper.
348

Subcutaneous Stimulation: How to Assess Optimal Implantation Depth , Paul Verrills, MD

Transcription

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