U.S. patent application number 13/753326 was filed with the patent office on 2013-06-06 for pain management with stimulation subthreshold to paresthesia.
The applicant listed for this patent is Eyad KISHAWI, Jeffery M. KRAMER. Invention is credited to Eyad KISHAWI, Jeffery M. KRAMER.
Application Number | 20130144359 13/753326 |
Document ID | / |
Family ID | 42781839 |
Filed Date | 2013-06-06 |
United States Patent
Application |
20130144359 |
Kind Code |
A1 |
KISHAWI; Eyad ; et
al. |
June 6, 2013 |
PAIN MANAGEMENT WITH STIMULATION SUBTHRESHOLD TO PARESTHESIA
Abstract
Devices, systems and methods are provided for treating pain
while minimizing or eliminating possible complications and
undesired side effects, particularly the sensation of paresthesia.
This is achieved by stimulating in proximity to a dorsal root
ganglion with stimulation energy in a manner that will affect pain
sensations without generating substantial sensations of
paresthesia. In some embodiments, such neurostimulation takes
advantage of anatomical features and functions particular to the
dorsal root ganglion.
Inventors: |
KISHAWI; Eyad; (San Carlos,
CA) ; KRAMER; Jeffery M.; (San Francisco,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KISHAWI; Eyad
KRAMER; Jeffery M. |
San Carlos
San Francisco |
CA
CA |
US
US |
|
|
Family ID: |
42781839 |
Appl. No.: |
13/753326 |
Filed: |
January 29, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12730908 |
Mar 24, 2010 |
8380318 |
|
|
13753326 |
|
|
|
|
61163007 |
Mar 24, 2009 |
|
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Current U.S.
Class: |
607/46 |
Current CPC
Class: |
A61N 1/36017 20130101;
A61N 1/36021 20130101; A61N 1/0551 20130101; A61N 1/36071 20130101;
A61N 1/36157 20130101 |
Class at
Publication: |
607/46 |
International
Class: |
A61N 1/36 20060101
A61N001/36 |
Claims
1. A method of treating pain in a patient comprising: positioning a
lead having at least one electrode disposed thereon so that at
least one of the at least one electrode is in proximity to a dorsal
root ganglion; and providing stimulation energy to the at least one
of the at least one electrode so as to stimulate at least a portion
of the dorsal root ganglion, wherein together the positioning of
the lead step and the providing stimulation energy step affect pain
sensations without generating substantial sensations of
paresthesia.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/730,908, entitled "PAIN MANAGEMENT WITH
STIMULATION SUBTHRESHOLD TO PARESTHESIA," filed Mar. 24, 2010, now
Publication No. US-2010-0249875-A1, which claims priority under 35
U.S.C. 119(e) to U.S. Provisional Patent Application No.
61/163,007, entitled "PAIN MANAGEMENT WITH SUBTHRESHOLD
STIMULATION," filed Mar. 24, 2009, which is incorporated herein by
reference.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0002] NOT APPLICABLE
REFERENCE TO A "SEQUENCE LISTING," A TABLE, OR A COMPUTER PROGRAM
LISTING APPENDIX SUBMITTED ON A COMPACT DISK
[0003] NOT APPLICABLE
BACKGROUND
[0004] For more than 30 years, spinal cord stimulation (SCS) has
been used to treat a variety of pain syndromes. The goal of SCS is
to create paresthesia that completely and consistently covers the
painful areas, yet does not cause uncomfortable sensations in other
areas. Paresthesia may be defined as a sensation of tingling,
pricking, or numbness in an area of the body. It is more generally
known as the feeling of "pins and needles". In some instances, the
feeling of paresthesia is preferred over the feeling of pain. In
SCS, paresthesia production is accomplished by stimulating A.beta.
fibers in the dorsal column and/or the dorsal roots. Dorsal column
stimulation typically causes paresthesia in several dermatomes at
and below the level of the stimulator. In contrast, dorsal root
stimulation activates fibers in a limited number of rootlets in
close proximity to the stimulator and causes paresthesia in only a
few dermatomes. Because of these factors, dorsal root stimulation
with an SCS stimulator may not produce sufficient pain relief. In
addition, stimulation of the roots with an SCS stimulator can cause
uncomfortable sensations and motor responses. These side effects
may occur at pulse amplitudes that are below the value needed for
full paresthesia coverage. Therefore, the clinical goal of SCS is
to produce an electrical field that stimulates the relevant spinal
cord structures without stimulating the nearby nerve root.
[0005] Intraspinal nerve root stimulation is a technique related to
SCS, except that electrodes are placed along the nerve rootlets in
the lateral aspect of the spinal canal (this area is known as "the
gutter"), rather than over the midline of the spinal cord. The
electrodes are mounted on a cylindrical lead rather than on a
traditional SCS paddle lead. The accuracy of the leads' placement
within the gutter is confirmed by stimulating the nerve roots at
perceptible levels, which result in paresthesia in the local area.
Sensory paresthesia may be generated by stimulating at a level
above the threshold for sensory recruitment. This may be used in
conjunction with SCS to treat certain pain conditions.
[0006] For some patients, paresthesia is an undesired effect and is
not a well tolerated alternative to pain. Therefore, improved
treatments are needed to provide pain relief with minimal undesired
effects. At least some of these objectives will be met by the
present invention.
SUMMARY OF THE DISCLOSURE
[0007] The present invention provides devices, systems and methods
for treating conditions, such as pain, while minimizing or
eliminating possible complications and undesired side effects. In
particular, the devices, systems and methods treat pain without
generating substantial sensations of paresthesia. This is achieved
by stimulating in proximity to a dorsal root ganglion with specific
stimulation energy levels, as will be described in more detail
herein.
[0008] In a first aspect of the present invention, a method is
provided of treating pain in a patient comprising positioning a
lead having at least one electrode disposed thereon so that at
least one of the at least one electrode is in proximity to a dorsal
root ganglion, and providing stimulation energy to the at least one
of the at least one electrode so as to stimulate at least a portion
of the dorsal root ganglion. Together the positioning of the lead
step and the providing stimulation energy step affect pain
sensations without generating substantial sensations of
paresthesia.
[0009] In some embodiments, providing stimulation energy comprises
providing stimulation energy at a level below a threshold for
A.beta. fiber recruitment. And, in some embodiments, providing
stimulation energy comprises providing stimulation energy at a
level below a threshold for A.beta. fiber cell body
recruitment.
[0010] In other embodiments, providing stimulation energy
comprises: a) providing stimulation energy at a level above a
threshold for A.delta. fiber cell body recruitment, b) providing
stimulation energy at a level above a threshold for C fiber cell
body recruitment, c) providing stimulation energy at a level above
a threshold for small myelenated fiber cell body recruitment, or d)
providing stimulation energy at a level above a threshold for
unmyelenated fiber cell body recruitment.
[0011] In still other embodiments, providing stimulation energy
comprises providing stimulation energy at a level which is capable
of modulating glial cell function within the dorsal root ganglion.
For example, in some embodiments, providing stimulation energy
comprises providing stimulation energy at a level which is capable
of modulating satellite cell function within the dorsal root
ganglion. In other embodiments, providing stimulation energy
comprises providing stimulation energy at a level which is capable
of modulating Schwann cell function within the dorsal root
ganglion.
[0012] In yet other embodiments, providing stimulation energy
comprises providing stimulation energy at a level which is capable
of causing at least one blood vessel associated with the dorsal
root ganglion to release an agent or send a cell signal which
affects a neuron or glial cell within the dorsal root ganglion.
[0013] In some embodiments, positioning the lead comprises
advancing the lead through an epidural space so that at least a
portion of the lead extends along a nerve root sleeve angulation.
And, in some instances advancing the lead through the epidural
space comprises advancing the lead in an antegrade direction.
[0014] In a second aspect of the present invention, a method is
provided for treating a patient comprising selectively stimulating
a small fiber cell body within a dorsal root ganglion of the
patient while excluding an A.beta. fiber cell body with the dorsal
root ganglion of the patient. In some embodiments, the small fiber
body comprises an A.delta. fiber cell body. In other embodiments,
the small fiber body comprises a C fiber cell body.
[0015] In a third aspect of the present invention, a method is
provided for treating a patient comprising identifying a dorsal
root ganglion associated with a sensation of pain by the patient,
and neuromodulating at least one glial cell within the dorsal root
ganglion so as to reduce the sensation of pain by the patient. In
some embodiments, the at least one glial cell comprises a satellite
cell. In other embodiments, the at least one glial cell comprises a
Schwann cell. And, in some embodiments, neuromodulating comprises
providing stimulation at a level that reduces the sensation of pain
without generating substantial sensations of paresthesia.
[0016] In a fourth aspect of the present invention, a method is
provided for treating a patient comprising positioning a lead
having at least one electrode disposed thereon so that at least one
of the at least one electrode is in proximity to a dorsal root
ganglion, and providing stimulation energy to the at least one
electrode so as to stimulate at least one blood vessel associated
with the dorsal root ganglion in a manner that causes the at least
one blood vessel to release an agent which neuromodulates a neuron
within the dorsal root ganglion. In some embodiments, the agent
comprises a neuromodulatory chemical that affects the function of
neurons involved in pain sensory transduction.
[0017] In a fifth aspect of the present invention, a system is
provided for treating pain in a patient comprising a lead having at
least one electrode disposed thereon, wherein the lead is
configured for placement in proximity to a dorsal root ganglion,
and a pulse generator configured to provide stimulation energy to
the at least one of the at least one electrode while the lead is
positioned in proximity to the dorsal root ganglion so as to
stimulate at least a portion of the dorsal root ganglion in a
manner which affects pain sensations without generating substantial
sensations of paresthesia.
[0018] In some embodiments, the pulse generator provides
stimulation energy at a level at below a threshold for A.beta.
fiber recruitment. In other embodiments, the pulse generator
provides stimulation energy at a level below a threshold for
A.beta. fiber cell body recruitment. In other embodiments, the
pulse generator provides stimulation energy at a level above a
threshold for A.delta. fiber cell body recruitment. In still other
embodiments, the pulse generator provides stimulation energy at a
level above a threshold for C fiber cell body recruitment. In some
embodiments, the pulse generator provides stimulation energy at a
level above a threshold for small myelenated fiber cell body
recruitment. And, in some embodiments, the pulse generator provides
stimulation energy at a level above a threshold for unmyelenated
fiber cell body recruitment.
[0019] In some embodiments, the pulse generator provides
stimulation energy at a level which is capable of modulating glial
cell function within the dorsal root ganglion. For example, in some
embodiments, the pulse generator provides stimulation energy at a
level which is capable of modulating satellite cell function within
the dorsal root ganglion. In other embodiments, the pulse generator
provides stimulation energy at a level which is capable of
modulating Schwann cell function within the dorsal root
ganglion.
[0020] In some instances, the pulse generator provides stimulation
energy at a level which is capable of causing at least one blood
vessel associated with the dorsal root ganglion to release an agent
or send a cell signal which affects a neuron or glial cell within
the dorsal root ganglion.
[0021] And, in some embodiments, the lead is configured to be
advanced in an antegrade direction through an epidural space and
positioned so that at least a portion of the lead extends along a
nerve root sleeve angulation.
[0022] Other objects and advantages of the present invention will
become apparent from the detailed description to follow, together
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1A provides a schematic illustration of a spinal cord,
associated nerve roots and a peripheral nerve on a spinal level and
FIG. 1B illustrates cells within a DRG.
[0024] FIGS. 2A-2C provide a cross-sectional histological
illustration of a spinal cord and a DRG under varying levels of
magnification.
[0025] FIG. 3 illustrates an embodiment of a lead, having at least
one electrode thereon, advanced through the patient anatomy so that
at least one of the electrodes is positioned on a target DRG.
[0026] FIG. 4 provides a schematic illustration of the lead
positioned on a DRG.
[0027] FIG. 5 illustrates a graph showing an example relationship
between threshold stimulus and nerve fiber diameter.
[0028] FIG. 6 illustrates recruitment order based on nerve fiber
diameter.
[0029] FIG. 7 illustrates recruitment order based on cell body
size.
[0030] FIG. 8 illustrates recruitment order differences based on
location of stimulation.
[0031] FIG. 9 provides a schematic illustration of an embodiment of
the lead positioned on a DRG, including various cells and
anatomical structures associated with the DRG.
[0032] FIGS. 10A-10D, 11, 12 illustrate embodiments of a lead and
delivery system.
DETAILED DESCRIPTION
[0033] The present invention provides devices, systems and methods
for treating pain while minimizing or eliminating possible
complications and undesired side effects, particularly the
sensation of paresthesia. This is achieved by stimulating in
proximity to a dorsal root ganglion with stimulation energy in a
manner that will affect pain sensations without generating
substantial sensations of paresthesia. In some embodiments, such
neurostimulation takes advantage of anatomical features and
functions particular to the dorsal root ganglion, as will be
described in more detail below. The devices, systems and methods
are minimally invasive, therefore reducing possible complications
resulting from the implantation procedure, and targeted so as to
manage pain sensations with minimal or no perceptions such as
paresthesia.
[0034] FIG. 1A provides a schematic illustration of a spinal cord
S, associated nerve roots and a peripheral nerve on a spinal level.
Here, the nerve roots include a dorsal root DR and a ventral root
VR that join together at the peripheral nerve PN. The dorsal root
DR includes a dorsal root ganglion DRG, as shown. The DRG is
comprised of a variety of cells, including large neurons, small
neurons and non-neuronal cells. Each neuron in the DRG is comprised
of a bipolar or quasi-unipolar cell having a soma (the bulbous end
of the neuron which contains the cell nucleus) and two axons. The
word soma is Greek, meaning "body"; the soma of a neuron is often
called the "cell body". Somas are gathered within the DRG, rather
than the dorsal root, and the associated axons extend therefrom
into the dorsal root and toward the peripheral nervous system. FIG.
1B provides an expanded illustration of cells located in the DRG,
including a small soma SM, a large soma SM' and non-neuronal cells
(in this instance, satellite cells SC). FIGS. 2A-2C provide a
cross-sectional histological illustration of a spinal cord S and
associated nerve roots, including a DRG. FIG. 2A illustrates the
anatomy under 40.times. magnification and indicates the size
relationship of the DRG to the surrounding anatomy. FIG. 2B
illustrates the anatomy of FIG. 2A under 100.times. magnification.
Here, the differing structure of the DRG is becoming visible. FIG.
2C illustrates the anatomy of FIG. 2A under 400.times.
magnification focusing on the DRG. As shown, the larger soma SM'
and the smaller somas SM are located within the DRG.
[0035] In some embodiments, stimulation of a DRG according to the
present invention is achieved with the use of a lead having at
least one electrode thereon. The lead is advanced through the
patient anatomy so that the at least one electrode is positioned
on, near, about or in proximity to the target DRG. The lead and
electrode(s) are sized and configured so that the electrode(s) are
able to minimize or exclude undesired stimulation of other
anatomies.
[0036] FIG. 3 illustrates an embodiment of a lead 100, having at
least one electrode 102 thereon, advanced through the patient
anatomy so that at least one of the electrodes 102 is positioned on
a target DRG. In this example, the lead 100 is inserted epidurally
and advanced in an antegrade direction along the spinal cord S. As
shown, each DRG is disposed along a dorsal root DR and typically
resides at least partially between the pedicles PD or within a
foramen. Each dorsal root DR exits the spinal cord S at an angle
.theta.. This angle .theta. is considered the nerve root sleeve
angulation and varies slightly by patient and by location along the
spinal column. However, the average nerve root angulation is
significantly less than 90 degrees and typically less than 45
degrees. Therefore, advancement of the lead 100 toward the target
DRG in this manner involves making a sharp turn along the angle
.theta.. A turn of this severity is achieved with the use of
delivery tools and design features specific to such lead placement
which will be described in more detail in later sections. In
addition, the spatial relationship between the nerve roots, DRGs
and surrounding structures are significantly influenced by
degenerative changes, particularly in the lumbar spine. Thus,
patients may have nerve root angulations which differ from the
normal anatomy, such as having even smaller angulations
necessitating even tighter turns. The delivery tools and devices
accommodate these anatomies.
[0037] FIG. 4 provides a schematic illustration of an embodiment of
the lead 100 positioned on a DRG. As illustrated, the DRG includes
smaller somas SM and larger somas SM'. Each soma is connected with
an associated axon or nerve fiber which extends through the root.
The axon or nerve fiber is a long, slender projection of a nerve
cell, or neuron that conducts electrical impulses away from the
neuron's cell body or soma. The smaller somas SM have smaller axons
AX and the larger somas SM' have larger axons AX'. Typically, axons
or nerve fibers are recruited electrically according to size.
Referring to FIG. 5, a graph is provided which illustrates an
example relationship between threshold stimulus and nerve fiber
diameter. Generally, as the nerve fiber diameter increases, the
threshold stimulus decreases. Thus, as illustrated in FIG. 6,
larger mylenated fibers (A.beta. fibers) are recruited before
smaller mylenated fibers (A.delta. fibers), which are in turn
recruited before small unmylenated fibers (C fibers).
[0038] Referring to FIG. 7, the opposite is true of cell bodies
compared to nerve fibers. Generally, it takes less current to
recruit or modulate a smaller cell body or soma membrane than a
larger one. Thus, as shown in FIG. 8, when low stimulation is
provided in region A (to the cell bodies SM', SM) the smaller
diameter cell bodies SM are selectively stimulated before the
larger diameter cell bodies SM'. This is due to the relatively
smaller charge it takes to effectively modulate membrane function
of a smaller cell body. However, when low stimulation is provided
in region B (to the axons AX', AX) the larger axons AX' are
stimulated before the smaller axons AX. Referring back to FIG. 4,
since the cell bodies or somas are located within the DRG, region A
generally corresponds to the DRG and region B generally corresponds
to the dorsal root DR.
[0039] When a patient experiences pain, the nociceptive or painful
stimuli are transduced from peripheral structures to the central
nervous systems through small diameter, thinly myelinated and
unmyelinated afferent nerve fibers or axons AX. Electrically, these
fibers are more difficult to selectively target since larger
diameter fibers or axons AX' are preferentially activated by
electrical currents based upon the above described size principle.
These larger fibers AX' are associated with sensory stimuli such as
light touch, pressure and vibration and well as paresthesia such as
generated by SCS.
[0040] The present invention provides methods and devices for
preferentially neuromodulating the smaller diameter axon/smaller
soma neurons over the larger diameter axon/larger soma neurons.
This in turn interrupts pain transmission while minimizing or
eliminating paresthesia. Referring again to FIG. 4, an example is
illustrated of a lead 100 positioned so that at least one of the
electrodes 102 is disposed so as to selectively stimulate the DRG
while minimizing or excluding undesired stimulation of other
anatomies, such as portions of the dorsal root DR. This allows the
smaller diameter axon/smaller soma neurons to be recruited before
the larger diameter axon/larger soma neurons. Consequently, these
neurons involved in pain transduction can be modulated without
producing paresthesias. This is achieved with the use of less
current or lower power stimulation, i.e. stimulation at a
subthreshold level to paresthesia. The effect of this preferential,
targeted neuromodulation is analgesia without resultant
paresthesias. In addition, lower power stimulation means lower
power consumption and longer battery life.
[0041] Conventional spinal stimulation systems typically provide
stimulation with a frequency of about 30-120 Hz. In contrast,
therapeutic benefits have been achieved with the devices and
methods described herein at stimulation frequencies below those
used in conventional stimulation systems. In one aspect, the
stimulation frequency used for the DRG stimulation methods
described herein is less than 25 Hz. In other aspects, the
stimulation frequency could be even lower such as in the range of
less than 15 Hz. In still other aspects, the stimulation frequency
is below 10 Hz. In one specific embodiment, the stimulation
frequency is 5 Hz. In another specific, embodiment, the stimulation
frequency is 2 Hz. In addition to lower stimulation frequencies,
other stimulation patterns for the inventive devices and methods
are also lower than those used in conventional stimulation systems.
For example, embodiments of the present invention have achieved
repeatable dermatome specific pain relief using a stimulation
signal having an amplitude of less than 500 microamps, a pulse
width of less than 120 microseconds and a low stimulation frequency
as discussed above. It is believed that embodiments of the present
invention can achieve dermatome specific pain relief using signals
having pulse widths selected within the range of 60 microseconds to
120 microseconds. It is believed that embodiments of the present
invention can achieve dermatome specific pain relief using a signal
having an amplitude of about 200 microamps. In one specific
example, repeatable dermatome specific pain relief was achieved in
an adult female using a signal with an amplitude of 200 microamps,
a pulse width of 60 microseconds and a frequency of 2 Hz. It may
also be appreciated that other suitable stimulation signal
parameters may be used along, such as provided in U.S. patent
application Ser. No. 12/607,009 entitled "SELECTIVE STIMULATION
SYSTEMS AND SIGNAL PARAMETERS FOR MEDICAL CONDITIONS," filed Oct.
27, 2009, now Publication No. US-2010-0137938-A1, incorporated
herein by reference for all purposes.
[0042] In addition to neuronal cells, non-neuronal cells, such as
glial cells, are located within the DRG. Glial cells surround
neurons, hold them in place, provide nutrients, help maintain
homeostasis, provide electrical insulation, destroy pathogens,
regulate neuronal repair and the removal dead neurons, and
participate in signal transmission in the nervous system. In
addition, glial cells help in guiding the construction of the
nervous system and control the chemical and ionic environment of
the neurons. Glial cells also play a role in the development and
maintenance of dysfunction in chronic pain conditions. A variety of
specific types of glial cells are found within the DRG, such as
satellite cells and Schwann cells.
[0043] Satellite cells surround neuron cell bodies within the DRG.
They supply nutrients to the surrounding neurons and also have some
structural function. Satellite cells also act as protective,
cushioning cells. In addition, satellite cells can form gap
junctions with neurons in the DRG. As opposed to classical chemical
transmission in the nervous system, gap junctions between cells
provide a direct electrical coupling. This, in turn, can produce a
form of a quasi glial-neuronal syncytium. Pathophysiologic
conditions can change the relationship between glia and cell bodies
such that the neurons transducting information about pain can
become dysfunctional. Therefore neurostimulation of the DRG can not
only directly affect neurons but also impact the function of glial
cells. Modulation of glial cell function with neurostimulation can
in turn alter neuronal functioning. Such modulation can occur at
levels below a threshold for generating sensations of
paresthesia.
[0044] FIG. 9 provides a schematic illustration of an embodiment of
the lead 100 positioned on a DRG. As illustrated, the DRG includes
satellite cells SC surrounding smaller somas SM and larger somas
SM'. In some embodiments, stimulation energy provided by at least
one of the electrodes 102 neuromodulates satellite cells SC. Such
neuromodulation impacts their function and, secondarily, impacts
the function of associated neurons so as to interrupt or alter
processing of sensory information, such as pain. Consequently, DRG
satellite cell neuromodulation can be a treatment for chronic
pain.
[0045] Another type of glial cells are Schwann cells. Also referred
to as neurolemnocytes, Schwann cells assist in neuronal survival.
In myelinated axons, Schwann cells form the myelin sheath. The
vertebrate nervous system relies on the myelin sheath for
insulation and as a method of decreasing membrane capacitance in
the axon. The arrangement of the Schwann cells allows for saltatory
conduction which greatly increases speed of conduction and saves
energy. Non-myelinating Schwann cells are involved in maintenance
of axons. Schwann cells also provide axon support, trophic actions
and other support activities to neurons within the DRG.
[0046] Referring again to FIG. 9, Schwann cells SWC are illustrated
along the axons of a neuron within the DRG. In some embodiments,
stimulation energy provided by at least one of the electrodes 102
of the lead 100 neuromodulates Schwann cells SWC. Such
neuromodulation impacts their function and, secondarily, impacts
the function of associated neurons. Neuromodulation of Schwann
cells impacts neuronal processing, transduction and transfer of
sensory information including pain. Thus, DRG stimulation relieves
pain in the short and long term by impacting function of Schwann
cells. This also may be achieved at stimulation levels below a
threshold for generating sensations of paresthesia.
[0047] Beyond the neural cells (neurons, glia, etc) that are
present in the DRG, there is a rich network of blood vessels that
travel in and about the DRG to encapsulate the DRG and provide a
blood supply and oxygen to this highly metabolically active neural
structure. FIG. 9 schematically illustrates a blood vessel BV
associated with and an example DRG. In some embodiments,
stimulation energy is provided by at least one of the electrodes
102 of the lead 100. Stimulation of the DRG can cause the release
of a variety of agents from the neurons, glia and/or blood vessels
which ultimately impact the function of neurons involved in the
transduction and processing of sensory information, including pain.
For example, in some embodiments stimulation of the DRG causes one
or more types of neurons and/or one or more types of glial cells to
release vasoactive agents which affect at least one blood vessel.
The at least one blood vessel in turn releases neuronal agents
impact the function of neurons in processing pain. Or, the at least
one blood vessel releases glial active agents which indirectly
impacts the function of neurons in processing pain. In other
embodiments, stimulation of the DRG directly affects the associated
blood vessels which provide vessel to neuron cell signaling or
vessel to glial cell signaling. Such cell signaling ultimately
impacts neuronal function, such as by altering metabolic rate or
inducing the release of neural responsive chemicals which, in turn,
directly change the cell function. The change in cell function
induces analgesia or pain relief in the short-term, mid-term and
long-term. Such changes may occur at stimulation levels below a
threshold for generating sensations of paresthesia.
[0048] Desired positioning of a lead 100 near the target anatomy,
such as the DRG, may be achieved with a variety of delivery
systems, devices and methods. Referring back to FIG. 3, an example
of such positioning is illustrated. In this example, the lead 100
is inserted epidurally and advanced in an antegrade direction along
the spinal cord S. As shown, each DRG is disposed along a dorsal
root DR and typically resides at least partially between the
pedicles PD or within a foramen. Each dorsal root DR exits the
spinal cord S at an angle .theta.. This angle .theta. is considered
the nerve root sleeve angulation and varies slightly by patient and
by location along the spinal column. However, the average nerve
root angulation is significantly less than 90 degrees and typically
less than 45 degrees. Therefore, advancement of the lead 100 toward
the target DRG in this manner involves making a sharp turn along
the angle .theta.. In addition, the spatial relationship between
the nerve roots, DRGs and surrounding structures are significantly
influenced by degenerative changes, particularly in the lumbar
spine. Thus, patients may have nerve root angulations which differ
from the normal anatomy, such as having even smaller angulations
necessitating even tighter turns. Turns of this severity are
achieved with the use of delivery tools having design features
specific to such lead placement.
[0049] Referring to FIGS. 10A-10D, an example lead and delivery
devices for accessing a target DRG are illustrated. FIG. 10A
illustrates an embodiment of a lead 100 comprising a shaft 103
having a distal end 101 with four electrodes 102 disposed thereon.
It may be appreciated that any number of electrodes 102 may be
present, including one, two, three, four, five, six, seven, eight
or more. In this embodiment, the distal end 101 has a closed-end
distal tip 106. The distal tip 106 may have a variety of shapes
including a rounded shape, such as a ball shape (shown) or tear
drop shape, and a cone shape, to name a few. These shapes provide
an atraumatic tip for the lead 100 as well as serving other
purposes. The lead 100 also includes a stylet lumen 104 which
extends toward the closed-end distal tip 106. A delivery system 120
is also illustrated, including a sheath 122 (FIG. 10B), stylet 124
(FIG. 10C) and introducing needle 126 (FIG. 10D).
[0050] Referring to FIG. 10B, an embodiment of a sheath 122 is
illustrated. In this embodiment, the sheath 122 has a distal end
128 which is pre-curved to have an angle .alpha., wherein the angle
.alpha. is in the range of approximately 80 to 165 degrees. The
sheath 122 is sized and configured to be advanced over the shaft
103 of the lead 100 until a portion of its distal end 128 abuts the
distal tip 106 of the lead 100, as illustrated in FIG. 11. Thus,
the ball shaped tip 106 of this embodiment also prevents the sheath
122 from extending thereover. Passage of the sheath 122 over the
lead 100 causes the lead 100 to bend in accordance with the
precurvature of the sheath 122. Thus, the sheath 122 assists in
steering the lead 100 along the spinal column S and toward a target
DRG, such as in a lateral direction.
[0051] Referring back to FIG. 10C, an embodiment of a stylet 124 is
illustrated. The stylet 124 has a distal end 130 which is
pre-curved so that its radius of curvature is in the range of
approximately 0.1 to 0.5. The stylet 124 is sized and configured to
be advanced within the stylet lumen 104 of the lead 100. Typically
the stylet 124 extends therethrough so that its distal end 130
aligns with the distal end 101 of the lead 100. Passage of the
stylet 124 through the lead 100 causes the lead 100 to bend in
accordance with the precurvature of the stylet 124. Typically, the
stylet 124 has a smaller radius of curvature, or a tighter bend,
than the sheath 122. Therefore, as shown in FIG. 12, when the
stylet 124 is disposed within the lead 100, extension of the lead
100 and stylet 124 through the sheath 122 bends or directs the lead
100 through a first curvature 123. Further extension of the lead
100 and stylet 124 beyond the distal end 128 of the sheath 122
allows the lead 100 to bend further along a second curvature 125.
This allows the laterally directed lead 100 to now curve around
toward the target DRG along the nerve root angulation. This two
step curvature allows the lead 100 to be successfully positioned so
that at least one of the electrodes 102 is on, near or about the
target DRG, particularly by making a sharp turn along the angle
.theta..
[0052] Thus, the lead 100 does not require stiff or torqueable
construction since the lead 100 is not torqued or steered by
itself. The lead 100 is positioned with the use of the sheath 122
and stylet 124 which direct the lead 100 through the two step
curvature. This eliminates the need for the operator to torque the
lead 100 and optionally the sheath 122 with multiple hands. This
also allows the lead 100 to have a lower profile as well as a very
soft and flexible construction. This, in turn, minimizes erosion
and discomfort created by pressure on nerve tissue, such as the
target DRG and/or the nerve root, once the lead 100 is implanted.
For example, such a soft and flexible lead 100 will minimize the
amount of force translated to the lead 100 by body movement (e.g.
flexion, extension, torsion).
[0053] Referring back to FIG. 10D, an embodiment of an introducing
needle 126 is illustrated. The introducing needle 126 is used to
access the epidural space of the spinal cord S. The needle 126 has
a hollow shaft 127 and typically has a very slightly curved distal
end 132. The shaft 127 is sized to allow passage of the lead 100,
sheath 122 and stylet 124 therethrough. In some embodiments, the
needle 126 is 14 gauge which is consistent with the size of
epidural needles used to place conventional percutaneous leads
within the epidural space. However, it may be appreciated that
other sized needles may also be used, particularly smaller needles
such as 16-18 gauge. Likewise, it may be appreciated that needles
having various tips known to practitioners or custom tips designed
for specific applications may also be used. The needle 126 also
typically includes a Luer-Lok.TM. fitting 134 or other fitting near
its proximal end. The Luer-Lok.TM. fitting 134 is a female fitting
having a tabbed hub which engages threads in a sleeve on a male
fitting, such as a syringe.
[0054] Methods of approaching a target DRG using such a delivery
system 120 is further described and illustrated in U.S. Patent
Application No. 61/144,690 filed Jan. 14, 2009, incorporated herein
by reference for all purposes, along with examples of other
delivery systems, devices and methods applicable to use with the
present invention.
[0055] It may be appreciated that other types of leads and
corresponding delivery systems may be used to position such leads
in desired orientations to provide stimulation subthreshold to
paresthesia. For example, the lead may have a pre-curved shape
wherein the lead is deliverable through a sheath having a
straighter shape, such as a substantially straight shape or a
curved shape which is has a larger radius of curvature than the
lead. Advancement of the lead out of the sheath allows the lead to
recoil toward its pre-curved shape. Various combinations of
curvature between the lead and sheath may allow for a variety of
primary and secondary curvatures. Once the lead is desirably
placed, the sheath may then be removed.
[0056] It may also be appreciated that a variety of approaches to
the DRG may be used, such as an antegrade epidural approach, a
retrograde epidural approach, a transforamenal approach or an
extraforaminal approach (approaching along a peripheral nerve from
outside of the spinal column), and a contralateral approach, to
name a few. Likewise, the at least one electrode may be positioned
in, on or about, in proximity to, near or in the vicinity of the
DRG.
[0057] Although the foregoing invention has been described in some
detail by way of illustration and example, for purposes of clarity
of understanding, it will be obvious that various alternatives,
modifications, and equivalents may be used and the above
description should not be taken as limiting in scope of the
invention which is defined by the appended claims.
INCORPORATION BY REFERENCE
[0058] All publications and patent applications mentioned in this
specification are herein incorporated by reference to the same
extent as if each individual publication or patent application was
specifically and individually indicated to be incorporated by
reference.
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