Implantable cortical neural lead and method

A neural lead and method of treating neurological disorders by stimulation of the cerebral cortex of the brain is provided. The lead is designed for reduction of strain between the lead body and the lead paddle caused by the position of the lead body above the cranium and the lead paddle beneath the cranium. The lead is also designed to include a two dimensional chronic electrode array for better stimulation coverage of the target area of the cerebral cortex. A method of treating a neurological disorder by stimulating the cerebral cortex is also presented.

FIELD OF THE INVENTION

This invention relates generally to implantable chronic medical electrical leads and methods of use, and more particularly to an implantable neural lead for chronic stimulation of the cerebral cortex of the brain and method of use.

BACKGROUND OF THE INVENTION

Stimulation of the motor cortex is currently a promising therapy to treat deafferentation pain syndromes, including but not limited to central deafferentation pain arising from stroke, infection, trauma, spinal cord injury, multiple sclerosis, and peripheral pain syndromes including but not limited to trigeminal neuralgia, atypical facial pain, pain arising from peripheral nerve injury or disease including but not limited to nerve plexus avulsion, phantom limb pain, etc. Furthermore, stimulation of the motor cortex or other areas of the cerebral cortex of the brain are potentially promising therapies for treatment of other neurological disorders including, but not limited to movement disorders, neurodegenerative disorders, psychological disorders, and epilepsy, and other central and peripheral disorders.

To date, the best results of chronic motor cortex stimulation for pain have been obtained when stimulation was applied precisely to the zone of motor cortex corresponding to the part of the body in which the pain is experienced. It is therefore essential to respect the somatotopic organization of the motor cortex. The combination of imaging techniques including but not limited to Computerized Axial Tomography (CAT) scans, Magnetic Resonance Imaging (MRI), and three-dimensional neuronavigation procedures for anatomical localization and intraoperative anatomical and electrophysiological testing can greatly improve localization of the zone to be stimulated, thereby improving the clinical results. The objective is to ensure that at least one of the active electrodes is directly over the desired zone of stimulation.

The motor cortex is a narrow band of cortex situated in the precentral gyrus immediately anterior to the central sulcus. The Resume® lead (four electrodes arranged in linear fashion) manufactured by Medtronic, Inc., has been used for chronic stimulation of the motor cortex. If a Resume® lead is placed parallel to the central sulcus, several adjacent zones of the motor cortex can be stimulated simultaneously allowing the treatment of extensive pain, for example involving the entire hemibody. However, as the motor cortex is fairly narrow in the antero-posterior direction and follows the sometimes pronounced convolutions of the central sulcus, the electrode may be inadvertently placed anteriorly or posteriorly to the desired location. It is therefore preferred to place the Resume® lead perpendicularly to the central sulcus in order to ensure at least one of the four contacts of the electrode is directly over the motor cortex. The essential difficulty is to very precisely locate the “height” or mediolateral zone of representation of the part of the body affected by the pain. This localization requires the use of several modalities: imaging data and intra-operative somaesthetic evoked potentials (SEP), and clinical results (muscle contractions) of motor cortex stimulation. Even with these techniques, the limited coverage of this electrode makes it difficult to treat pain involving larger or more extensive regions of the body.

In addition, the method of localization and then implantation of the chronic Resume lead involved two major steps. First, the localization using the modalities mentioned above was performed including the use of a temporary grid of multiple electrodes such as those made by Ad-Tech Medical Instrument Corporation. Once the localization step is completed, the temporary grid electrodes are removed and replaced with a Resume® lead. (In some cases two Resume® leads have been implanted for chronic motor cortex stimulation.) This removal and replacement step adds a layer of complexity and risk of error to the surgical procedure because it requires very precise placement of the chronic lead following removal of the temporary multi-electrode grid used for localization. This step also increases potential short and long-term risks to the patient and extends procedure time. Moreover, financial expense is incurred by the need for both a temporary lead and a chronic or permanent lead.

The location of the paddle when stimulating the motor cortex or elsewhere on the cerebral cortex is beneath the cranium while the lead body is outside of, and must pass through, the cranium. This transition zone over the thickness of the cranium results in mechanical strain between the paddle and the lead body. This strain makes it more difficult to get and keep the entire lead paddle in contact with the tissue being stimulated, and creates risk to the integrity of the lead insulation and conductors.

BRIEF SUMMARY OF THE INVENTION

In a first embodiment, an implantable neural lead for use in electrically stimulating the cerebral cortex is provided. The neural lead includes a paddle, a lead body and a strain relief. The strain relief connects the paddle with the lead body and offsets the lead body from the paddle to accommodate the thickness of the patient's cranium.

In a second embodiment, an implantable neural lead for use in stimulating the cerebral cortex of the brain is provided. This embodiment lead includes a lead body and a paddle. The paddle has a two-dimensional electrode array with two sets of electrodes. The first set of electrodes of at least three is in a line defining an axis of the paddle. The second set of electrodes are offset in opposite directions from the axis of the paddle.

In a third embodiment, an implantable neural lead for use in electrically stimulating the cerebral cortex is provided. This embodiment neural lead includes a lead body and a lead paddle. The paddle includes a two-dimensional array of electrodes. The paddle lead also includes a peripheral edge that defines at least two peninsulas and at least two bays.

In a fourth embodiment, a method of treating a neurological disorder by electrical stimulation of the cerebral cortex is provided. The method includes providing an implantable neural lead, creating an opening through skull bone to access an area adjacent the cortex, placing the lead paddle within the area, determining a satisfactory orientation for the lead paddle, permanently attaching the lead paddle within the area for chronic stimulation, and implanting a pulse generator in electrical communication with the lead.

In a fifth embodiment, a method of treating a neurological disorder by electrical stimulation of the cerebral cortex is provided. This embodiment method includes providing an implantable neural lead, creating an opening in the skull bone to access an area adjacent the cortex, placing the lead paddle within the area, determining whether stimulation with the first set of electrodes provides sufficient relief, based on the previous step implanting either a single or a dual channel stimulator.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Referring toFIG. 1, an exemplary embodiment of an implantable neural lead of the present invention is shown. The neural lead100is adapted for electrically stimulating the brain. Neural lead100includes a paddle102, a plurality of electrodes104and a lead body106connected to the paddle by a strain relief108. The embodiment of neural lead100shown inFIG. 1includes a second lead body107and a second strain relief109for carrying a separate channel of conducting wires. Strain reliefs108and109are shown inFIG. 1with a partial cutaway. The neural lead100also includes suture holes110for attaching the neural lead100to the dura mater or other suitable tissue depending on the application.

Neural lead100may be used to treat any neurological disorder for which stimulation of the cortex of the brain has therapeutic value. Some example neurological disorders for use of the neural lead of this invention include, but are not limited to, treatment of pain such as facial, neck, limbic or other pain, movement disorders such as Parkinson's disease, essential tremor and dystonia, psychological disorders such as depression and obsessive compulsive disorder (OCD), epilepsy, Huntington's Disease, and neurodegenerative disorders. It is noted that pain is considered a neurological disorder for purposes of this application.

Neural lead100may be placed epidurally (outside the dura mater) or subdurally (beneath the dura mater). For example, in the case of treatment of pain the lead is likely to be used epidurally. In the case of epilepsy it is more likely that the lead would be used subdurally. In either case a craniotomy is performed and the paddle102placed beneath the cranium. In one application, lead100is placed epidurally adjacent the central sulcus of the cortex for stimulation to treat pain such as facial, neck or limbic pain.

Strain Relief

One of the novel features of the neural lead of the present invention is a strain relief. For purposes of this application, a strain relief is defined as a section of a lead that exists between a lead body or extension and a paddle and that displaces the lead body or extension some distance or offset from the paddle to accommodate generally the thickness of a patient's cranium. The strain relief allows the lead body or extension to lie above the cranium and the paddle to be situated beneath the cranium while reducing the amount of strain or pull between the paddle and the lead body or extension because of the displacement between the paddle and the lead body or extension.

One embodiment strain relief108is shown inFIGS. 1–3. Note that the discussion and description of strain relief108and lead body106also apply to strain relief109and lead body107. The strain relief108assists in reducing strain or pull between the paddle102and the lead body106. Strain relief108is flexible but is sufficiently resilient resulting in shape memory to maintain an offset between the plane of the paddle102and the lead body106. The purpose of the offset in the strain relief108is to allow a transition from the lead body106lying on top of the cranium120and the lead paddle102lying parallel to the lead body106but offset beneath the cranium120.

As shown inFIG. 2, strain relief108includes two maintained bends140and142. A maintained bend is bend in the strain relief that has shape memory so that if it is pressed on and deformed and then released it will return substantially to its original shape.

In the embodiment shown, the strain relief108is attached to the lead paddle102along the peripheral edge112of the paddle102. The distal ends111,113of the lead bodies106,107are attached to the strain reliefs108,109respectively.

As shown inFIG. 2, an exemplary angle between the plane of the paddle102and a line drawn through the middle of the strain relief108is 60 degrees. Preferably this angle is between 10 and 90 degrees. More preferably, this angle is between 30 and 80 degrees.

FIG. 1also shows the proximal end115of lead body106. The proximal contacts117are welded to the BSW wire that passes through the lead body106in electrical communication with the electrodes104. Epoxy is then backfilled to bond the stripped BSW wire to the inside of the proximal contacts117. A urethane strut124as described in U.S. Pat. No. 5,935,159 owned by Medtronic, Inc. may be used to prevent kinking of the lead bodies106,107.

FIG. 2is a cross sectional view of the lead100including one embodiment interaction of the lead100with the patient's cranium120and dura mater122.FIG. 2shows the cross section after a craniotomy has been performed. In this embodiment ofFIG. 2, the paddle102is placed epidurally with electrodes104in contact with the dura mater.

As shown inFIG. 2, the paddle102includes a first major surface114and a second opposite major surface116with a fibrous reinforcing layer118sandwiched between. The fibrous reinforcing layer helps resist stretching of the paddle102. This additional stiffness may or may not be desired depending on the application of the lead. One embodiment of the fibrous reinforcing layer118is a Dacron® reinforcing mesh. The electrodes104extend through windows in the first major surface114to allow contact with the tissue to be stimulated.

Preferably, the strain reliefs108,109offset the lead bodies106,107from the first major surface114by a distance of between about 4 mm and 10 mm. More preferably, the offset is about 6 mm.

A rongeur may be used to make notches (not shown) in either the bone flap or the cranium to accommodate the strain reliefs108,109when there is misalignment between the craniotomy and the stimulation site. The gap between the strain reliefs108,109and the notches will eventually fill with new bone isolating all but the portion of each strain relief that lies on the cranium from any flexing due to lead body movement. The physician will position the notches such that they direct the strain reliefs108and109and the lead bodies106and107toward the location of the eventual tunnel for the extension. In an alternative embodiment, the strain reliefs or lead bodies may also be anchored or sutured outside the cranium for further reduction of flexing.

FIG. 3provides a cutaway view of strain relief108to show one embodiment assembly technique. This technique involves the use of a urethane adhesive to attach two slit urethane tubes130and132to the urethane lead body106. This assembly is inserted into the cavity134provided in the molded silicone rubber strain relief108. Then the cavity134is filled with silicone adhesive to bond to the strain relief108. When the adhesive has cured, it provides a mechanical lock around the tubes130and132on the lead body106.

The definition of a strain relief can include a strain relief connector. A strain relief connector is defined as a strain relief that includes a connector. The connector could be a female or male or any other type of connector for connecting a paddle to an extension.FIG. 7shows a perspective view of a lead200that includes one embodiment strain relief connector202having a male connector206. Connector206connects to a female connector on an extension. This embodiment lead also has 8 electrodes204.

It is noted that the strain relief of this invention could be used with any type of paddle lead including one or two-dimensional paddle leads. A one-dimensional paddle lead is defined for this application as being a paddle lead that has a plurality of electrodes in a line and no electrodes out of alignment with the line. A two-dimensional paddle lead is defined for this application as being a paddle lead with three or more electrodes positioned in such a way that they are not all in a line. A two-dimensional paddle lead includes a lead with a line of electrodes and one electrode out of alignment with the line. For purposes of this application, a two-dimensional paddle lead also includes non-planar orientation of electrodes.

An alternate embodiment lead of the present invention could include only a single lead body and single strain relief. In such an embodiment, all of the conducting wires would pass through the single lead body and strain relief instead of being separated as shown inFIG. 1. Furthermore, more than two lead bodies and more than two strain reliefs could be utilized.

Electrode Configuration

The number of electrodes104as well as the position of the electrodes104on the paddle102may vary greatly within the scope of the present invention. In one particularly advantageous embodiment, the lead paddle102has a two dimensionally distributed electrode array including a plurality of electrically isolated electrodes, the plurality of electrodes including a first set of at least three electrodes defining an axis of the paddle and a second set of electrodes offset in opposite directions from the axis of the paddle. For example, the first set of electrodes inFIG. 5is marked as electrodes0,1,2, and3defining an axis of the paddle102. The second set of electrodes is electrodes4,5,6, and7with electrodes4and5offset from the axis of the paddle102in an opposite direction from electrodes6and7respectively. Other embodiments having more or fewer electrodes are considered. For example, the first set of electrodes could be only three electrodes in a line and forming an axis of the paddle with a fourth electrode offset on one side of the axis of the paddle and a fifth electrode offset on the other side of the axis of the paddle (embodiment not shown but considerFIG. 5but without electrodes3,5, and7).

The lead shown inFIG. 1has 8 electrodes104. This distribution of electrodes allows stimulation parallel to the central sulcus while ensuring stimulation of the motor cortex. The electrode configuration shown onFIG. 1allows for the certainty of stimulating parallel to the central sulcus and ensuring stimulation of the motor cortex.

FIGS. 9 and 10illustrate two exemplary orientations or placements of the lead100relative to the central sulcus450. As can be seen and envisioned there are many possible placements of the lead100relative to the central sulcus or other fissure of the cortex. The exact placement desired will depend on the results of the navigational and other screening and positioning techniques performed.

The neural lead of this invention may be used with any pulse generator.FIG. 4shows a pulse generator150implanted pectorally and connected to an extension160that is connected to a lead100(not shown inFIG. 4). In a preferred embodiment, the lead100,200or300is used with a Synergy® or Soletra® implantable pulse generator (IPG) made by Medtronic, Inc. The Synergy® IPG is capable of dual channel stimulation so that each set of electrodes is a separate channel. The Synergy® stimulator is also capable of stimulating across channels which is helpful in some cases of motor cortex stimulation.

In the embodiment shown inFIG. 5, the conductive wires from electrodes0,1,2, and3are carried through strain relief109and lead body107. The wires from electrodes4,5,6, and7are carried through strain relief108and lead body106. In this way each lead body and hence each set of electrodes can be connected to a separate channel of a dual channel stimulator.

Paddle Dimensions

In a preferred embodiment, the diameter and thickness of the paddle are 1.575 inches and 0.054 inches, respectively. Other preferred dimensions are shown inFIG. 6that shows the lead paddle102from the side opposite the exposed electrodes104(the side facing toward the cranium facing away from the brain).FIG. 6also shows one way of assigning numbers to the electrodes. The lead100may be marked with these numbers for use by the physician. Of course the electrodes could be numbered or otherwise marked in any number of ways.

Paddle Shape

The shape of the paddle may be round as shown inFIGS. 1,5,6, and7or it may be other shapes. Because craniotomies are typically round, one preferred embodiment is the round shape. However, an alternative preferred embodiment is shown inFIG. 8. This “flower” design paddle lead300allows the craniotomy size to be smaller and allow for the paddle to be more easily slid under the cranium around the edges of the craniotomy. The lead300includes paddle302, electrodes304, and strain reliefs308and309. The paddle302includes a peripheral edge defining six peninsulas307and six bays306, wherein the peninsulas307can be easily slid under the cranium. Reference numerals310and312show the location of suture of the dura to the cranium and suture of the lead to the dura respectively.

Method of Treating a Neurological Disorder

Due to the distribution of the electrodes104, the lead100,200or300can also be used for intraoperative detection, as these 8 electrode leads can be used to record somaesthetic evoked potentials, which confirm the position of the central sulcus. Similarly, this same electrode can be used to stimulate the cortex intraoperatively in order to confirm the position of the various functional zones of the motor cortex. This technique should therefore represent a major financial economy, since a fairly costly disposable electrode with several contacts previously had to be used for electrophysiological detection, while the Resume® lead was used for chronic stimulation. Also the use of the lead of this invention for both localization and chronic stages eliminates a layer of complexity to the surgical operation reduces potential for placement error, reduces short and long-term risks to the patient, reduces procedure time, and makes the procedure more economical

An exemplary embodiment method of treating a neurological disorder is shown inFIG. 11. As indicated by block500, localization of the target zone of the cortex is performed by imaging techniques including but not limited to Computerized Axial Tomography (CAT) scans, Magnetic Resonance Imaging (MRI), and three-dimensional imaging with a neuronavigation systems and procedures.

As indicated by block502, a circular craniotomy, 4 to 5 cm in diameter, is performed with the guidance of the neuronavigation system. The 8-electrode paddle is placed on the dura mater and connected to a somaesthetic evoked potential (SEP) recording apparatus as shown in blocks504and506.

The position of the lead over the central sulcus is confirmed by correlating the anatomical detection data (neuronavigation) with the SEP data obtained after stimulation of the median nerve at the wrist as shown in block508.

As shown in block510, the position of the various functional zones of the motor cortex can be confirmed by stimulating the electrodes supposedly situated directly over the motor cortex and observing the response. For example, in order to treat facial pain, the zone of motor cortex for which stimulation induces muscle contractions of the face is identified.

As indicated in block512, the lead is then attached to the dura mater by several sutures. Other attachment methods may be used such as anchors or other methods known in the art.

When anatomical and electrophysiological data are concordant and very clear, the two leads of the electrode are connected during the same operation to an IPG.

Depending on the results of the above trials and screening, the next step shown as block514involves a determination of whether a single channel IPG such as a Soletra® stimulator or a dual channel stimulator such as a Synergy® stimulator is preferred. If use of electrodes0,1,2, and3are sufficient to alleviate pain or otherwise reduce symptoms of the disorder, then a single channel stimulator is sufficient. If use of the other electrodes4,5,6, or7provides further reduction in symptoms, then a dual channel stimulator may be preferred.

As indicated in block516, the selected stimulator is then implanted in electrical communication with the electrodes104.

When there is a doubt about efficacy based on location or other factors, due to a discrepancy between anatomical and electrophysiological data, the leads may be exteriorized and a clinical test performed during the days following the operation. A single channel or dual channel stimulator may then be implanted depending on the clinically effective electrodes.

Thus, embodiments of the implantable cortical neural lead and method are disclosed. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.