Surgery – Diagnostic testing – Structure of body-contacting electrode or electrode inserted...
Reexamination Certificate
1999-09-30
2002-01-29
Dvorak, Linda C. M. (Department: 3739)
Surgery
Diagnostic testing
Structure of body-contacting electrode or electrode inserted...
C607S116000, C607S140000, C606S129000
Reexamination Certificate
active
06343226
ABSTRACT:
The invention relates to the electrical stimulation of neural tissue in order to abolish the symptoms of nervous system and neuromuscular disorders.
So far electrical treatment with deep brain stimulation (DBS) has primarily been used to treat symptoms of Parkinson's disease which is a disorder affecting the nerve cells in the brain stem. These cells contain the nerve-transmitter dopamine. The disabling symptoms of the disease are tremor, muscular rigidity and dyskinesia which can be treated with a DBS electrode when traditional medical treatment fails. The neurostimulation blocks the symptoms of the disease resulting in increased quality of life for the patient. Besides this aim, one major benefit of this treatment is that the symptoms are reversible.
The electrode presently used consists of a tip with four platinum conductors and connecting wire coils embedded in silicone. The electrode is placed in the nervous tissue by a stereotaxic operation whereby the electrode tip is placed in the desired target with an accuracy of 0.5 mm. To determine the stereotaxic coordinates of the desired target, a stereotaxic frame is fixed onto the patient's head. The frame functions as an external Cartesian coordinate system with X, Y and Z axes. The next step is a computerized tomography (CT) scan or magnetic resonance imaging (MRI) resulting in CT or MR images displaying the brain anatomy and the external stereotaxic frame. From these images, the appropriate coordinate set of any brain region can now be determined. Briefly explained, the following surgery consists of a burr hole made in the patient's scull under local anesthesia. A mandrin consisting of a thin stainless steel tube, fixed onto the stereotaxic frame with a blunt tipped stilette inside is gently introduced into the brain of the patient. The tip of the mandrin is placed just above the desired target (approximately 5 mm) whereupon the stilette is removed and the quadripolar electrode is introduced through the steel tube. The electrode which is highly flexible is kept rigid by a thin inner tungsten stilette. With the electrode just above the target area, test stimulation is performed and a neurologist is simultaneously assessing the stimulation effect on the parkinsonian symptoms of the awake patient. If no effect is determined the electrode is advanced stepwise towards the target area with test stimulation and neurological assessment at each step. When the level of maximal stimulation effect is determined, the electrode is left in situ and the tungsten stilette is removed. The patient is now placed under general anesthesia and the electrode is connected through an extra conductor to the pulse generator which is usually implanted subcutaneously in the pectoral region. The system can be controlled after the implantation by telemetry.
The present technique only allows for exploration and stimulation of linear tracts of brain tissue. The placement of the electrode is therefore critical, and if the desired target is not reached in the first attempt, a second tract must be made with a statistical doubling of the surgical risk. The related art also described the use of five simultaneous tracts to carry out electro-physiological microcellular recording to determine the optimal target area followed by retracting the five microelectrodes and implanting up to five electrodes per stimulation site. The probability of surgically induced bleeding would accordingly be expected to be increased fivefold.
On the basis of the techniques known in the art, it is the object of the invention to provide an improved electrode device and an implantation method capable of providing a more accurate electro-physiological stimulation than the already existing techniques. In particular, the object is to provide a more accurate determination of the target area in the brain tissue. Furthermore, the object is to reduce the risk of side effects potentially caused by an electrical treatment with deep brain stimulation (DBS).
The invention consist of a multifunction electrode device for neural tissue stimulation, in particular for deep brain stimulation, comprising an elongated flexible electrode body having a head section that is provided with a plurality of electrode conductors with associated electrical connections imbedded in the elongated body, wherein a stilette is provided in the elongated body, said stilette comprising an insulating coating around an electrically conductoring core and an exposed microtip where said tip of the stilette can be advanced through the tip of the electrode body for the performance of microelectrode recordings.
This will allow for a more accurate determination of the desired target area than with the existing test stimulation using the electrode conductors. The procedure of electro-physiological recording and permanent electrode implantation can furthermore be made in one step if the desired target is reached.
In the preferred embodiment of the electrode device according to the invention, the stilette is made of tungsten. Moreover, the stilette is preferably provided with an electrically isolated body of plastic polymer or the like with an exposed tip, preferably 1 &mgr;m or more in diameter, and the stilette of the electrode device could be connected to a microdrive in order to allow for both intracellular and extracellular electro-physiological recordings.
The elongated electrode body is provided in an inflexible insertion tube for the insertion of the electrode device to the determined implant position. This insertion tube can be made of stainless steel or other suitable biochemically inert material. By the use of this stiff, straight cartridge tube, the electrode can be guided into place, whereafter the flexible electrode device is advanced through the tube. Subsequently, the tube is retracted and the electrode is left in its position.
In a second embodiment, the head section of the elongated body is provided with a tension bend, preferably at a length of 2-50 mm and a bending angle between 1°-179°. Hereby, the electrode is provided with a bent configuration in its resting position. The flexible electrode is inserted into place in the straight insertion tube where it is positioned in a tensioned straight configuration. As the insertion tube is retracted and the electrode device is thereby left exposed, the electrode device will take on its natural form, i.e. its bent configuration.
This embodiment of an electrode device, according to the invention, relates to the case where no or suboptimal stimulation effect is achieved in one tract. An electrode with a tension bent tip is then introduced through the steel tube of the mandrin and as the tip exits from the steel tube, it will bend at the predetermined angle in any desired 360 degree direction. By retracting the electrode into the steel tube of the mandrin, advancing it and introduction the bending electrode tip again, a cylindrical volume of nervous tissue can be examined with regard to the optimal permanent electrode placement.
The tension bend in this embodiment of the invention comprises a string of silicone, resorbable biocomposite or any other suitable inert plastic polymer denser on either the concave or convex side of the bend. Hereby, the desired tension effect can be achieved together with the required flexibility of the electrode device.
In a third embodiment of the electrode device, according to the invention, the head section comprises two or more bendable electrode legs, each tip of said bendable electrode legs being provided with an electrode conductor. Upon introduction of the electrode device, the two or more bendable legs will bend at a preferred angle out into the nervous tissue as they exit from the steel tube of the mandrin. One kind of this electrode device consists of four legs with a monoploar electrode conductor at each end. An additional electrode conductor is placed just over the bifurcation of the electrode legs. This will allow macrostimulation of a volume of nervous tissue that is tetrahedral in shape. The tension bend of each individu
Sunde Niels
Sørensen Jens Chr.
Dvorak Linda C. M.
Merchant & Gould P.C.
NeuroKinetic ApS
Ruddy David
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