The system is implanted by the Stereotactic Neurosurgeon with clinical and electrophysiological guidance by the Movement disorder specialist trained in the procedure.
The neurosurgeon uses a ‘stereotactic head frame’ and imaging (MRI/ CT scan) to map the brain and locate the target within the brain.
The scan is done after fixing the metallic frame on the head. Subsequently, the patient is shifted to the operating room.
The first stage is implantation of the DBS electrodes inside the brain.
The target selected for implantation is an area in the brain called subthalamic nucleus, whose cells function abnormally in PD, resulting in the motor symptoms of the disease.
The patient remains awake and alert during this stage, so that the neurosurgeon and a movement disorder specialist can test the stimulation to maximize benefits and minimize side effects.
The patient’s scalp is anesthetized to minimize discomfort, a small hole (called Burr Hole) is put in the skull and wires are passed through it into the brain.
The brain itself has no nerves to sense pain or discomfort; hence electrodes can be passed through the brain of the awake patient without any discomfort.
The first set of wires passed are called ‘micro-electrodes’. These wires are passed to record the electrical activity from the target.
The target (“Subthalamic Nucleus”, in the case of Parkinson’s disease) has a peculiar pattern of electrical activity, and recording it correctly ensures that the electrodes are placed at the correct position, mapped by the Neurosurgeon from the scans.
This is very important as DBS system implantation is a ‘closed’ neurosurgical procedure (means that the surgery is not done by opening the skull and exposing the brain; instead, it is done through a small hole) and the surgeon is not directly seeing the target while operating.
To double-check and ensure that positioning of the electrode is correct, test current is given and the patient is tested for improvement of Parkinsonian symptoms and signs and also for any unexpected side effects.
During the testing, patients are asked to speak, to move their limbs and hands and to perform simple tasks while test stimulation is done.
Patients are also asked about any side effects (like ‘double vision’, tingling sensation of one side of the body, difficulty to speak out) they might occur during test stimulation.
All these require the patient to remain very alert and co-operative during the procedure.
Improvement of Parkinsonian symptoms and signs without any adverse effects, on giving the test current confirms correct placement of electrodes.
After achieving this, the ‘micro-electrodes’ are removed and the DBS electrode is placed at the same site. The whole procedure is repeated for the other side of the brain.
The next stage is implantation of the Implantable Pulse Generator (Neurostimulator / “Battery”) under the skin over the chest wall. As this does not require the co-operation of the patient and is painful if done without good anesthesia, this part of the surgery is done under general anesthesia.
A device called the Neurostimulator which is similar to a cardiac pacemaker is implanted over the chest wall, under the skin.
It is a device containing a battery and microelectronic circuitry.
It generates electrical signals that are delivered to the brain via a thin wire with electrodes attached at the tip.
The electrodes are implanted in the brain on both sides and the cables that connect it to the neurostimulator are tunneled under the scalp and the skin of the neck.
Deep Brain Stimulation works by high frequency electrical stimulation of the target areas (the Subthalamic Nuclei) deep within the brain that control movements.
These areas function abnormally in PD, resulting in the disabling “motor symptoms” (tremor/ slowness of activities/ stiffness of limbs etc) of the disease.
High frequency electrical stimulation of these areas alters the function more towards normalcy and relieves the motor symptoms.
As the non-motor symptoms of PD are generated by dysfunction of other areas of the brain, they may not be relieved by DBS of the subthalamic nucleus.
Similarly, if the Neurostimulator is switched off for a few hours, the Subthalamic Nucleus goes back to the original abnormal state and all the symptoms will recur. Thus, DBS is not a permanent cure for PD.
The frequency, intensity etc of the stimulation, and the “point” on the tip of the electrode through which the electrical pulses are delivered can be changed in a number of ways to give maximum benefit to the patient. This is called programming and is done by the movement disorder specialist, using a special device.
Programming is much like tuning a radio - the stimulation parameters are adjusted until the optimal effect is obtained.
Stimulation with higher intensities of current / stimulation of certain areas in the subthalamic nucleus can sometimes result in adverse effects like difficulty to speak out, and minor behavioral problems.
The advantage of DBS over the other ‘lesioning’ surgeries mentioned below is that the adverse effects, if they occur, can be abolished / minimized by altering the stimulation parameters.
Programming is done to ensure that the patient gets maximum control of the symptoms of PD at the cost of no or minimum adverse effects.
The initial programming done (usually a few days after surgery) may not give the best results, as surgery related factors (for example, swelling of the brain areas concerned, resulting from the trauma of the surgery) may interfere with it.
The patient often requires re-programming a few weeks later. Minor adjustments can be done by the patient, using the therapy controller unit provided
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