Q 10 DESCRIBE IN DETAIL THE ADVANTAGES AND DISADVANTAGES OF DEEP BRAIN STIMULATION IN PARKINSON DISEASE ?
A 10 INTRODUCTION
1 Deep brain stimulation (DBS) was first used in the 1970s for the treatment of chronic pain.
2 Mixed results and poor electrode design caused a cessation of significant activity in this field in the 1980s, but over the ensuing 20 years, DBS reemerged as one of the most effective treatments for advanced movement disorders.
3 Deep brain stimulation, a form of stereotactic surgery, has become the surgical procedure of choice for Parkinson disease (PD) because -
A ) it does not involve destruction of brain tissue
B ) it is reversible
C ) it can be adjusted as the disease progresses or adverse events occur
D ) bilateral procedures can be performed without a significant increase in adverse events.
4 Continued refinement of the knowledge of basal ganglia circuitry and PD pathophysiology has narrowed the focus of movement disorder surgery to 3 key gray matter structures - the thalamus, the globus pallidus, and the subthalamic nucleus.
5 DBS is used to relieve both parkinsonian tremor and essential tremor.
6 A randomized, controlled trial in 255 patients with advanced PD found that bilateral DBS was more effective than best medical therapy in improving “on” time without troubling dyskinesias, motor function, and quality of life at 6 Months
MECHANISM OF ACTION
A ) Currently, no explanation clearly describes the mechanism of action of deep brain stimulation (DBS), though several hypotheses have been formulated.
B ) High-frequency stimulation may create a global hyperpolarization of the cell membrane, resulting in a loss of excitability.
C ) Alternatively, stimulation may “jam” signal flow out of an abnormally functioning structure.
D ) Antidromic and orthodromic depolarization currents may modulate neuronal activity at sites distant from the stimulation target.
E ) Finally, stimulation-induced disruption of pathologic network activity may explain the effects of DBS on disorders of abnormal movement.
PROCEDURE
1 The deep brain stimulation (DBS) system consists of a lead that is implanted into the targeted brain structure (thalamus, globus pallidus interna, or subthalamic nucleus [STN]).
2 The lead is connected to an implantable pulse generator (IPG), which is the power source of the system that is generally implanted in the subclavicular region of the chest cavity.
3 The lead and the IPG are connected by an extension wire that is tunneled down the neck under the skin
4 DBS provides monopolar or bipolar electrical stimulation to the targeted brain area.
5 Stimulation amplitude, frequency, and pulse width can be adjusted to control symptoms and eliminate adverse events.
6 The patient can turn the stimulator on or off using an Access Review Therapy Controller or a handheld magnet.
7 The usual stimulation parameters are an amplitude of 1-3 V, a frequency of 135-185 Hz, and a pulse width of 60-120 msec.
8 It has been suggested that DBS works by resetting abnormal firing patterns in the brain and thereby bringing about a reduction in parkinsonian symptoms.
9 The response from DBS is only as good as the patient’s best “on” time, with the exception of tremor, which may show greater improvement than is seen with medication; however, after DBS, the amount of daily “on” time is significantly extended.
10 DBS requires regular follow-up for adjustment of stimulation parameters to account for symptom changes due to disease progression and adverse effects.
11 Implantation of the DBS system is performed in 2 stages as follows -
A ) During the first stage, the DBS lead is implanted stereotactically into the target nucleus
B ) During the second stage, the DBS lead is connected subcutaneously to an implantable pulse generator (IPG), which is inserted into a pocket beneath the skin of the chest wall, like a pacemaker
C ) In DBS for Parkinson disease (PD), as in most stereotactic movement disorder procedures, the first stage is performed with the patient awake to allow monitoring of neurologic status.
D ) The stereotactic headframe is applied on the morning of the procedure, and a targeting MRI is performed
12 Magnetic resonance imaging (MRI) of the brain is performed immediately after the procedure to confirm proper electrode placement and to make sure that no hemorrhage has occurred.
13 If the MRI result is acceptable, the patient is returned to the operating room, where the remainder of the device is implanted with the patient under general anesthesia.
14 The electrode is thin (approximately 1.3 mm in diameter) and flexible, so that it moves atraumatically with the brain.
15 The device can be programmed to deliver stimulation in monopolar or bipolar fashion, employing any of the 4 electrode contacts, alone or in combination
16 After proper patient selection and accurate lead location, competent programming of the implanted device is essential for optimizing DBS therapy.
17 After approximately 2 weeks, therapeutic electrical parameters can be set by using a transcutaneous programmer
18 The primary goals of programming are to maximize symptom suppression and minimize adverse effects; minimizing battery drain is a secondary goal.
A ) These goals can be achieved by following a systematic, multistep approach.
B ) The ability to deliver either monopolar or bipolar stimulation using any of the 4 electrode contacts (or combinations thereof) offers the treating physician a great deal of therapeutic flexibility, permitting customized stimulation for each patient.
C ) Moreover, stimulation parameters can be adjusted at any time if needed.
D ) A decade of experience in Europe and the United States indicates that thalamic DBS is equivalent to thalamotomy for tremor suppression.
19 Candidates for STN-DBS include levodopa-responsive patients with medication-resistant disabling motor fluctuations or levodopa-induced dyskinesia (LID) without significant cognitive impairment, behavioral issues, or mood problems.
20 Unilateral or bilateral STN stimulation is indicated in patients with advanced idiopathic PD who are still responsive to levodopa but suffer from severe fluctuations in medication response, tremor, rigidity, or akinesia in the “off” state (ie, when medications are not working) and LID in the “on” state
A ) -analysis found that on average, doses of levodopa equivalents were reduced by 55.9% after STN-DBS; dyskinesia was reduced by 69.1%; daily “off” periods were reduced by 68.2%; and quality of life was improved by 34.5%.
B ) “On” time is also significantly increased, from 27% of the day at baseline to 74% at 3 months.
C ) Improvement is usually stable, at least up to 5 years.
ADVANTAGES
1 The main advantages of deep brain stimulation (DBS) are its reversibility and adjustability.
2 Because the DBS lead is left in place, physicians have ongoing access to the target site, which allows them to adjust stimulation parameters in response to changes in the patient’s condition.
3 If DBS induces unwanted adverse effects, the stimulator can be turned off, adjusted, or removed.
4 If DBS proves clinically ineffective, the patient has not suffered an irreversible lesion to the brain.
5 Additional advantages include the ability to intervene at targets that cannot or should not be treated with neuroablative lesion surgery and the provision of a unique opportunity to study human basal ganglia physiology.
DISADVANTAGES
1 The main disadvantage of DBS is the cost. Currently, the cost of the device is approximately $10,000 per unit.
2 Additional disadvantages include an increased risk of infection due to the presence of implanted hardware and the cost of maintenance (eg, repair or replacement of fractured wires or repeated office visits for stimulation adjustments).
3 Currently, battery exhaustion necessitates replacement of the entire pulse generator, the most expensive component of the system (costing about $8000), every few years
4 Side effects related to stimulation, including paresthesia, dysarthria, and gait disorders, are relatively common though reversible by setting adjustments ( STIMULATION RELATED )
5 Device-related complications, including end of battery life, skin erosion, or infection can be observed and resolved in most cases ( HARDWARE RELATED )
6 Haemorrhages ( 3.9 % ) and Infections ( 3 - 5 % ) - SURGERY RELATED