What are the benefits of DBS surgery? - Best Neurosurgery Hospital in India

When should one consider surgical therapy? 
 
For patients with early Parkinson's disease, levodopa (sinemet) and other antiparkinsonian medications are usually effective for maintaining a good quality of life. As the disorder progresses, however, medications can produce disabling side effects. Many patients on long-term levodopa develop troublesome dyskinesias, excessive movements that often cause the limbs and body to writhe or jump. In addition, their dose of levodopa no longer lasts as long as it once did. This may lead to "on-off fluctuations," a condition in which the ability to move changes unpredictably between a mobile ("on"), state when medication seem to work, and an immobile ("off") state in which little effect of medication is apparent and normal movement is very difficult. When patients no longer have an acceptable quality of life due to these shortcomings of medical therapy, surgical treatment should be considered. 
 
What are the different types of surgery for Parkinson's disease? 
 
There are several different types of surgery for Parkinson's disease. The first surgical procedures developed were the ablative, or brain lesioning, procedures. Examples of lesioning surgery include thalamotomy and pallidotomy. Lesioning surgery involves the precisely controlled destruction, using a heat probe, of a small region of brain tissue that is abnormally active. It produces a permanent effect on the brain. In general, it is not safe to perform lesioning on both sides of the brain. 
 
We continue to perform some lesioning surgeries for patients who desire it, although in our practice lesioning has been largely replaced by deep brain stimulation (DBS). DBS surgery involves placing a thin metal electrode (about the diameter of a piece of spaghetti) into one of several possible brain targets and attaching it to a computerized pulse generator, which is implanted under the skin in the chest (much like a heart pacemaker). All parts of the stimulator system are internal; there are no wires coming out through the skin. To achieve maximal relief of symptoms, the stimulation can be adjusted during a routine office visit by a physician or nurse using a programming computer held next to the skin over the pulse generator. Unlike lesioning, DBS does not destroy brain tissue. Instead, it reversibly alters the abnormal function of the brain tissue in the region of the stimulating electrode.

 
Many patients inquire about the "restorative" therapies, a category of procedures which includes transplantation of fetal cells or stem cells, growth factor infusion, or gene therapy. These procedures attempt to correct the basic chemical defect of Parkinson's disease by increasing the production of dopamine in the brain. In the future, restorative therapies will hopefully emerge as effective and possibly curative interventions for Parkinson's disease. Growth factor therapy for Parkinson’s disease

 
What are the possible brain targets for DBS?
 
There are now four possible target sites in the brain that may be selected for placement of stimulating electrodes: the internal segment of the globus pallidus (GPi), the subthalamic nucleus (STN), the pedunculopontine nucleus (PPN), and a subdivision of the thalamus referred to as Vim (ventro-intermediate nucleus). These structures are small clusters of nerve cells that play critical roles in the control of movement. Thalamic (Vim) stimulation is only effective for tremor, not for the other symptoms of PD. Stimulation of the globus pallidus or subthalamic nucleus, in contrast, may benefit not only tremor but also other parkinsonian symptoms such as rigidity (muscle stiffness), bradykinesia (slow movement), gait problems, and dyskinesias 

How does DBS work? 
 
The theoretical basis for DBS of the GPi or STN in PD was worked out in the late 1980's and early 1990's. In Parkinson's disease, loss of dopamine-producing cells leads to excessive and abnormally patterned activity in both the GPi and the STN. "Pacing" of these nuclei with a constant, steady-frequency electrical pulse corrects this excessive and abnormal activity. DBS does not act directly on dopamine producing cells and does not affect brain dopamine levels. Instead, it compensates for one of the major secondary effects of dopamine loss, the excessive and abnormally patterned electrical discharge in the GPi or the STN. The exact mechanism by which the constant frequency stimulation pulse affects nearby brain cells has not been determined. 
 
How is the surgery performed?
 
There are several available surgical methods. In the most common method, implantation of the brain electrode is performed with the patient awake, using only local anesthetic and occasional sedation. The basic surgical method is called stereotaxis, a method useful for approaching deep brain targets though a small skull opening. For stereotactic surgery, a rigid frame is attached to the patient's head just before surgery, after the skin is anesthetized with local anesthetic. A brain imaging study (MRI or CT) is obtained with the frame in place. The images of the brain and frame are used to calculate the position of the desired brain target and guide instruments to that target with minimal trauma to the brain. After frame placement, MRI/CT, and calculation of the target coordinates on a computer, the patient is taken to the operating room. At that point an intravenous sedative is given, a Foley catheter is placed in the bladder, the stereotactic frame is rigidly fixed to the operating table, a patch of hair on top of the head is shaved, and the scalp is washed. After giving local anesthetic to the scalp to make it completely numb, an incision is made on top of the head behind the hairline and a small opening (1.5 centimeters, about the size of a nickel) is made in the skull. At this point, all intravenous sedatives are turned off so that the patient becomes fully awake. 
 
To maximize the precision of the surgery, we employ a "brain mapping" procedure in which fine microelectrodes are used to record brain cell activity in the region of the intended target to confirm that it is correct, or to make very fine adjustments of 1 or 2 millimeters in the intended brain target if the initial target is not exactly correct. The brain mapping produces no sensation for the patients, but the patient must be calm, cooperative, and silent during the mapping or else the procedure must be stopped. The brain's electrical signals are played on an audio monitor so that the surgical team can hear the signals and assess their pattern. The electronic equipment is fairly noisy, and the members of the surgical team often discuss the signals being obtained so as to be sure to interpret them correctly. Since each person's brain is different, the time it takes for the mapping varies from about 30 minutes to up to 2 hours for each side of the brain. The neurological status of the patient (such as strength, vision, and improvement of motor function) is monitored frequently during the operation, by the surgeon or by the neurologist. 
 
When the correct target site is confirmed with the microelectrode, the permanent DBS electrode is inserted and tested for about 20 minutes. The testing does not focus on relief of parkinsonian signs but rather on unwanted stimulation-induced side effects. This is because the beneficial effects of stimulation may take hours or days to develop, whereas any unwanted effects will be present immediately. For the testing, we deliberately turn the device up to a higher intensity than is normally used, in order to deliberately produce unwanted stimulation-induced side effects (such as tingling in the arm or leg, difficulty speaking, a pulling sensation in the tongue or face, or flashing lights). The sensations produced at high intensities of stimulation during this testing are experienced as strange but not painful. We thus confirm that the stimulation intensity needed to produce such effects is higher than the intensity normally used during long-term function of the device. 
 
Once the permanent DBS electrode is inserted and tested, intravenous sedation is resumed to make the patient sleepy, the electrode is anchored to the skull with a plastic cap, and the scalp is closed with sutures. The stereotactic headframe is removed. The patient then receives a general anesthetic to be completely asleep for the placement of the pulse generator in the chest and the tunneling of the connector wire between the brain electrode and the pulse generator unit. This part of the procedure takes about 40 minutes. . 
 
 
Why must patients be awake for part of DBS surgery? 
 
Using the standard, microelectrode guided technique for DBS surgery, brain mapping is performed using microelectrodes. The brain mapping procedure is much harder to do if the patient is under a general anesthetic or strong sedative. In addition, the procedure is safer if the patient's neurological function (speech and voluntary movement) can be checked periodically during the procedure, which is only possible in an awake patient. For patients undergoing surgery in our investigational interventional MRI protocol, general anesthesia is used for the whole procedure, as the MR images take the place of electrical mapping and monitoring of neurological function. 
  
What are the benefits of DBS surgery? 
 
The major benefit of DBS surgery for PD is that it makes movement in the off-medication state more like the movement in the on-medication state. In addition, it reduces levodopa-induced dyskinesias, either by a direct suppressive effect or indirectly by allowing some reduction in medication dose. Thus, the procedure is most beneficial for Parkinson's patients who cycle between states of immobility ("off" state) and states of better mobility ("on" state). DBS smoothes out these fluctuations so that there is better function during more of the day. Any symptom that can improve with levodopa (slowness, stiffness, tremor, gait disorder) can also improve with DBS. Symptoms that do not respond at all to levodopa usually do not improve significantly with DBS. Following DBS, there may be a reduction, but not elimination, of anti-Parkinsonian medications. At present, we believe that DBS only suppresses symptoms and does not alter the underlying progression of Parkinson's disease