Brain surgery is an option for advanced PD patients whose symptoms can no longer be adequately managed with medications. The best surgical candidate is someone who:

• Responds well to dopaminergic therapy
• Has motor complications (off periods and dyskinesias) that are limiting factors
• Is otherwise healthy and a good surgical risk.

Advanced age is not necessarily a barrier to surgery, but impaired cognition, including forgetfulness, diminished decision-making ability, and language difficulties, along with gradual loss of brain matter (brain atrophy or shrinkage), make the surgery more risky and decreases the likelihood of an optimal outcome.

 

Depending on the patient, procedure, and skill of the operating team, cognition may be mildly impaired or largely unaffected by the surgery itself. The most commonly reported adverse cognitive effects are reduced decision-making abilities and language impairments.

 

It is impossible to predict the benefit any individual patient can expect from surgery. The general rule of thumb is that the maximum benefit is equal to the best response from a dose of levodopa (minus the effect on dyskinesias). Therefore, if a patients symptoms are 50% better at the peak of a levodopa dose, the surgery is not likely to improve the patients symptoms more than that amount. Importantly though, improvements from surgery are most dramatic during the times the patient is not experiencing the effects of medications (off time). Therefore, surgery may greatly improve the amount of the day during which symptoms are reduced.

 

Types of surgery

There are two surgical procedureslesioning and deep brain stimulationand three target locations in PD surgery: thalamus, globus pallidum internus (GPi), and subthalamic nucleus (STN). Other surgery-based procedurescell transplants, gene therapy, and neurotrophic factor deliveryremain experimental procedures for the treatment of PD.

 

With lesion surgeries, (that is, pallidotomy or thalamotomy) the surgeon uses radio-frequency energy to heat and permanently destroy a pea-sized area within the part of the brain in which there is abnormal activity related to the movement problems. In the United States, lesion surgery has been almost completely replaced by deep brain stimulation.

 

Deep brain stimulation (DBS) uses implanted electrodes to stimulate one or another of these same regions. The electrical stimulation interferes with the abnormal activity, creating the same effect as a lesion. The effect lasts as long as the stimulation continues, but ceases when it is shut off.

 

During needle-guided (stereotaxic) brain surgery, the patient remains awake. This is for two reasons. The first is that the brain itself has no pain sensors, and once the initial incision is made (using a local anesthetic like Novocain), there is no pain. The second is that patients must be able to respond to the surgical teams questions about what they are experiencing during the surgical procedure. The pathway to the target lies close to several other important structures in the brain that may be inadvertently stimulated during the procedure. This may cause unusual sensations such as flashing lights, tingling, or experience of emotions. Patients then report these sensations to the surgeon during the procedure. Avoiding these areas is crucial for successful surgery.

 

Because surgery requires very precise placement of surgical instruments, a three-dimensional frame is attached to the patients head to guide the surgeon. The frame may be uncomfortable and local anesthetic is used to ease the discomfort. Before surgery, patients will also undergo several imaging procedures, in order to identify the target and other landmarks within the brain. Depending on the center, the procedures may include magnetic resonance imaging (MRI) scans, computerized tomography (CT), or ventriculography.

 

Pallidotomy

Until the late 1990s, pallidotomy was the most common type of PD surgery; deep brain stimulation or DBS is now being performed more often. A pallidotomy involves destruction of part of the globus pallidus (GPi), a region of the brain involved with the control of movement. Destroying part of the GPi may help to restore the balance in that area of brain, which normal movement requires. Pallidotomy is performed by insertion of a wire probe into the GPi. Once its placement has been confirmed by electrical tests, the probe heats surrounding tissue by emission of radio waves. The heat destroys nearby tissue. Effects of the surgery are apparent almost immediately. Improvements from pallidotomy range from 70% to 90% reduction of dyskinesias and dystonia, and 25% to 50% for tremor, rigidity, bradykinesia, and gait disturbance. Levodopa dose may be reduced after the surgery, and dyskinesia improvement is based partly on this reduction.

 

Pallidotomy may be unilateral (one-sided) or bilateral (two-sided). Following a unilateral pallidotomy, improvements are primarily to the side of the body opposite to the lesioned side of the brain. Bilateral surgery is possible and improves dyskinesias further, but greatly increases the risk for worsening effects on cognition, swallowing, and speech; hence, it is done very rarely if at all.

 

Adverse effects of pallidotomy may include hemorrhage, weakness, visual deficits, speech deficits, and confusion, but the risk of these is relatively low in centers with an experienced surgical team. Weight gain is very common following surgery.

 

Thalamotomy

Thalamotomy is primarily effective for the treatment of tremor and is therefore used most often in people with PD for whom tremor is the only disabling symptom. During thalamotomy, a neurosurgeon permanently destroys part of the thalamus. (The thalamus is a paired structure deep within the brain that is involved in the control of movement.) In this operation, neurosurgeons use special equipment that allows them to precisely locate a specific area of the thalamus. When thalamotomy is performed, it is usually only done on one side of the brain because operating on both sides of the brain at the same time increases the chances of the patient developing complications, such as problems with vision and speech. This operation used to be done more often, but today, it is rarely performed for the treatment of PD. Instead, it has replaced by subthalamic deep brain stimulation (DBS) because DBS can improve tremor and other symptoms of PD.

 

Deep Brain Stimulation

Unlike lesion procedures, DBS leaves electrodes in place in the brain to deliver continuous stimulation. The electrodes are powered by a programmable stimulator (like a pacemaker), which is implanted in the chest wall. The stimulator is connected to the electrodes by thin wires (leads) that are tunneled under the skin in the neck and scalp. The stimulator can be turned on and off by a magnet waved over the surface. Many patients turn the stimulator off at night or during periods of prolonged activity, to prolong battery life. Batteries can be replaced as needed, generally after 5 years. Since the battery is in the chest wall, brain surgery is not required to replace them.

 

Adjusting the stimulator and medications after electrode implantation is a major time commitment on the part of the neurological team and patient. The maximum effect of the procedure is achieved once that adjustment occurs, which may be weeks or even months after the procedure itself.

 

Risks for DBS procedures include surgical risks (hemorrhage, infection) as well as hardware complications. These include leads breaking, electrode malfunction, stimulator failure and battery failure.

 

Thalamic DBS

Like thalamotomy, thalamic DBS is primarily effective against tremor. Bilateral procedures are possible, but with a higher risk of adverse effects. Compared to thalamotomy, thalamic DBS has a lower risk of severe side effects.

 

GPi DBS

Effects of GPi DBS tend to mimic those of pallidotomy. Dyskinesia improvement is a major effect, along with some improvement in tremor, rigidity, and bradykinesia, primarily in the off-medication state. Bilateral DBS is better tolerated than bilateral pallidotomy.

 

Subthalamic Deep Brain Stimulation ( DBS)

The subthalamic nucleus has become a major target for deep brain stimulation (DBS), with many teams considering it the target of choice for control of PD. It leads to improvement of all major motor features of PD, with improvement of motor scores of 40% to 60% in the off condition, and 10% in the on condition. Levodopa dosage reduction is typically around 30%, with resulting improvement in dyskinesias. Bilateral procedures appear to be superior to unilateral, with only a slightly increased risk of complications.

 

As DBS has become more common, rare but serious neuropsychiatric adverse events have been increasingly reported. Onset or worsening of depression occurs post-operatively in a small percentage of patients, often in those who were at increased risk before the procedure. Suicide, a well-known risk in depressed patients, has been reported in a small handful of patients. Pre-operative neuropsychiatric evaluation and post-operative follow-up is a critical part of patient care.

 

Updated 10/26/06