Deep brain stimulation for Parkinson’s disease

Surgical procedures have been used for decades to control the symptoms of Parkinson’s disease (PD). Let’s take a closer look at the most commonly used surgical treatment for PD.

Stereotactic surgery involves accurately accessing specific areas of the brain by assigning x, y, and z coordinates to all points of the brain within a virtual three-dimensional space. This process has been greatly facilitated by computer technology in the modern era.

In the 1950s and 1960s, stereotactic surgery involved the destruction (e.g., lesioning) of various deep brain structures and was relatively effective in the treatment of select diseases (such as PD). Over the past several decades, stereotactic implantation of stimulating electrodes in deep brain structures—known as deep brain stimulation (DBS)—has become the mainstay of PD surgical treatments.

Deep brain stimulation is reversible because it doesn’t result in tissue destruction. It is also adjustable in its effects.

A DBS system is safer than lesioning when planning bilateral procedures because the system can be turned off if there are too many side effects; various neurobehavioral side effects are more common when altering functions on both sides of the brain.

Surgery for DBS involves the accurate placement of stimulating electrodes into important parts of the basal ganglia involved in the control of movement—the subthalamic nucleus (STN) or the globus pallidus internus (GPi). The electrodes are then led out of the skull and under the skin to a pacemaker-like device (known as a pulse generator), which is usually implanted just under the skin below the clavicle.

Patients may have DBS systems placed in one or both sides of the basal ganglia. Unilateral placement will only affect motor symptoms on the opposite side of the body. Since motor symptoms of PD are often initially unilateral, a unilateral system may be placed. If both sides of the body are significantly affected, a bilateral system will need to be placed.

DBS surgery is often performed in stages, particularly if bilateral systems are to be placed.

Surgery is usually performed while the patient is awake to obtain as good of a clinical response as possible. Patients can be tested immediately for placement efficacy, and micromillimeter adjustments can be made in the placement for the greatest reduction in symptoms.

The surgery can last a few hours and includes a microelectrode recording of cellular electrical activity to optimize lead placement. Neurologists and electrophysiologists often assist in determining the best placement of electrodes.

After implantation, the systems are usually checked and adjusted by a movement disorder neurologist. One of the major benefits of a DBS system is that the firing of electrodes of a lead can be adjusted and altered after surgery by telemetric systems. So, if the system is not functioning optimally after surgery, adjustments can be made.

Deep brain stimulation is the most effective at improving typical PD motor symptoms:

• Bradykinesia
• Dyskinesia
• Rigidity
• Tremor

However, DBS may also help some patients with other common PD symptoms:

• Speech disturbances
• Posture disturbances
• Gait disturbances
• Freezing (the temporary and involuntary inability to move)

A DBS system offers significant improvement in PD patients with moderate symptoms, and often remains effective for up to ten or more years.

However, although some research suggests otherwise, there is no evidence that DBS alters the progression of PD. So, the underlying disease still progresses. For this reason, if the system is turned off or becomes dysfunctional, the motor symptoms may be much worse than before DBS treatment because they increase over time.

And DBS has not been shown to improve non-motor symptoms including depression, psychological dysfunction, or dementia in patients with PD.

The procedure is generally quite safe, but there is a small (less than 5%) risk of hemorrhage or infection. Hemorrhage is seldom devastating but may interfere with the success of the procedure. Infection often requires removal of the system and replacement after a period of antibiotic treatment.

You should consider DBS surgery in five types of patients with PD:

1. Patients who are refractory to medical therapy
2. Patients with severe tremors
3. Patients whose primary symptoms are rigidity and bradykinesia
4. Patients who have had a diagnosis of Parkinson’s disease for more than four years
5. Patients who are experiencing gait disturbance and postural instability with freezing and falls

DBS surgery for patients with severe tremors is a bit different; if tremors are the predominant symptom, the electrodes may be placed in the thalamus rather than the subthalamic nucleus.

Classically, the best responders to DBS are patients who responded well initially to levodopa and carbidopa, but later experienced increasing off-period durations and greater on / off fluctuations of symptoms. While some research suggests that DBS should be considered earlier in such patients (without years of increasing dosages and polypharmacy), others recommend trying to hold off on placement until the standard line-up of medications stops being effective.

Contraindications for DBS

Some patients with PD are not good candidates for DBS, including those who have one of the following conditions or characteristics:

• Patients who are over 85 years of age
• Patients who have profound dementia
• Patients experiencing PD-like disorders but not true PD
• Patients in late stages of PD or with severe debilitation
• Patients at high-risk for complications with intracranial surgery (e.g., taking anticoagulants)
• Patients with ipsilateral hemianopsia (proximity of the electrode to the optic tracts can increase the risk of bilateral visual defects)

There are six signs and symptoms that you should look out for in a patient with a DBS implant:

1. Muscle pulling
2. Tingling
3. Eyelid fluttering
4. Visual flashes
5. Changes in phonation
6. Pain

If any of these symptoms occur when the patient’s system is on, they may be the result of excess stimulation to nearby structures, which can be controlled by electronic adjustment of the system. As well, the symptoms could result from migration of the system lead.

If a patient finds one day that they seem to be having no response to their DBS system, first consider a system dysfunction rather than sudden inefficacy. Check that the patient has indeed turned the system on, and then ask about recent falls or heavy exertion.

Patients should refrain from heavy rotational activities and activities with a high risk of falling, as these could cause damage to the system or movement of the leads. X-rays of the system may help determine if movement of the leads has occurred, or if breakage or disconnection within the system has taken place.

If the system dysfunction cannot be readily remedied, refer the patient immediately to a movement disorder specialist. Often the system can be assessed via telemetry by a product representative. They will look for battery depletion and internal system dysfunction.

If the system is believed to be dysfunctional or the battery is depleted, refer to the appropriate neurosurgery team. Batteries usually last around three to five years. Breakages will also require neurosurgical replacement of the broken components.

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