Parkinson's disease, which results from the death of nerve cells in the brain, is a chronic, degenerative neurological disorder. Since the risk of developing the disease increases with age, research indicates that one in 100 people over the age of 60 suffer from this debilitating disease. It affects more than 5 million people worldwide.
Motor impairments—the disease's cardinal symptoms—include resting tremor, uncontrolled movement (dyskinesia), slowness of movement (bradykinesia), rigidity (muscle stiffness), and postural instability. Non-motor symptoms include sleep difficulties, loss of sense of smell, constipation, speech and swallowing problems, and low blood pressure when standing. There may also be mood disorders and cognitive impairment ranging from mild memory difficulties to dementia.
The area of the brain that is most affected by Parkinson’s disease is the substantia nigra in the brainstem. Nerve cells lost there are the ones that produce dopamine, a chemical involved in communication to the part of the brain that controls movement and coordination. As the disease progresses, the amount of dopamine produced in the brain decreases, leaving the patient unable to control movement normally, resulting in tremor, stiffness of the limbs, slowed movements and imbalance.
Currently there is no cure for Parkinson’s disease—the therapies listed here provide only symptomatic improvement.
Drug therapy involves stimulating communication to the motor part of the brain. Different classes of drugs can provide more dopamine to the brain (levodopa therapy), reduce dopamine breakdown (MAO-inhibitors or COMT-inhibitors), or mimic the effects of dopamine (dopamine agonists). As the disease progresses, there is a need to use the most potent medication, levodopa therapy. However, within a few years of initiating levodopa therapy, most patients develop motor fluctuations (on-off periods) and dyskinesias in addition to treatment refractory Parkinson's disease symptoms, like freezing and dementia. Dyskinesias are involuntary movements that represent the most challenging of the drug therapy complications faced by Parkinson’s disease patients. Even with optimal intervals and dosages of medication, the amount of time spent with good motor control declines in late-stage Parkinson's disease, and it is at this point that patients consider surgical options to improve their quality of life.
Deep Brain Stimulation
Implantation of a DBS device involves creating an opening in the patient’s skull and inserting electrodes into a specific area in the brain (the globus pallidus or subthalamic nucleus). Then the surgeon implants the stimulator under the skin of the patient’s collar bone and tunnels the electrodes under the skin of the neck to connect them to those implanted in the brain. Small electrical pulses emitted from the DBS device block some of the Parkinson's symptoms and reduce the adverse effects associated with prolonged use of drugs. DBS is the most common surgical intervention used to treat Parkinson’s disease.
Lesioning is a procedure whereby a small volume of tissue is destroyed. In a lesioning procedure done for treatment of Parkinson’s disease, the targeted cells are interfering with motor function, and destroying these cells can improve the patient’s residual motor capacity. The following procedures can be done by radiosurgery or radiofrequency ablation:
- Using stereotactic radiosurgery, a very high dose of ionizing radiation is delivered to a predefined small volume in the brain thereby destroying the vast majority of living cells in this volume.
- In a radiofrequency ablation procedure, a small volume in the brain is heated via a needle inserted through a small opening in the skull. This temperature rise cooks and kills the living cells by heat denaturation of the cell proteins, just like cooking an egg.
Focused Ultrasound Treatment
Focused ultrasound is a completely non-invasive way to perform the lesioning procedure described above without exposing the patient to potentially harmful ionizing radiation. Using this treatment modality in conjunction with image guidance, the physician directs a focused beam of acoustic energy through the patient’s scalp, skull, and brain to thermally coagulate a small area of the brain, thereby destroying targeted tissue without damaging nearby tissue or the tissues through which the beam passes on its way to the target.
Using magnetic resonance imaging (MRI) thermometry during the focused ultrasound procedure, the physician is able to control the location and extent of the thermal tissue destruction in real time.
Focused ultrasound is being studied to treat two symptoms of Parkinson’s through lesioning of one of two target areas of the brain:
- Parkinsonian tremor – lesioning target in the thalamus (thalamotomy)
- Parkinsonian dyskinesia – lesioning target in the globus pallidus (pallidotomy) or subthalamic nucleus
At this time, focused ultrasound is only being assessed to treat one side of the brain, so it will affect tremor or dyskinesia unilaterally.
Focused ultrasound offers several potential benefits:
- Focused ultrasound treatment is non-invasive just like radiosurgery; however, its therapeutic effects are immediate and it does not have the risks or limitations of ionizing radiation.
- Compared to radiofrequency ablation, focused ultrasound is non-invasive and therefore has significant reduced risk for infection. Also as focused ultrasound is done under closed loop thermal feedback, it is more likely to damage only targeted tissue and spare non-targeted healthy brain.
- Compared to implantation of a deep brain stimulation device, focused ultrasound is a single procedure, and does not require subsequent procedures to replace batteries. It also does not involve the collateral damage to healthy tissue or the risk of blood clots and infections associated with implanting a foreign body.
In addition to lesioning, pre-clinical studies suggest focused ultrasound may be able to reversibly open the blood-brain barrier to improve the delivery of drugs like dopamine, gene therapy or even stem cells to targeted areas of the brain.
This trial has completed enrollment for patients with tremor-dominant Parkinson’s (thalamotomy) disease.
Parkinson's dyskinesia (pallidotomy)
A study evaluating the safety and initial efficacy of focused ultrasound for the treatment of Parkinsonian dyskinesia (pallidotomy) is ongoing in the US, Canada and Korea. Additional US sites may follow. This study is being conducted through the collaboration and funding from the Michael J. Fox Foundation for Parkinson's Research.
To inquire about this trial at the University of Virginia, contact Amy Warren at (434) 243-1435 or email at .
To inquire about this trial at the University of Maryland, contact Charlene Aldrich at (410) 328-5332 or email at
To inquire about this trial at Sunnybrook Health Sciences Center in Toronto, contact Nadia Scantlebury at 416-603-5800 ext 6121 or email
To inquire about this trial at Yonsei University in Korea, contact Jin Woo Chang, MD at 82-2-2228-2150 or email at
Regulatory Approval and Reimbursement
The ExAblate system manufactured by InSightec is approved in Europe for treating tremor-dominant Parkinson's Disease. The treatment is not reimbursed by medical payers at this time in Europe.
ExAblate Neuro by InSightec LTD
Supersonic Imagine, Inc. - Aix-en-Provence, France
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Click here for additional references from PubMed.
Animated treatment video courtesy of Insightec