Expert Interview

Peter Lewitt, MD, on surgical options for LID in patients with Parkinson disease

An interview with Peter LeWitt, MD


Peter A. LeWitt, MD, is a Professor of Neurology at Wayne State University School of Medicine and Director of the Parkinson Disease and Movement Disorder Program at Henry Ford Hospital in West Bloomfield, Michigan.

Why has deep brain stimulation (DBS) surpassed ablative surgery as the surgical treatment of choice in patients with levodopa-induced dyskinesia (LID)?

Dr. LeWitt: In ablative surgery for LID, a thermo-coagulation lesion is placed in the globus pallidus interna (GPi). This target of therapy was in use before development of DBS as another way to treat involuntary movements complicating control of Parkinson disease with dopaminergic therapy.

The use of DBS has replaced ablative surgery in most centers offering functional neurosurgery because DBS offers far more control of the clinical outcome. The lesion created by ablation is a permanent effect, whether desired or not. If a GPi lesion were to be inaccurately placed, or too small or large, there could be consequences that a patient would have to live with. Furthermore, ablative surgery also had an unacceptably high incidence of dysphagia and dysarthria (speaking and swallowing difficulties) when the pallidotomy procedure was carried out bilaterally. Bilateral DBS can sometimes lead to similar problems, but by adjusting stimulation settings (or even shutting off one pulse generator when a patient is feeding or speaking), such outcomes can be avoided. With some of the stimulation devices currently in use, the DBS implanted pulse generator has an option for multiple stimulation settings to be created.

Most patients with Parkinson disease have bilateral involvement and so need both sides of the brain treated for optimal outcomes. Once DBS became available, pallidotomy carried out bilaterally was recognized to pose unacceptable risks for most patients.

The efficacy of DBS targeted at the GPi also seems to be better than the clinical results of pallidotomy in the earlier era of functional neurosurgery. Being able to change parameters of electrical stimulation (its location, frequency, pulse width, and current delivery) gives the clinician several tools for enhancing precision to tailor clinical effect and in a manner not achieved from pallidotomy. In the United States and elsewhere, electrical stimulation of GPi and other brain targets is the predominant procedure of functional neurosurgery for movement disorders.

Are there situations where ablative surgery is still considered, and if so, what are they?

Dr. LeWitt: Abblative neurosurgery is not widely used in the U.S. or Europe for movement disorders, though it might be utilized in clinical settings where the expensive DBS electrodes and pulse generators are not routinely available. Furthermore, there are patients who have MRI-incompatible situations and who might opt for lesioning the brain for LID (especially is carried out unilaterally) In my experience at a U.S. hospital, these cases are currently quite rare since the risks of a thermoablation would seem to be greater than simply implanting an electrode in the brain.

Magnetic resonance-guided focused ultrasound (MRg-FUS) pallidotomy has emerged as an incisionless ablative technique. What are the pros and cons of that treatment?

Dr. LeWitt: Using MRg-FUS to create ablative lesions in the brain is a promising new direction for accomplishing an outcome of pallidotomy without the need to penetrate the skull and brain surgically. However, not many treatment centers have acquired equipment for this procedure.

The precision of localizing thermal ablations with FUS seems to be much improved over the operative surgical approach – this is because there's real-time MRI guidance that permit the clinician to localize the intended lesion. The methodology of FUS permits good control over the size of the thermocoagulation procedure carried out in the awake patient, who is able to report on any adverse aspects of the localization of the intended lesioning. Whether this new way to achieve pallidotomy will be an improvement over the conventional surgical methods, or whether this procedure (carried out unilaterally) will be equal to DBS outcomes, remains to be studied further.

In the best of scenarios, incisionless surgery will have fewer surgery-associated risks. By avoiding the need for devices that have to be inserted in the brain (and the risks and costs that they impose), that's an appealing prospect for future therapeutics of movement disorders like LID.

What do you believe will be the preferred surgical procedure for LID in the future?

Dr. LeWitt: Thanks to the long experience with DBS of the GPi and the other benefits this technique provides for control of Parkinson disease, I predict that implanted stimulation electrodes will continue to be a predominant treatment option. As an alternative approach, MRg-FUS is currently limited to unilateral use and has far less long-term clinical experience – it should be regarded as still in the developmental stage (and is not an FDA-approved use, even though MRg-FUS use for treating tremor through thalamic lesioning is sanctioned). However, with more research experience and, if safe and effective, its ultimate approval, non-surgical GPi lesioning might become an appealing alternative to DBS. Research with GPi MRg-FUS has already had peer-reviewing reporting as to safety and efficacy. Of course, other options for control of LID are being explored, such as more constant delivery of levodopa and drugs specifically targeting mechanisms of involuntary movements.

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