Stereotactic Radiosurgery Reduces Tremor, Complications in Parkinson's and Essential Tremor

Susan Jeffrey

November 06, 2009

November 6, 2009 — Results from a long-term cohort study in patients with medically refractory Parkinson's disease (PD) and essential tremor (ET) suggest that stereotactic radiosurgery (SRS) provides outcomes comparable to deep brain stimulation (DBS) and radiofrequency in terms of tremor relief and complications.

At a median follow-up of 7 years, about 85% of 183 patients with PD and ET who were treated with SRS had complete or significant resolution of tremors, which is comparable to what is seen with the other approaches. Three patients experienced transient hemiparesis and speech difficulty caused by edema at the surgery site that resolved; there were no cases of hemorrhage, infection, or death.

"The big plus to Gamma Knife is that it's noninvasive, and you get the same tremor relief and much lower complication risks," coauthor Rufus Mark, MD, a radiation oncologist at the Joe Arrington Cancer Center and Texas Tech University in Lubbock, told Medscape Neurology.

"In view of these long-term tremor resolution results and low complication risks, [SRS] should be considered as a primary initial treatment option in medically refractory tremors," the authors conclude.

The findings were presented at the American Society for Radiation Oncology 51st Annual Meeting.

Eradicating Tremor

The target in this setting is the ventralis intermedius nucleus, Dr. Mark explained. "If you have a patient with tremor and you can get to that nucleus and eradicate it with different surgical procedures, you can stop the tremor," he said. DBS and radiofrequency are also used for this, with about an 85% tremor relief rate. "The problem with both of those approaches is you run about a 3% to 4% bleeding risk and a 5% to 6% infection risk," he noted.

SRS is an external beam radiation therapy sometimes known by brand names, including Axesse (Elekta), CyberKnife (Accuray), Gamma Knife (Elekta), Novalis (BrainLab), Primatom (Siemens), Synergy (Elekta), X-Knife (Radionics), TomoTherapy (TomoTherapy), and Trilogy (Varian). In this series, the Gamma Knife was used.

Between 1991 and 2007, 183 patients underwent magnetic resonance imaging (MRI) and SRS thalamotomy for medically refractory PD or ET. A single dose of 140 Gy was used. Pre- and postoperative blinded assessment was done by a team of independent examiners using the Unified Parkinson's Disease Rating Scale and the Clinical Rating Scale for Tremors.

At follow-up of 7 years (range, 2 – 17 years), 154 (84.2%) of the 183 patients of the cohort had complete or significant reduction in tremors. Of the 116 PD patients, 96 (82.8%) had near or complete tremor reduction; of the 67 ET patients, 58 (86.6%) had near or complete tremor resolution, which was not a significant difference (P = .54).

Three patients had MRI-proven edema associated with transient hemiparesis and speech difficulty; in 2 of these patients, symptoms resolved with the use of steroids. "They regained use of the side that was affected fully, and we got them off steroids," Dr. Mark noted.

The third patient required more aggressive therapy with hyperbaric oxygen for 6 weeks, he noted. "So there really haven't been, in my experience, permanent long-term deficits from it."

One limiting factor for this therapy, however, might be the lack of access for neurosurgeons to the technology, Dr. Mark noted. "I think there are roughly 120 Gamma Knife systems across the country."

DBS Still First Choice for Now

Study coauthor Harold Smith, MD, a neurosurgeon at the Joe Arrington Cancer Center and Texas Tech University, told Medscape Neurology that at this point, he still would use DBS for the average patient who is otherwise in good health.

"But there's a subset of patients out there who, for various reasons, just aren't good candidates," he said. Reasons include advanced age, a history of severe cardiovascular or renal disease, or other underlying health problems that might make the procedure too risky, Dr. Smith added. "In those people, the thalamotomy is far easier to tolerate and less dangerous."

Although it offers many potential advantages over DBS, such as no general anesthetic or expensive implanted device, thalamotomy still has some limitations in terms of accuracy, he says.

"With DBS, before we put the permanent electrode into that same area, we sample the different regions nearby — 2 mm anterior, 2 mm lateral, 2 mm posterior — and actually have direct evidence of where that nucleus is and can shift appropriately in the direction where we see more of the electrical activity, and that's very reassuring," Dr. Smith said. "You don't have that currently with the way that Gamma Knife is done now."

However, results with thalamotomy are still very good, localizing the target with anatomic measurements on MRI, he added. The SRS approach may also offer the possibility of treating tremor in countries in which the socioeconomic climate prohibits purchase and maintenance of expensive DBS systems.

Largest Open-Label Experience

Asked for comment on these findings, Kapil Sethi, MD, professor of neurology and director of the Movement Disorders Program at the Medical College of Georgia in Augusta and a member of the editorial advisory board for Medscape Neurology, pointed out that radiosurgery has been used for more than 10 years in the treatment of movement disorders, but the present study is the largest open-label study to date.

"While the results appear to be encouraging, one has to use caution," Dr. Sethi said. "The thalamic lesion may be effective and safe for certain tremors but may have a limited effect on the bradykinesia and dyskinesia — problems that can be disabling."

He cautioned as well that these results should not be extrapolated to mean that pallidal or subthalamic lesioning with radiosurgery is safe. However, he concluded, "We await the full publication with interest."

The authors have disclosed no relevant financial relationships.

American Society for Radiation Oncology 51st Annual Meeting: Abstract 1010. Presented November 2, 2009.

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