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Constant - current implant boosts 'on' time in Parkinson's: from the lancet neurology.

Deep brain stimulation with a constant-current implant significantly increased "on" time in patients with Parkinson's disease, with an increase of almost 3 hours more than a group of control patients who had inactive brain implants.

The control group experienced a small improvement immediately after device implantation but a significantly greater one by 3 months after activation a sign that stimulation, not microlesional effects, mostly likely caused the biggest benefit, according to Dr. Michael S. Okun and his colleagues (Lancet Neurol. 2012;11:140-9).

Most often, deep brain stimulation is administered with a voltage-controlled device with variable current.

"Constant-current devices, such as the one used in this study, have theoretical advantages over voltage-driven devices in that the field of stimulation within brain tissue should be stable in size, whereas stimulation fields produced by voltage-driven devices are susceptible to changes in size caused by changing tissue impedance," wrote Dr. Okun, codirector of the University of Florida Center for Movement Disorders and Neurorestoration, Gainesville, and his associates.

The study randomized 101 patients to immediate activation of a constant-current deep brain stimulation device and 35 to delayed activation. The patients were a mean of 60 years old; mean disease duration was 12 years. All received the Libra DBS device, a constant-current subthalamic nucleus stimulator. The study was not blinded both patients and physicians knew who would receive immediate and delayed stimulation.

The primary end point was the change in good-quality on time--that is, free from bother-some dyskinesias.

Patients who underwent active stimulation at the beginning of the trial were assessed at 3, 6, and 12 months. Control padents were assessed at 3 months, after which their stimulation was switched on and they were also assessed at 6 and 12 months.

At 3 months, both groups reported an increase in good-quality on time. The active group's response was significantly better, however, increasing by a mean of 4.27 hours (from 7 to 11 hours), compared with 1.77 hours in the control group (from 7 to 9 hours), Dr. Okun and his colleagues reported.

The responder rate (at least a 2-hour improvement from baseline) was 72% in the active group and 38% in the control group - a significant difference.

Verbal fluency scores worsened similarly in both groups 3 months after device activation. "These results indicate that verbal fluency deficits, the most frequent cognitive side-effect after DBS of the subthalamic nucleus, are probably secondary to surgical implantation," they wrote.

Both groups had significant declines in Ldopa equivalent dosing compared with baseline, but the active group fared significantly better than the control group.

The investigators assessed the groups separately after the control group's stimulation began at 3 months. By the 6-month visit, the active group's good-quality on time remained stable. After 3 months of active treatment, the control group's on time had increased to an extent similar to the treatment group.

At 12 months after the start of the trial, the on time remained steady in the active group and was matched by the control group. The L-dopa equivalent dose also declined similarly in both groups, Dr. Okun and his associates said.


Major Finding: Constant-current deep brain stimulation improved good-quality on-medication time from 7 to 11 hours after 3 months, significantly more than the improvement seen in a control group with inactive implants.

Data Source: A randomized, nonblinded study of 136 patients with Parkinson's disease.

Disclosures: The study was sponsored by the neuromodulation division of St. Jude Medical Inc. All of the authors reported numerous financial disclosures, including six who reported being paid consultants for St. Jude Medical.
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Title Annotation:NEUROLOGY
Author:Sullivan, Michele G.
Publication:Clinical Psychiatry News
Date:May 1, 2012
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