DBS of the STN has proven to be a safe, effective treatment for patients with severe tremor, motor fluctuations, or dyskinesia in Parkinson's disease. However, individual outcomes may vary greatly and critically depend on the brain volume being stimulated. Best motor symptom control has been associated with stimulation of the dorsolateral STN, whereas current leaking into adjacent fiber tracts can cause adverse effects such as dysarthria, impaired fine motor control, or oculomotor disturbances.
Conventional DBS systems use ring‐shaped electrodes, which generate an approximately spherical electrical field. In these systems, programming of polarity and stimulation pulse parameters allows only limited control of the shape of the volume of tissue activated. Recently, two acute intraoperative studies have proven the feasibility of horizontal current steering by using novel lead designs, such as segmented or multicontact electrodes. Directed stimulation using these electrodes resulted in increased stimulation thresholds for side effects as compared to standard spherical stimulation 1).
The objective of a study was to investigate whether directional deep brain stimulation (DBS) of the subthalamic nucleus in Parkinson's disease (PD) offers increased therapeutic windows, side-effect thresholds, and clinical benefit.
In 10 patients, 20 monopolar reviews were conducted in a prospective, randomized, double-blind design to identify the best stimulation directions and compare them to conventional circular DBS regarding side-effect thresholds, motor improvement, and therapeutic window. In addition, circular and best-directional DBS were directly compared in a short-term crossover. Motor outcome was also assessed after an open-label follow-up of 3 to 6 months.
Stimulation in the individual best direction resulted in significantly larger therapeutic windows, higher side-effect thresholds, and more improvement in hand rotation than circular DBS. Rigidity and finger tapping did not respond differentially to the stimulation conditions. There was no difference in motor efficacy or stimulation amplitudes between directional and circular DBS in the short-term crossover. Follow-up evaluations 3 to 6 months after implantation revealed improvements in motor outcome and medication reduction comparable to other DBS studies with a majority of patients remaining with a directional setting.
Directional DBS can increase side-effect thresholds while achieving clinical benefit comparable to conventional DBS. Whether directional DBS improves long-term clinical outcome needs to be investigated in the future 2).