Public Defence: Silje Kristin Bjerknes Silje Kristin Bjerknes at Institute of Clinical Medicine will be defending the thesis “Subthalamic deep brain stimulation in Parkinson’s disease – studies on effects and complications” for the degree of PhD (Philosophiae Doctor).

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Photo: Guro Sommer Værland

Due to copyright reasons, an electronic copy of the thesis must be ordered from the faculty. In order for the faculty to have time to process the order, it must be received by the faculty no later than 2 days prior to the public defence. Orders received later than 2 days before the defence will not be processed. Inquiries regarding the thesis after the public defence must be addressed to the candidate.

Trial Lecture – time and place

See Trial Lecture.

Adjudication committee

  • First opponent: Professor Håkan Widner, Lund University, Sweden
  • Second opponent: Professor of Neurology Elena Moro, Université Grenoble Alpes, France
  • Third member and chair of the evaluation committee: Professor II Angelika Sorteberg, University of Oslo

Chair of the Defence

Professor II Morten Carstens Moe

Principal Supervisor

Professor II Mathias Toft, University of Oslo


Deep brain stimulation of the subthalamic nucleus (STN-DBS) is an established treatment for advanced Parkinson's disease, and improves motor symptoms and fluctuations. However, there are still unanswered questions about the surgical method and long-term effects, in particular regarding the use of microelectrode registration to guide electrode placement and how this affects the efficacy and safety of treatment. Based on this, a prospective, randomized, double-blind study was designed; the Norstim study.

We assessed whether the intraoperative use of multiple versus single microelectrode recording affected the improvement of motor symptoms and quality of life. All the patients were improved after one year of treatment, for motor symptoms and fluctuations, activities of daily living and quality of life. There was a greater improvement in motor symptoms in the multiple microelectrode group after one year, and we found no significant difference in serious adverse events.

After 5-years of STN-DBS we observed a lasting and excellent effect on tremor, motor fluctuations and sleep. Doses of dopaminergic drugs were still at about 50% of the preoperative level. Verbal fluency and executive functions worsened more in the first year than in the following four years, and may be more directly related to the surgery than the reductions in the other cognitive domains. Higher age was the most important preoperative factor predicting physical dependence at five years post-surgery.

Infections are one of the most common complications of DBS treatment. We found infections in relation to 5.6% of procedures. More than half of the infections developed within the first month. Staphylococcus aureus was the most frequent agent, and these infections were more likely to have earlier onset, a more aggressive development and lead to hardware removal more often than infections by other bacterial species. No patient specific risk factors were identified.

Additional information

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Published May 27, 2022 1:12 PM - Last modified June 13, 2022 8:06 AM