Definition and Overview
Deep brain stimulation (DBS) is a neurosurgical procedure that controls abnormal neural circuit activity by stereotactically inserting microelectrodes into specific target nuclei of the brain and applying continuous high-frequency electrical stimulation from an implantable pulse generator (IPG) implanted under the skin of the chest.
Since it was first introduced in the treatment of tremor by Benabid et al. in 1987, its effectiveness against Parkinson's disease, essential tremor, and dystonia has been proven in large-scale randomized controlled trials. It has been performed on more than 200,000 patients worldwide, and its indications are still expanding.
Principle and mechanism
Mechanism of Action
The exact mechanism of DBS is not fully understood, but it is understood that high-frequency (130-180 Hz) electrical stimulation modulates abnormal neural activity patterns in the target area. In the past, it was explained as a 'functional lesion' effect, but now a complex mechanism is proposed, including suppression of pathological oscillation, changes in neurotransmitter release, and promotion of neuroplasticity.
stimulus goal
- Subthalamic nucleus (STN): The most common target in Parkinson's disease. It is effective in improving motor symptoms and reducing drug dosage.
- Globus pallidus internus (GPi): Used to control dyskinesia and treat dystonia in Parkinson's disease.
- Ventral intermediate nucleus (VIM): A standard target in the treatment of essential tremor.
Indications
Parkinson's disease
The most representative indication is moderate to advanced Parkinson's disease in which motor fluctuations and dyskinesia occur after drug treatment. In the EARLYSTIM study, DBS showed superior results than drug treatment alone, even in patients with early motor complications.
Essential tremor
VIM-DBS is effective in severe essential tremor that does not respond to drugs (propranolol, primidone), and tremor is significantly reduced in approximately 80-90% of patients.
dystonia
It has been reported that GPi-DBS improves symptoms by approximately 50-70% in generalized or segmental dystonia. It is most effective in primary dystonia caused by DYT1 gene mutation.
expanded indications
Studies are ongoing in obsessive-compulsive disorder (OCD), treatment-resistant depression, Tourette syndrome, and epilepsy, and some have received limited approval.
surgical procedure
Preoperative evaluation
A multidisciplinary team (neurology, neurosurgery, neuropsychology, and psychiatry) comprehensively evaluates the suitability for surgery. The location of the target nucleus is confirmed with a brain MRI, and cognitive function is evaluated with a neuropsychological test.
electrode insertion
Electrodes are accurately inserted into the target nucleus using a stereotactic frame or robotic assistance system. The target location is confirmed electrophysiologically using microelectrode recording. In the case of Parkinson's disease, the traditional method was to perform awake surgery to check real-time symptom changes, but recently, image-guided procedures under general anesthesia are also increasing.
stimulator implant
IPG is implanted subcutaneously under the chest and clavicle, and connected to electrodes in the brain with an extension line that passes under the scalp.
programming
Programming to optimize stimulation conditions (voltage, frequency, pulse width, stimulation contact point) begins 2 to 4 weeks after surgery. It may take several months to find optimal conditions.
treatment effect
Parkinson's disease
In a large randomized controlled trial, STN-DBS improved motor symptoms by approximately 50-70% in the off-medication state. Dyskinesia under drug administration is also reduced by about 60-70%, and the daily dose of levodopa can be reduced by about 30-50%. Even in long-term follow-up of more than 5 years, the effect on tremor and stiffness is maintained, but the effect on walking and speech disorders tends to decrease over time.
dystonia
After GPi-DBS, the Burke-Fahn-Marsden dystonia score improves by about 50-70%, and the difference from Parkinson's disease is that the effect appears gradually over several months.
Side effects and complications
surgery related
Intracranial hemorrhage (1-2%), infection (3-5%), electrode migration, and skin erosion are reported.
stimulus related
Depending on the stimulation conditions, dysarthria, muscle contraction, sensory abnormalities, and balance disorders may occur, but most of them can be controlled by changing the stimulation conditions. Mood changes and impulse control disorders are reported in some patients, so regular follow-up is necessary.
latest trends
Technological advancements such as directional leads, adaptive stimulation (adaptive DBS, aDBS), and MRI-compatible devices are progressing rapidly. Adaptive DBS analyzes brain signals in real time and applies stimulation only when necessary, and is expected to extend battery life and reduce side effects.