Introduction to Deep Brain Stimulation (DBS)
The modern era of DBS began in 1987 when Alim Benabid published his paper reporting the use of ventral intermediate nucleus (Vim) stimulation for Parkinson’s Disease (PD).
Since then DBS has been used for PD, Dystonia, Essential tremor, psychiatric disorders, and Epilepsy. The last several years have been characterized by many emerging and new indications and new intracranial targets for DBS.
Of particular interest in the treatment for DBS are behavioral and psychiatric disorders, including Tourette’s syndrome, major depression, and obsessive-compulsive disorder (OCD).
Large centers prefer a multidisciplinary approach that will involve a neurologist, a neurosurgeon, a psychologist, a psychiatrist, and a nurse specialist.
Role of the Neurologist
A neurologist plays a central role in the candidate selection process by confirming the diagnosis in PD, and dystonia, He also assesses the severity of symptoms and disability, verifying responsiveness to medications using objective Scales, and instilling realistic patient expectations.
Role of Neurosurgeon
The neurosurgeon and the neurologist work closely to evaluate the benefits and risks of DBS. Together they share the responsibility for evaluating the degree of disability as well as discussing patient expectations. He will evaluate the surgical risks and carefully explain all details of the procedure to the patient and family. Possible complications related to the surgical procedure, the implanted device and the stimulation will also be discussed by the treating neurosurgeon.
Role of psychiatrist
The principal role of the psychiatrist is to identify and treat patients with underlying psychiatric conditions, especially those that may be worsened by DBS. Psychiatric screening as an important safety measure.
In the case of DBS for psychiatric conditions, the psychiatrist will evaluate in detail if the patient is a suitable candidate for surgery. His role will be from evaluation to being part of the surgical team during surgery and in post-DBS programming in these patients.
Role of the Neuropsychologist
A Neuropsychologist is responsible for cognitive and behavioral testing for the patients undergoing DBS surgery. Neuropsychological testing is helpful in excluding patients with dementia. In addition, it can also be helpful for separating medication-induced encephalopathy from true dementia
DBS can be used in the following conditions
- Parkinson’s disease
- Essential and other tremors
- Medically refractory depression and obsessive-compulsive disorders
How does the device work?
Deep brain stimulation (DBS) involves a surgery that implants a device that sends signals to areas of the brain that are responsible for body movements.
Electrodes are placed deep within the brain depending on the symptoms being targeted, and these are connected to a stimulator device.
Electric pulses produced by a neurostimulator are used to regulate brain activity. This device resembles a heart pacemaker. The mechanism of DBS is likely not simply a matter of inhibition or excitation, rather it involves complex changes throughout the entire basal ganglia-thalamocortical network. So basically it’s a high frequency, pulsatile, mono or bi-polar electrical stimulation device that is placed stereotactically in a particular area of the brain with pinpoint accuracy.
Risk factors for DBS
Although there is an impression that younger patients have less surgical risk, no well-defined upper age limit has been set for DBS surgery. However, a majority of centers have arbitrarily utilized an upper age limit of 75 years.
MRI is recommended as part of the pre-surgical evaluation for DBS. MRI helps to exclude patients with atypical symptoms, moderate to severe cortical atrophy, significant vascular white matter changes, and structural lesions.
- Medical Comorbidities
There may be an increased risk for surgery in those having uncontrolled diabetes, heart disease, pulmonary dysfunction and hypertension.
- Patients with Prior Ablative Surgery
DBS can be safely performed in patients who have had prior ablative surgery for PD. However, we need to consider a few parameters such as the size of the previous lesion, lesion location, and responsiveness of symptoms to a levodopa challenge.
The procedure can be done with the patient being awake or under general anesthesia depending on the indication and the surgeon’s preference.
The Patient who will undergo a DBS surgery will have to be evaluated with an MRI, and other necessary investigations. The steps of the surgery will be as follows.
- Attaching the stereotactic frame: This procedure is done by attaching a frame to your head under local anesthesia.
- A Computed Tomography (CT) scan: An imaging CT scan is then done after placing a localizing device over the frame. This helps to identify the exact three-dimensional coordinates of the target area within the brain. These images are then fused with the already planned MRI images to get sub-millimeter accuracy.
- Skin and skull incision: This procedure is done in the operation theatre, and the stereotactic head frame is secured to the operating table. An incision is made over the skin. Small burr holes are made on both sides on the skull using a drill. These holes are to allow the electrodes to pass through.
- Insertion of the electrodes: Through the burr holes, small electrodes are inserted into the brain at a precise depth and angle. During the procedure, the recording electrode can identify which brain cells are firing signals and display waveforms on the computer. The Neurologist will evaluate the clinical response by asking the patient to perform certain simple tasks like counting, moving the fingers and legs, so that the electrodes can be placed in the best possible location where the patient will benefit the most.
- Stimulation of brain cells: The recording electrode is then replaced with a permanent Deep Brain Stimulation electrode or lead. Test stimulation is done, and you will be asked if you feel the symptoms lessen or disappear. The accuracy of the placement of the electrodes is then confirmed using Intraoperative X rays
- Closure: Once the team is satisfied with the placement of the electrodes, the burr hole is sealed, and the scalp incision is closed with staples or sutures, and a bandage is applied.
- Implanting the stimulator: After the initial part of placing the electrodes, the head frame is removed, and the stimulator is implanted under the collar bone.
- Programming the stimulator: Programming is done after a few days from surgery. The stimulator will be programmed, and your medication dosage will be adjusted. You will be required to come for follow-ups every three weeks to optimize the stimulation device.
What is the risk and complication of Deep Brain Stimulation Surgery?
Every surgery comes with its share of risks. General complications include infection(2-4%), Hemorrhage(<3%), seizures(<1%), depression, hardware-related complications, misplaced leads(0-10%), Skin erosion, etc. However, it is a relatively safe procedure with minimal overall risk to life.
Additional surgery may be required for reasons such as breakage of the extension wire in the neck, wear and tear of parts beneath the skin,or removal of the device due to mechanical failure of the device or infection. Battery replacement depends on the type of battery used. For non-rechargeable batteries, the replacement may be needed once every 3-5 years. For the rechargeable batteries, the replacement may last for 12-25 years.
What to expect from DBS surgery?
- It is not a curative surgery but improves the quality of life.
- It is usually done on both sides.
- It improves motor fluctuations.
- Improves tremor, stiffness, bradykinesia,and dyskinesia in the city of the cases.
- May not improve speech, cognition, mood,and behavior.
- Repeated visits to the hospital may be required initially for programming till an appropriate and optimal response is seen, which is usually in the first 6 months.
- Medications may be reduced in many patients, but not in all patients.
Deep Brain Stimulation and psychiatric disorders
DBS has shown promising results in clinical trials when used to treat mood and cognitive disorders such as major depression and Obsessive-compulsive disorder(OCD). Electrodes are placed in specific targeted regions of the brain. Several areas have been identified as target sites for the treatment of refractory depression that is resistant to medical treatment.
Although the precise mechanism is not yet completely understood, DBS can target certain regions and circuits within the brain which may be responsible for some neuropsychiatric illnesses. Also, DBS is a reversible process and the advantage of adjustability. This will enhance the effectiveness of therapy and minimize side effects. Thus, DBS may offer a degree of hope for patients with severe and treatment-resistant neuropsychiatric illness such as depression and OCD
However more work is needed in the field of DBS for psychiatric symptoms currently.