Fig. 1. Picture showing the electrodes and implantable pulse generator  
   
Deep Brain Stimulation is an alternative to ablative surgeries conventionally offered for Parkinson's disease and other related movement disorders. The common targets for DBS surgery within the brain, for movement disorder include, subthalamic nucleus (STN) for Parkinson's disease, ventro-intermedius nucleus of thalamus for tremors, and pallidum for dystonia. Though each of this target sites can be used for different movement disorder, we believe that these are best for the respective disease as indicated.
 
   
The therapy of Deep Brain Stimulation requires additional expertise over conventional stereotactic techniques that are required for functional neurosurgical procedures for movement disorder. It requires careful understanding of the principles of DBS, understanding of the disease being treated and combining the medical therapy along with stimulation to achieve smooth control of the disease. Jaslok Hospital & Research Center has been able to develop a multi-disciplinary team to undertake this therapy of DBS. It has performed large number of surgeries for Parkinson's disease and other movement disorder during the past few years. The Multi-disciplinary team includes Movement Disorder Neurologist Dr. Mohit Bhatt, Neuroradiologist Dr. Srinivas Desai and Dr. Kohli and Functional Neurosurgeon Dr. Paresh Doshi. This team is supported by the presence of research fellow, occupational therapist, physiotherapist and anaesthesiologist. At present this centre has the largest experience of DBS surgeries in Asia.
 
    
The advantage of DBS over lesional surgeries is that there is no destruction of intracranial nuclei, thus, virtually leaving the patient and his brain intact and available for any future therapies that may come up. The morbidity of the stimulation procedure is also less than lesional surgeries. DBS leads are programmed with the help of an external programmer. This gives the surgeon flexibility in optimizing the current and electrode contacts in each individual patient to suit his requirements. 
 
   
On the downside, the therapy as mentioned above requires high level of surgical expertise that may not be available at many centres. The other disadvantage is a close follow-up, though not frequent, that is required in order to achieve good and sustained control of the disease. This is not the case in lesional surgeries as patients can be followed up at their respective centres after the surgery. The therapy is also more costly than the lesional surgeries. 

The surgical steps for a standard STN stimulation procedure are described. The surgeries for thalamic and pallidal targets are performed in a more or less similar manner. 
   

The surgery is performed using CRW (Cosman-Robert Wales) stereotactic system. The stereotactic frame is fixed to the patient's head under local anaesthesia. The anatomical target localization is performed using computerized tomography (CT) and magnetic resonance imaging (MRI). An inversion recovery, sagittal MRI is obtained to identify the anterior commissure (AC) and posterior commissure (PC). A heavily T2 weighted, coronal MRI sequence is then obtained perpendicular to the AC-PC plane. The STN is typically identified on a slice 2mm posterior to the mid-commissural point. Usually this also correlated with the anterior margin of the red nucleus. STN target is identified 2 mm posterior to the midcommissural point and 11-12 mm lateral and 4mm inferior to this plane. Axial computerized tomography (CT) scan is performed to double-check the MRI co-ordinates. Once the anatomical target is calculated, the stimulating electrode is inserted through a pre-coronal burr hole. Motor stimulation is performed at 5 Hz. frequency and the sensory stimulation is performed at 100 Hz. frequency. Stimulating electrode is used to stimulate the STN and gauge patient's response to both motor and sensory stimulation. The neurologist present in the operation theater assessed the improvement in tremors, rigidity and bradykinesia. The site where there is maximal improvement and least side effects is taken as the final position for implantation of DBS lead. Presence of dyskinesia on the table during sensory stimulation is considered to be a positive confirmatory sign for target localization. Once the confirmation of the STN target is obtained, the stimulating electrode is replaced with DBS electrode (Medtronic DBS electrode 3389-40). Both the electrodes are implanted on the same day. On the next day under general anesthesia the pulse generator (Itrel 2 or Kinetra) is implanted in the infraclavicular fossa. Postoperative CT scan is performed to confirm the position of the electrodes. 
 
   
Results


Thirty-five deep brain stimulation surgeries have been performed at Jaslok Hospital & Research Center in past two years. Out of this, there were two thalamic DBS surgeries for tremors and thirty-three subthalamic nucleus DBS surgeries for advanced Parkinson's disease. Recently we have analysed twenty-five patients of DBS with following results. The improvement in the total "off" phase UPDRS score was approximately 60% and 70% respectively at six months and one year follow up. The scores for activities of daily living improved by 43% and 62% at six months and one year follow up respectively. The patients had become independent and were able to resume back their work. The levodopa requirement of these patients was reduced by 10%-80% with an average reduction of more than 50%. Three patients were able to stop all Levodopa medication. This drug reduction helped in alleviating all the levodopa related side effects (dyskinesia, hallucinations, etc.).