Deep Brain Stimulation Treatment of Parkinson’s Disease Sam Park Brief History Basal ganglia have been targeted for neuromodulation surgery since the 1930s. 1950s: Pallidotomy was the accepted procedure for the treatment of PD. 1960s: Levodopa therapy was introduced - However, many PD patients remain disabled despite best available dopaminergic treatment Limitations of dopaminergic therapy led to a resurgence of new surgical techniques directed at basal ganglia targets in late 1980s, early 1990s. Brief History 1993: Bilateral high-frequency stimulation of subthalamic nucleus (STN) introduced in treatment of advanced PD - Based on new insights into the pathophysiology of basal ganglia derived from experimentation on animal models of PD Siegfried & Lippitz (1994): Introduced DBS of globus pallidus internus (GPi) for treatment of advanced PD Pioneering studies & empirical observations during surgery showed that DBS improved PD patient’s motor function and quality of life. Today, DBS (electrical stimulation of basal ganglia structures via implanted electrodes) has become a non-lesioning alternative to pallidotomy. Relevant Brain Structures Motor Circuit Parkinson’s Disease Intervention Patient Selection Goal: Find ideal patients, where individual benefit > risk of surgery Advanced idiopathic PD with motor complications is main indication for DBS in PD Multidisciplinary approach: 1. Neurosurgeon 2. Neurologist 3. Neuropsychologist Intervention Patient Selection Response to levodopa = best prognostic indicator for DBS suitability Neuropsychological evaluation - Depression - Psychosis Age Full medical assessment Discussion of long-term and short-term effects of DBS Education regarding environmental concerns with implantable devices Intervention Surgical Procedure Precise implantation of stimulation electrode in targeted brain area. Connecting electrode to internal programmable pulse generator Neurobiology Brain areas targeted in DBS: 1. 2. 3. Vim = ventralis intermedius nucleus of the thalamus GPi = posteroventral portion of the internal segment of the globus pallidus STN = subthalamic nucleus Intervention Pre-Operative Stage: Stereotactic Surgery - Locate targeted brain areas Stereotactic frame MRI, CT, or ventriculography Stereotactic atlas Intervention Pre-Operative Stage: Functional Stereotactic Surgery - Electrophysiological exploration of targeted regions via test electrodes - Involves: 1. Microrecording 2. Test-stimulation - Increases accuracy of localization (i.e. finding optimum target in GPi or STN) - Under local anesthesia Intervention Optimal Stimulation Sites: - Dorsolateral STN border - Posteroventral GPi Implantation of Electrode: DBS electrode stereotactically inserted with special rigid guide tube Patient is awake and in the medication-“off” state after 12-hour withdrawal Intervention Implantation of Electrode: Electrode has 4 contacts on its distal end The effects of stimulation from each combination of 2 contacts or monopolarly from each contact are assessed - Determine best contact(s) to use to obtain optimal therapeutic benefit Intervention Electrode-Stimulator Connection: Electrode Extension (passed under skin to chest) Chest: Battery-operated stimulator Patient turns stimulator “on” and “off” by passing magnet over the skin overlying stimulator Typical stimulator settings: - Voltage amplitude: 2-3 V - Pulse width: 90 μs - Stimulation frequency: 130-185 Hz Intervention Electrode-Stimulator Connection: Stimulator parameters adjusted via a computercontrolled probe placed over stimulator Pulse generator can be adjusted post-operatively by telemetry: (1) Electrode configuration, (2) Voltage amplitude (3) Pulse width (4) Frequency Mechanisms of DBS The exact mechanisms underlying the beneficial effects of DBS are still unknown. Logistical fallacy exists. Many hypotheses exist regarding the mechanisms underlying high-frequency stimulation. Mechanisms of DBS 1. HFS may inhibit neurons Synaptic depression by stimulation-induced neurotransmitter depletion. STN HFS suppresses STN neuronal activity Effects of microstimulation on firing of neurons in GPi: - Single, low-intensity stimuli in GPi produced inhibition of GPi neuronal firing rate - High-frequency, low-intensity trains of stimuli caused periods of inhibition - Synaptic inhibition by stimulation of inhibitory afferents to GPi Mechanisms of DBS 2. HFS may excite neurons A subthreshold normal signal, lost in the noise of a deranged neural network, is amplified by the addition of a regular noise (HFS). “Jamming” of information - Constant high-frequency excitation may disrupt any pathophysiological patterns of neuronal activity - Excitation may lead to desensitization or other long-term changes in pre-/post-synaptic excitability of GPi synapses Mechanisms of DBS 3. HFS of STN neurons may lead to hyperpolarization Due to activation of Ca2+-dependent K+ currents Prolonged HFS in rat STN caused prolonged inactivation of volatage-gated Na2+ and Ca2+ channels Similar mechanisms might exist in GPi neurons 4. Depolarization block HFS causes cell to fire, without sufficient time to repolarize the membrane potential Neuronal transmission blocked and firing rates decreased Deuschl et al. (2006) Study A Randomized Trial of Deep-Brain Stimulation of Parkinson’s Disease Design: Unblinded, randomized-pairs trial Participants: 156 patients with advanced Parkinson’s disease and severe motor symptoms Participants were randomly assigned to 2 groups: 1. Deep-brain stimulation of subthalamic nucleus (STN) 2. Best medical treatment Primary end points: Changes from baseline to 6 months Measures: Quality of life = Parkinson’s Disease Questionnaire (PDQ-39) Severity of motor symptoms, without medication = Unified Parkinson’s Disease Rating Scale, part III (UPDRS-III) Deuschl et al. (2006) Study A Randomized Trial of Deep-Brain Stimulation of Parkinson’s Disease Results: Mean PDQ-39 Summary Index Score: Baseline Neurostimulation Group Medication Group 6 months 41.8 ± 13.9 31.8 ± 16.3 39.6 40.2 ± 14.4 Neurostimulation Group: Mean improvements of 9.5 points (25% improvement) from baseline to 6 months Medication Group: No change Neurostimulation resulted in improvements of 24%-38% in PDQ-39 subscales for mobility, activities of daily living, emotional well-being, stigma, and bodily discomfort. Deuschl et al. (2006) Study A Randomized Trial of Deep-Brain Stimulation of Parkinson’s Disease Results: Mean UPDRS-III Score: Neurostimulation Group Medication Group Baseline 6 months 48.0 28.3 ± 14.7 46.8 ± 12.1 46.0 ± 12.6 Neurostimulation Group: Mean improvements of 19.6 points (41% improvement) from baseline to 6 months Medication Group: No change Deuschl et al. (2006) Study A Randomized Trial of Deep-Brain Stimulation of Parkinson’s Disease Conclusion: Subthalamic neurostimulation was more effective than medical management alone for the treatment of patients with advanced Parkinson’s Serious adverse events were more common with neurostimulation than with medication alone - Intra-cerebral hemorhage Limitations: No sham-surgery or placebo control groups used Schüpbach et al. (2005) Study Stimulation of the Subthalamic Nucleus in Parkinson’s Disease: a 5 Year Follow Up Design: 5 year follow up study Participants: 37 patients with PD, treated with bilateral STN stimulation Participants assessed prospectively 6, 24, and 60 months after surgery Measures: Motor assessment: UPDRS-III Activities of daily living: UPDRS-II Neuropsychological and mood assessment: Mattis Dementia Rating Scale, the frontal score, Montgomery-Asberg Depression Rating Scale (MADRS) Schüpbach et al. (2005) Study Stimulation of the Subthalamic Nucleus in Parkinson’s Disease: a 5 Year Follow Up Results: Schüpbach et al. (2005) Study Stimulation of the Subthalamic Nucleus in Parkinson’s Disease: a 5 Year Follow Up Results: Assessment 5 years after surgery: STN stimulation improved activity of daily living by 40% (“off” levodopa) and 60% (“on” levodopa) STN stimulation improved Parkinsonian motor disability by 54% (“off” drug) and 73% (“on” drug) Severity of levodopa related motor complications decreased by 67% No change in MADRS Cognitive performance declined Schüpbach et al. (2005) Study Stimulation of the Subthalamic Nucleus in Parkinson’s Disease: a 5 Year Follow Up Adverse Side Effects: Persisting side effects: eyelid opening apraxia, weight gain, hypomania and disinhibition, dysarthria During 60 month follow up, 6 patients died Limitations: Absence of a control group Conclusions: Long-term post-operative improvement in Parkinsonian motor disability was sustained 5 years after neurosurgery Advantages of DBS Avoid adverse side effects associated with lesioning procedures Does not require deliberate destruction of brain regions Effects of stimulation therapy are reversible - Due to reversibility, does not preclude use of future therapies Can change stimulation parameters to optimize clinical benefit Advantages of DBS Can be safely performed bilaterally (in contrast to ablative procedures) May be the only effect treatment of levodopa-induced dyskinesias The beneficial changes are long-lasting Disadvantages of DBS Adverse side effects related to surgery - Intra-cranial hemorrhage - Pulmonary embolism, chronic subdural hematoma, venous infarction, seizure Hardware related failure - Lead extension fracture, lead migration, short or open circuit, malfunction of pulse generator, infection, etc. Adverse effects related to electrical stimulation - Electrical current could spread into adjacent structures, leading to tonic muscle contraction, dysarthria, paraesthesia, worsening of akinesia, etc. Disadvantages of DBS Post-operative adverse side effects are common - Weight gain Dyskinesia Axial symptoms Eyelid, ocular, visual disturbances Behavioral and cognitive problems (e.g. - Muscle contractions - Paresthesia - Speech dysfunction mood disorders) Long-term complications - Infection or erosion - Tolerance - Pain and discomfort - Sudden loss of effect - Development of dementia Costs of surgery Cannot use sham surgeries as controls Conclusion Overall, I feel that DBS is one of the best and most effective treatment options for advanced Parkinson’s. It is not only safer than many lesioning procedures, but has been empirically shown to reduce levodopa-induced symptoms. Longitudinal studies and randomized control trials have also provided support for its efficacy. However, the procedure may not be suitable for every PD patient. This is especially evident by the careful screening process involved in patient selection, which attempts to identify patients with idiopathic PD and motor complications. Additionally, the fact that the success of the intervention relies heavily on physiological and psychological factors, the assessment process puts great emphasis on the neuropsychological function of the disease. Conclusion Although the pathophysiology of PD has been well studied and determined, there are many aspects which are still unknown. Future research should be directed at the exact mechanisms by which DBS exerts its beneficial effects. It may be possible that one of the hypotheses for the mechanism of action already discussed is in fact correct.