The surgical treatment of Parkinson's disease

Stem Cell-based and Advanced Therapeutic Modalities for Parkinson's Disease: A Risk-effectiveness Patient-centered Analysis

Treatment of Parkinson's disease (PD), the second most prevalent neurodegenerative disorder, is currently considered a challenging issue since it causes substantial disability, poor quality of life, and mortality. Despite remarkable progress in advanced conventional therapeutic interventions, the global burden of the disease has nearly doubled, prompting us to assess the riskeffectiveness of different treatment modalities. Each protocol could be considered as the best alternative treatment depending on the patient's situation. Prescription of levodopa, the most effective available medicine for this disorder, has been associated with many complications, i.e., multiple episodes of "off-time" and treatment resistance. Other medications, which are typically used in combination with levodopa, may have several adverse effects as well. As a result, the therapies that are more in line with human physiology and make the least interference with other pathways are worth investigating. On the other hand, remaining and persistent symptoms after therapy and the lack of effective response to the conventional approaches have raised expectations towards innovative alternative approaches, such as stem cell-based therapy. It is critical to not overlook the unexplored side effects of innovative approaches due to the limited number of research. In this review, we aimed to compare the efficacy and risk of advanced therapies with innovative cell-based and stemcell- based modalities in PD patients. This paper recapitulated the underlying factors/conditions, which could lead us to more practical and established therapeutic outcomes with more advantages and few complications. It could be an initial step to reconsider the therapeutic blueprint for patients with Parkinson's disease.

Developments in the mechanistic understanding and clinical application of deep brain stimulation for Parkinson's disease

INTRODUCTION. Deep brain stimulation (DBS) is a life-changing treatment for patients with Parkinson's disease (PD) and gives the unique opportunity to directly explore how basal ganglia work. Despite the rapid technological innovation of the last years, the untapped potential of DBS is still high.

AREAS COVERED. This review summarizes the developments in the mechanistic understanding of DBS and the potential clinical applications of cutting-edge technological advances. Rather than a univocal local mechanism, DBS exerts its therapeutic effects through several multimodal mechanisms and involving both local and network-wide structures, although crucial questions remain unexplained. Nonetheless, new insights in mechanistic understanding of DBS in PD have provided solid bases for advances in preoperative selection phase, prediction of motor and non-motor outcomes, leads placement and postoperative stimulation programming.

EXPERT OPINION. DBS has not only strong evidence of clinical effectiveness in PD treatment, but technological advancements are revamping its role of neuromodulation of brain circuits and key to better understanding PD pathophysiology. In the next few years, the worldwide use of new technologies in clinical practice will provide large data to elucidate their role and to expand their applications for PD patients, providing useful insights to personalize DBS treatment and follow-up.

Deep brain stimulation for the treatment of drug addiction

Drug addiction represents a significant public health concern that has high rates of relapse despite optimal medical therapy and rehabilitation support. New therapies are needed, and deep brain stimulation (DBS) may be an effective treatment. The past 15 years have seen numerous animal DBS studies for addiction to various drugs of abuse, with most reporting decreases in drug-seeking behavior with stimulation. The most common target for stimulation has been the nucleus accumbens, a key structure in the mesolimbic reward pathway. In addiction, the mesolimbic reward pathway undergoes a series of neuroplastic changes. Chief among them is a relative hypofunctioning of the prefrontal cortex, which is thought to lead to the diminished impulse control that is characteristic of drug addiction. The prefrontal cortex, as well as other targets involved in drug addiction such as the lateral habenula, hypothalamus, insula, and subthalamic nucleus have also been stimulated in animals, with encouraging results. Although animal studies have largely shown promising results, current DBS studies for drug addiction primarily use stimulation during active drug use. More data are needed on the effect of DBS during withdrawal in preventing future relapse. The published human experience for DBS for drug addiction is currently limited to several promising case series or case reports that are not controlled. Further animal and human work is needed to determine what role DBS can play in the treatment of drug addiction.

Efficacy and Safety of Deep Brain Stimulation in the Treatment of Parkinson's Disease: A Systematic Review and Meta-analysis of Randomized Controlled Trials

Deep brain stimulation (DBS) is a neurosurgical procedure indicated for patients with advanced Parkinson's disease (PD). Whether similar benefits may be realized by patients with early PD, however, is currently unclear, especially given the potential risks of the procedure. This systematic review and meta-analysis aimed to investigate the relative efficacy and safety of DBS in comparison to best medical therapy (BMT) in the treatment of PD. It also aimed to compare the efficacy of DBS between patients with early and advanced PD. A systematic search was performed in Medline, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL). Randomized controlled trials (RCTs) comparing DBS to BMT in PD patients were included. Outcome measures were impairment/disability using the Unified Parkinson's Disease Rating Scale (UPDRS), quality of life (QoL) using the Parkinson's Disease Questionnaire (PDQ-39), levodopa equivalent dose (LED) reduction, and rates of serious adverse events (SAE). Eight eligible RCTs (n = 1,189) were included in the meta-analysis, two of which recruited early PD patients. Regarding efficacy outcomes, there were significant improvements in UPDRS, PDQ-39, and LED scores in favour of DBS (P < 0.00001). There was a significantly greater reduction of LED in patients with early PD (P < 0.00001), but no other differences between early and advanced PD patients were found. The risk of a patient experiencing an SAE was significantly higher in the DBS group (P = 0.005), as was the total number of SAEs (P < 0.00188). Overall, DBS was superior to BMT at improving impairment/disability, QoL, and reducing medication doses, but these benefits need to be weighed against the higher risk of SAEs. There was insufficient evidence to determine the impact of the PD stage on the efficacy of DBS.

Revealing a novel nociceptive network that links the subthalamic nucleus to pain processing

Pain is a prevalent symptom of Parkinson's disease, and is effectively treated by deep brain stimulation of the subthalamic nucleus (STN). However, the link between pain and the STN remains unclear. In the present work, using in vivo electrophysiology in rats, we report that STN neurons exhibit complex tonic and phasic responses to noxious stimuli. We also show that nociception is altered following lesions of the STN, and characterize the role of the superior colliculus and the parabrachial nucleus in the transmission of nociceptive information to the STN, physiologically from both structures and anatomically in the case of the parabrachial nucleus. We show that STN nociceptive responses are abnormal in a rat model of PD, suggesting their dependence on the integrity of the nigrostriatal dopaminergic system. The STN-linked nociceptive network that we reveal is likely to be of considerable clinical importance in neurological diseases involving a dysfunction of the basal ganglia.

Laryngeal Findings in Advanced Parkinson's Disease

Parkinson's disease is a major source of neurologic morbidity. A majority of patients with Parkinson's disease complain of problems with voice, speech, and swallowing. Treatments for these problems center on the improvement of vocal fold adduction through either speech therapy or vocal fold augmentation. No prior study has looked at laryngeal improvement after neurologic surgery, specifically deep brain stimulation, performed to treat Parkinson's disease. The goal of this study was to establish a baseline of laryngeal findings in patients who are considering deep brain stimulation. Fifteen patients underwent physical examination with videostroboscopy and fiberoptic endoscopic evaluation of swallowing before deep brain stimulation. In addition, they were asked to self-report voice handicap. Eighty-seven percent of patients demonstrated significant vocal fold bowing. All patients had some degree of pharyngeal residue of solids noted on evaluation of swallowing. All but one patient had a significant self-reported voice handicap. These findings are reviewed and established as a baseline for further study.

Addiction therapy. Refining deep brain stimulation to emulate optogenetic treatment of synaptic pathology

Circuit remodeling driven by pathological forms of synaptic plasticity underlies several psychiatric diseases, including addiction. Deep brain stimulation (DBS) has been applied to treat a number of neurological and psychiatric conditions, although its effects are transient and mediated by largely unknown mechanisms. Recently, optogenetic protocols that restore normal transmission at identified synapses in mice have provided proof of the idea that cocaine-adaptive behavior can be reversed in vivo. The most efficient protocol relies on the activation of metabotropic glutamate receptors, mGluRs, which depotentiates excitatory synaptic inputs onto dopamine D1 receptor medium-sized spiny neurons and normalizes drug-adaptive behavior. We discovered that acute low-frequency DBS, refined by selective blockade of dopamine D1 receptors, mimics optogenetic mGluR-dependent normalization of synaptic transmission. Consequently, there was a long-lasting abolishment of behavioral sensitization.

Deep brain stimulation does not silence neurons in subthalamic nucleus in Parkinson's patients

Two broad hypotheses have been advanced to explain the clinical efficacy of deep brain stimulation (DBS) in the subthalamic nucleus (STN) for treatment of Parkinson's disease. One is that stimulation inactivates STN neurons, producing a functional lesion. The other is that electrical stimulation activates the STN output, thus "jamming" pathological activity in basal ganglia-corticothalamic circuits. Evidence consistent with both concepts has been adduced from modeling and animal studies, as well as from recordings in patients. However, the stimulation parameters used in many recording studies have not been well matched to those used clinically. In this study, we recorded STN activity in patients with Parkinson's disease during stimulation delivered through a clinical DBS electrode using standard therapeutic stimulus parameters. A microelectrode was used to record the firing of a single STN neuron during DBS (3-5 V, 80-200 Hz, 90- to 200-micros pulses; 33 neurons/11 patients). Firing rate was unchanged during the stimulus trains, and the recorded neurons did not show prolonged (s) changes in firing rate on termination of the stimulation. However, a brief (approximately 1 ms), short-latency (6 ms) postpulse inhibition was seen in 10 of 14 neurons analyzed. A subset of neurons displayed altered firing patterns, with a predominant shift toward random firing. These data do not support the idea that DBS inactivates the STN and are instead more consistent with the hypothesis that this stimulation provides a null signal to basal ganglia-corticothalamic circuitry that has been altered as part of Parkinson's disease.

Bilateral deep brain stimulation vs best medical therapy for patients with advanced Parkinson disease: a randomized controlled trial

CONTEXT

Deep brain stimulation is an accepted treatment for advanced Parkinson disease (PD), although there are few randomized trials comparing treatments, and most studies exclude older patients.

OBJECTIVE

To compare 6-month outcomes for patients with PD who received deep brain stimulation or best medical therapy.

DESIGN, SETTING, AND PATIENTS

Randomized controlled trial of patients who received either deep brain stimulation or best medical therapy, stratified by study site and patient age (< 70 years vs > or = 70 years) at 7 Veterans Affairs and 6 university hospitals between May 2002 and October 2005. A total of 255 patients with PD (Hoehn and Yahr stage > or = 2 while not taking medications) were enrolled; 25% were aged 70 years or older. The final 6-month follow-up visit occurred in May 2006.

INTERVENTION

Bilateral deep brain stimulation of the subthalamic nucleus (n = 60) or globus pallidus (n = 61). Patients receiving best medical therapy (n = 134) were actively managed by movement disorder neurologists.

MAIN OUTCOME MEASURES

The primary outcome was time spent in the "on" state (good motor control with unimpeded motor function) without troubling dyskinesia, using motor diaries. Other outcomes included motor function, quality of life, neurocognitive function, and adverse events.

RESULTS

Patients who received deep brain stimulation gained a mean of 4.6 h/d of on time without troubling dyskinesia compared with 0 h/d for patients who received best medical therapy (between group mean difference, 4.5 h/d [95% CI, 3.7-5.4 h/d]; P < .001). Motor function improved significantly (P < .001) with deep brain stimulation vs best medical therapy, such that 71% of deep brain stimulation patients and 32% of best medical therapy patients experienced clinically meaningful motor function improvements (> or = 5 points). Compared with the best medical therapy group, the deep brain stimulation group experienced significant improvements in the summary measure of quality of life and on 7 of 8 PD quality-of-life scores (P < .001). Neurocognitive testing revealed small decrements in some areas of information processing for patients receiving deep brain stimulation vs best medical therapy. At least 1 serious adverse event occurred in 49 deep brain stimulation patients and 15 best medical therapy patients (P < .001), including 39 adverse events related to the surgical procedure and 1 death secondary to cerebral hemorrhage.

CONCLUSION

In this randomized controlled trial of patients with advanced PD, deep brain stimulation was more effective than best medical therapy in improving on time without troubling dyskinesias, motor function, and quality of life at 6 months, but was associated with an increased risk of serious adverse events.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00056563.

The emerging utility of animal models of chronic neurodegenerative diseases

The two most common neurodegenerative diseases are Alzheimer's disease (AD) and Parkinson's disease (PD). The symptoms are caused by the initially selective degeneration of neuronal subpopulations involved in memory (AD) or movement control (PD). The cause of both diseases is unknown, but ageing is an inevitable risk factor. The identification of disease-associated genes was a breakthrough for the understanding of molecular mechanisms of neurodegeneration and has provided the basis for the establishment of cell culture and animal model systems, instrumental for target validation and drug screening. Familial AD is caused by mutations in the beta-amyloid precursor protein (betaAPP) and in the gene products responsible for its proteolytic processing, namely the presenilins. Transgenic mice expressing these mutant genes develop characteristic AD plaques in an age-dependent manner. A reduction of plaque burden and amelioration of cognitive decline in these animals was recently achieved by vaccination with amyloid beta-protein fibrils. The other hallmark lesion of AD, the neurofibrillary tangle, has been modelled recently in transgenic mice expressing mutant tau protein linked to frontotemporal dementia. PD is characterised by intraneuronal cytoplasmic deposits (Lewy bodies) of the PD-associated gene product alpha-synuclein. Transgenic expression of alpha-synuclein recreated hallmark features of PD in mice and fruit flies, establishing alpha-synuclein as PD-causing drug target. Moreover, environmental risk factors such as the pesticide rotenone have been used successfully to generate rodent models of PD. Lesion models of PD are being exploited for the development of experimental gene therapy and transplantation approaches.

Neurosurgical intervention for Parkinson's disease: an update

For patients with advanced Parkinson's disease who do not respond to levodopa anymore, neurosurgical intervention is the only option. Cell transplantation has not met expectations as yet. Deep brain stimulation is gaining ground and currently seems to be the most efficient, flexible, and safe procedure.

Nerve growth factor prevents 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced cell death via the Akt pathway by suppressing caspase-3-like activity using PC12 cells: relevance to therapeutical application for Parkinson's disease

Nerve growth factor (NGF) mediates a variety of nerve cell actions through receptor tyrosine kinase TrkA. It has been revealed that the Akt pathway contributes to the prevention of apoptosis. It is thought that Parkinson's disease involves apoptosis, and NGF prevents apoptosis in an in vivo model system. However, there is no evidence that the Akt pathway helps to prevent parkinsonism. Here, we report that NGF prevents apoptosis induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in PC12 cells as an in vitro model system of parkinsonism and that this survival effect diminishes on addition of LY294002, a specific inhibitor of phosphatidylinositol 3-kinase. Immunocytochemical analysis revealed that 1 mM MPTP-treated cells or dominant negative Akt-expressing cells, to which were added NGF and MPTP, undergo apoptosis. Moreover, the caspase-3-like activity is increased by addition of MPTP or MPTP with NGF and LY294002. The importance of another signal pathway is shown by PD98059, a specific inhibitor of MAP kinase (MAPK) kinase, but PD98059 does not alter the survival effect in this model system. These results indicate that the Akt pathway helps to prevent parkinsonism by suppressing caspase-3-like activity, but the MAPK pathway is not involved in the NGF-dependent survival enhancing effect in this model system.