Role of surgery in the treatment of motor complications

Update on deep brain stimulation in Parkinson's disease

Deep brain stimulation (DBS) is considered a safe and well tolerated surgical procedure to alleviate Parkinson’s disease (PD) and other movement disorders symptoms along with some psychiatric conditions. Over the last few decades DBS has been shown to provide remarkable therapeutic effect on carefully selected patients. Although its precise mechanism of action is still unknown, DBS improves motor functions and therefore quality of life. To date, two main targets have emerged in PD patients: the globus pallidus pars interna and the subthalamic nucleus. Two other targets, the ventralis intermedius and zona incerta have also been selectively used, especially in tremor-dominant PD patients. The main indications for PD DBS have traditionally been motor fluctuations, debilitating medication induced dyskinesias, unpredictable “off time” state, and medication refractory tremor. Medication refractory tremor and intolerable dyskinesia are potential palliative indications. Besides aforementioned targets, the brainstem pedunculopontine nucleus (PPN) is under investigation for the treatment of ON-state freezing of gait and postural instability. In this article, we will review the most recent literature on DBS therapy for PD, including cutting-edge advances and data supporting the role of DBS in advanced neural-network modulation.

Facing the unique challenges of dyskinesias in Parkinson’s disease

Dyskinesia is among the most challenging complications of levodopa and dopaminergic drug therapy in advanced Parkinson’s disease. This symptom has a negative impact on the quality of life of patients with Parkinson’s disease and is hard to manage. Current advances in our understanding of the diverse phenomenology and complicated pathophysiology of dyskinesia have led to a number of novel strategies aimed at better control of this complication. Further insight has been gained from focusing on the characteristics of the rating scale used for assessment of dyskinesia and from the inherent susceptibility of dyskinesia to placebo effect. Here, we will briefly review the phenomenology, pathophysiology and the treatment of dyskinesia in Parkinson’s disease.

Propofol decreases neuronal population spiking activity in the subthalamic nucleus of Parkinsonian patients

BACKGROUND

Implantation of deep brain stimulation (DBS) electrodes in the subthalamic nucleus (STN) for the treatment of Parkinson disease is often performed using microelectrode recording (MER) of STN population spike activity. The extent to which sedative drugs interfere with MER is unknown. We recorded the population activity of STN neurons during propofol sedation and examined its effect on neuronal activity.

METHODS

The procedure was performed during DBS surgery for Parkinson disease. We administered propofol (50 μg/kg/min) at a constant electrode location in the STN until stable sedation was achieved. We recorded the electrical activity, and calculated its root mean square (RMS) before, during, and after the propofol infusions.

RESULTS

The activity of 24 electrode trajectories was recorded in 16 patients. The RMS of STN activity decreased significantly after propofol administration in 18 of the 24 trajectories. The average normalized RMS decreased by 23.2%± 9.1% (mean ± SD) during propofol administration (P < 0.001), and returned to baseline 9.3 ± 4.0 minutes after it was stopped.

CONCLUSIONS

Propofol administration leads to a significant decrease of STN neuronal activity. Thus, it may interfere with MER identification of the STN borders. However, activity returns to baseline shortly after administration stops. Therefore, propofol can be safely used until shortly before MER for DBS.

Medical treatment of Parkinson disease

The cardinal characteristics of Parkinson disease (PD) include resting tremor, rigidity, and bradykinesia. Patients may also develop autonomic dysfunction, cognitive changes, psychiatric symptoms, sensory complaints, and sleep disturbances. The treatment of motor and non-motor symptoms of Parkinson disease is addressed in this article.

Over-expression of the potassium channel Kir2.3 using the dopamine-1 receptor promoter selectively inhibits striatal neurons

Dysfunction of basal ganglia circuits underlies a variety of movement disorders and neuropsychiatric conditions. Selective control of the electrical activity of striatal outflow pathways by manipulation of ion channel function presents a novel therapeutic approach. Toward this end, we have constructed and studied in vitro an adenoviral gene transfer vector that employs the promoter region of the dopamine-1 receptor to drive expression of the inward rectifier K(+) channel Kir2.3. The use of this neuronal promoter confers cell-type specificity and a physiological level of trans-gene expression in rat primary striatal cultures. The electrophysiological properties were confirmed in transfected human embryonic kidney cells, in which an inwardly-rectifying, Cs(+)-sensitive current was measured by voltage clamp. Current clamp studies of transduced striatal neurons demonstrated an increase in the firing threshold, latency to first action potential and decrease in neuronal excitability. Neurotoxin-induced activation of c-Fos, a marker of neuronal activity, was blocked in transduced neurons indicating that the decrease in electrical excitability was physiologically significant. When used in vivo, this strategy may have the potential to positively impact movement disorders by selectively changing activity of neurons belonging to the direct striatal pathway, characterized by the expression of dopamine-1 receptors.

Levodopa-induced dyskinesias

Levodopa-induced dyskinesias (LID) are common and difficult to treat. This review focuses on three issues related to LID: clinical features, classification and rating, pathophysiology and pathogenesis, and management. The three primary clinical syndromes are OFF-period dystonia, peak-dose dyskinesia, and diphasic dyskinesia. Several other forms also occur, making the evaluation and choice of treatment complicated. A core component of the pathophysiology of LID is overactivity of the direct striatal output pathway. This pathway provides a direct GABAergic connection by which the striatum inhibits the output regions of the basal ganglia, i.e., the internal globus pallidus and the substantia nigra pars reticulata. Altering dopaminergic dosing and timing can abate dyskinesias, but usually impact the control of parkinsonism. Putative therapies to reduce the problem of dyskinesias could focus on the glutamatergic, GABAergic, alpha2 adrenergic, serotonergic (5HT1A, 5HT2A), opioid, histamine H3, adenosine A2A receptors, the monoamine transport or cannabinoid CB1 receptors systems. The only currently available drug with an evidence-based recommendation on efficacy for dyskinesia is amantadine. Therapy goals include the prevention of dyskinesia and treatment of dyskinesias that are troublesome clinically. New rating measures to assess severity and disability related to dyskinesia are in the process of development and clinimetric testing.

Levodopa-induced Dyskinesia in Parkinson’s disease: Epidemiology, etiology, and treatment

Although levodopa is the gold standard for treating motor symptoms of Parkinson's disease (PD), long-term therapy leads to levodopa-induced dyskinesia (LID). Dyskinesia refers to involuntary movements other than tremor and most commonly consists of chorea that occurs when levodopa-derived dopamine is peaking in the brain ("peak-dose dyskinesia"). However, dyskinesia can also consist of dystonia or myoclonus and occur during other parts of the levodopa dosing cycle. New validated rating scales and home diaries can better help the health care provider assess the timing and severity of dyskinesia. The exact etiology of LID is unknown, but there is evidence that abnormal pulsatile stimulation of dopamine receptors may be contributory. Treatment of LID includes adjustment of PD medications to maximize "on" time without troublesome dyskinesia. Amantadine is the only medication available with demonstrated ability to reduce the expression of established LID without reducing antiparkinsonian benefit. Other medications that are currently being studied to treat established LID include antiepileptics and serotonergic medications. Deep brain stimulation of the subthalamic nucleus is now the most commonly used surgical procedure for PD patients, and it is very effective in treating LID.

Unilateral deep brain stimulation of the subthalamic nucleus for Parkinson disease

OBJECT

The object of this study was to assess the results of unilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) for management of advanced Parkinson disease (PD).

METHODS

A clinical series of 24 patients (mean age 71 years, range 56-80 years) with medically intractable PD, who were undergoing unilateral magnetic resonance imaging-targeted, electrophysiologically guided STN DBS, completed a battery of qualitative and quantitative outcome measures preoperatively (baseline) and postoperatively, using a modified Core Assessment Program for Intracerebral Transplantations protocol. The mean follow-up period was 9 months. Statistically significant improvement was observed in the Unified Parkinson's Disease Rating Scale (UPDRS) Part II score (18%), the total UPDRS PART III score (31%), the contralateral UPDRS Part III score (63%), and scores for axial motor features (19%), contralateral tremor (88%), rigidity (60%), bradykinesia (54%), and dyskinesia (69%), as well as the Parkinson's Disease Quality of Life questionnaire score (15%) in the on-stimulation state compared with baseline. Ipsilateral symptoms improved by approximately 15% or less. Performance on the Purdue pegboard test improved in the contralateral hand in the on-stimulation state compared with the off-stimulation state (38%, p < 0.05). The daily levodopa-equivalent dose was reduced by 21% (p = 0.018). Neuropsychological tests revealed an improvement in mental flexibility and a trend toward reduced letter fluency. There were no permanent surgical complications. Of the 16 participants with symmetrical disease, five required implantation of the DBS unit on the second side.

CONCLUSIONS

Unilateral STN DBS is an effective and safe treatment for selected patients with advanced PD. Unilateral STN DBS provides improvement of contralateral motor symptoms of PD as well as quality of life, reduces requirements for medication, and possibly enhances mental flexibility. This method of surgical treatment may be associated with a reduced risk and may provide an alternative to bilateral STN DBS for PD, especially in older patients or patients with asymmetry of parkinsonism.

Treatment of levodopa-induced dyskinesia

Levodopa provides the most effective symptomatic treatment for Parkinson's disease (PD). Initiation of treatment of PD too early and/or very aggressive treatment with large doses of levodopa results in severe motor fluctuations and dyskinesias in 30% of patients with PD. Chronic levodopa treatment over a period of 9 years or more will invariably result in disabling motor fluctuations in 90% of PD patients. The motor fluctuations and associated dyskinesia are due to progressive dopamine denervation, an unregulated pattern of release of dopamine in the synapse, fluctuating levels of receptor sensitivity, and fluctuating levels of dopamine receptor stimulation. Once the dyskinesias are established, they are difficult to treat. The current medical therapy is a by-product of several explorative open-label trials, as well as a few blinded and double-label placebo-controlled clinical trials, of varying duration in a small number of patients. These studies suggest that amantadine, a glutamate antagonist, may be the most effective, easily available, and inexpensive medical treatment for levodopa-induced dyskinesia. Several other drugs, already approved for other medical ailments, also have been tried but not evaluated in large-scale clinical trials. None of these drugs is approved by the US Food and Drug Administration specifically for levodopa-induced dyskinesia. By far, the most effective treatment of levodopa-induced dyskinesia appears to be deep brain stimulation, with globus pallidus interna or the subthalamic nucleus as the two major targets of placement of electrodes.

Review of the therapeutic management of Parkinson's disease. Report of a joint task force of the European Federation of Neurological Societies (EFNS) and the Movement Disorder Society-European Section (MDS-ES). Part II: late (complicated) Parkinson's disease

To provide evidence-based recommendations for the management of late (complicated) Parkinson's disease (PD), based on a review of the literature. Complicated PD refers to patients suffering from the classical motor syndrome of PD along with other motor or non-motor complications, either disease-related (e.g. freezing) or treatment-related (e.g. dyskinesias or hallucinations). MEDLINE, Cochrane Library and INAHTA database literature searches were conducted. National guidelines were requested from all EFNS societies. Non-European guidelines were searched for using MEDLINE. Part II of the guidelines deals with treatment of motor and neuropsychiatric complications and autonomic disturbances. For each topic, a list of therapeutic interventions is provided, including classification of evidence. Following this, recommendations for management are given, alongside ratings of efficacy. Classifications of evidence and ratings of efficacy are made according to EFNS guidance. In cases where there is insufficient scientific evidence, a consensus statement ('good practice point') is made.

Post- versus presynaptic plasticity in L-DOPA-induced dyskinesia

L-3,4-dihydroxyphenylalanine (L-DOPA) remains the most efficacious drug for the treatment of Parkinson's disease (PD), but causes adverse effects that limit its utility. L-DOPA-induced dyskinesia (abnormal involuntary movements) is a significant clinical problem that attracts growing scientific interest. Current notions attribute the development of dyskinesia to two main factors, viz. the loss of nigrostriatal dopamine (DA) projections and the maladaptive changes produced by L-DOPA at sites postsynaptic to the nigrostriatal neuron. Basic research in the past 15 years has placed a lot of emphasis on the postsynaptic plasticity associated with dyskinesia, but recent experimental work shows that also some presynaptic factors, involving the regulation of L-DOPA/DA release and metabolism in the brain, may show plasticity during treatment. This review summarizes significant studies of L-DOPA-induced dyskinesia in patients and animal models, and outlines directions for future experiments addressing mechanisms of presynaptic plasticity. These investigations may uncover clues to the varying susceptibility to L-DOPA-induced dyskinesia among PD patients, paving the way for tailor-made treatments.