Efficacy and safety of stereotaxic surgical treatment of tremor disorders

Surgical approaches to treatment of Parkinson's disease: Implications for speech function

Although neurosurgical procedures have been reported to be successful in relieving many of the motor symptoms of Parkinson's disease (PD) (e.g., tremor, rigidity, bradykinesia) in the limb musculature, their effect on speech is much less consistent. This paper will review and evaluate reports in the literature on the effects of various surgical interventions for PD, including thalamotomy, pallidotomy, and DBS, on speech. In particular the paper will focus on the implications of these findings for one's understanding of the neurological control of the speech mechanism. As a foundation, contemporary models of the neuropathophysiology of PD and hypokinetic dysarthria will be outlined and explained. The various neurosurgical treatments for PD will be described and their theoretical underpinning discussed with regard to their proposed effects on subcortical and cortical motor control systems. Evidence suggestive of the need to reconsider contemporary thinking in relation to the neurology of speech and the need to differentiate it from limb neurology will be highlighted.

Neuropsychiatric complications of medical and surgical therapies for Parkinson's disease

This review deals with the range of neuropsychiatric problems that may arise from the use of medical and surgical therapies in the treatment of Parkinson's disease. As new approaches emerge, these problems are diversifying. Well-recognized drug-related complications include hallucinations and psychosis and the so-called dopamine-dysregulation syndrome. The etiology of these problems has not been fully established and is not clearly dose related, while the management can be difficult and needs to be tailored to the individual patient. Cholinergic and dopaminergic drugs may both influence cognitive function. The development of pharmacogenetics could improve the therapeutic ratio of medical approaches to PD in the future. The literature relating to the neuropsychiatric issues complicating the surgical treatment of Parkinson's disease is more recent and frequently suffers from methodological problems, lack of a systematic approach, and adequate patient follow-up. The emergence of neuropsychiatric problems in association with surgery has shed new light upon the pathophysiological mechanisms underpinning these symptoms. Depression, hypomania, euphoria, mirth, and hypersexuality have all been described following deep brain stimulation procedures, although most studies have concentrated upon the depressive features. Anxiety has been described only rarely to date. Fortunately, permanent cognitive complications appear to be rare. The optimal management approach for surgically related neuropsychiatric problems is unknown at present. Prospective multicenter studies would contribute significantly to resolving this therapeutic uncertainty.

Management of essential tremor

Essential tremor (ET) is the most prevalent tremor syndrome. It commonly affects the hands, head, voice, and other body parts. Appropriate management begins with correct diagnosis. Primidone and propranolol are the first-line medications for the treatment for ET, but several other medications may also provide benefit. In patients with medically refractory tremor, alternative therapies, including surgery or injections of botulinum toxin, may be considered.

Early Parkinson's disease: what is the best approach to treatment

Early and correct diagnosis and treatment of Parkinson's disease (PD) are crucial for the patient's well being. At the first visit, it is important to deal with the patient's misconceptions of the disease and its course, to offer sources of information and to suggest exercises. To make a correct initial diagnosis of PD we need to assess the course of the initial levodopa responsiveness. The most frequent challenges in diagnosing PD are the conditions of essential tremor and multiple system atrophy. PD has 3 stages of development: (i) early--from the onset of symptoms to the appearance of motor fluctuations; (ii) middle--from motor fluctuations to the appearance of moderate-to-severe disability; and (iii) advanced--when moderate-to-severe disability is present. The medical treatment of early PD should be started when functional disability appears, which is a different threshold for each patient. For patients below 65 years old, or above 65 years old but with preserved mental function and with no severe comorbidity, initial monotherapy with a dopamine agonist is advisable. This approach appears to delay the appearance and reduce the amount of late motor complications with subsequent levodopa treatment. All dopamine agonists have similar efficacy, which is less than that of levodopa. It is important to consider the adverse effect profile when a choice for initial or adjunctive therapy is made. When levodopa therapy is started as an adjunct in younger patients or as initial monotherapy in older patients, sustained-release levodopa preparations are preferred. They have a longer half-life and possibly stimulate the dopamine receptors more continuously. Anticholinergic drugs are appropriate for younger patients with tremor-dominant PD. Amantadine is mainly used for dyskinesia control. Catechol-O-methyl-transferase inhibitors and neurosurgery are not treatments of choice for early PD but can be very effective for more advanced disease. The presence of presymptomatic markers of PD, such as changes in odour detection, handwriting, speech, movement time of self-initiated motor acts, personality traits, presence of antibodies against dopaminergic neurons, pattern of positron emission tomography results, appearance of mitochondrial DNA mutation profiles, etc., appear to be very important in the light of the emerging neuroprotective therapies. Neuroprotection is aimed at slowing the rate of disease progression. Selegiline has been shown to cause a mild delay in the need for levodopa, possibly suggesting some protection. However, this initial benefit was not sustained in long term studies. Currently, there is no neuroprotective drug for PD.

Coherence between low-frequency activation of the motor cortex and tremor in patients with essential tremor

BACKGROUND

In healthy people, rhythmic activation of the motor cortex in the 15-30 Hz frequency range accompanies and contributes to voluntarily-generated postural contractions of contralateral muscle. In patients with Parkinson's disease, an abnormal low-frequency activation of the motor areas of the cortex occurs and has been directly linked to the characteristic 3-6 Hz rest tremor of this disease. We therefore investigated whether the motor cortex is involved in the transmission of the rhythmic motor drive responsible for generating essential tremor.

METHODS

Non-invasive recordings of activity from the hand area of the motor cortex were made from six patients with essential tremor by magnetoencephalography. The recordings were made simultaneously with the electromyogram recorded from contralateral finger muscles during periods of postural tremor. A statistical spectral analysis was done to determine at which frequencies the two signals were correlated.

FINDINGS

Spectral analysis of the electromyogram signals showed a significant low-frequency component at the frequency of the tremor bursts. However, there was no coherence between magnetoencephalogram and electromyogram recordings at the tremor frequency, indicating that no correlation existed between the tremor signal and low-frequency activity recorded from the primary motor cortex in individuals with essential tremor. Coherence at frequencies higher than the tremor frequency was similar to that in healthy individuals performing voluntary postural contractions.

INTERPRETATION

The absence of significant coherence between the magnetoencephalogram and electromyogram at tremor frequencies suggests that in essential tremor the tremor is imposed on the active muscle through descending pathways other than those originating in the primary motor cortex. These findings challenge the model widely used to explain the efficacy of neurosurgical treatment of essential tremor, are in contrast to those of previous studies of parkinsonian rest tremor, and highlight an important difference in the pathophysiology of essential and parkinsonian tremor.

Cognitive outcomes after deep brain stimulation for Parkinson's disease: a review of initial studies and recommendations for future research

Modern ablative surgery for movement disorders probably results in less frequent and severe cognitive morbidity than seen in early surgical series. Nonetheless, recent studies indicate that neurobehavioral functions commonly compromised in Parkinson's disease (PD) (e.g., executive functions, verbal fluency, and memory) are negatively impacted in some patients by lesion placement. The potential reversibility of cognitive dysfunction after chronic electrical deep brain stimulation (DBS) for PD has lead some to favor this treatment modality over ablation. This paper reviews the initial studies of the cognitive effects of thalamic, pallidal, and subthalamic DBS. These studies suggest that DBS is relatively safe from a cognitive standpoint and that the benefits of motor improvements probably outweigh the cost of minimal cognitive morbidity. This conclusion must be offered with caution, however, given the small numbers of studies to date and their methodological limitations. Neurobehavioral research has yet to adequately address (1) outcome relative to appropriate control groups; (2) effects of electrode placement versus stimulation; (3) laterality- and site-specific effects of DBS; (4) long-term effects of DBS; (5) effects of stimulation parameters; (6) risk factors for cognitive dysfunction with DBS; (7) whether cognitive dysfunction associated with DBS is reversible; and (8) comparative neurobehavioral outcome after DBS and ablation. DBS affords an exciting opportunity to clarify the neurobehavioral role of the basal ganglia.

Thalamic, subthalamic nucleus and internal pallidum stimulation in Parkinson's disease

The limits of drug therapy in severe forms of Parkinson's disease have lead to a renewal of functional neurosurgery of the basal ganglia and the thalamus. Deep brain stimulation (DBS) of these structures was developed with the aims of reducing the morbidity of surgery and of offering an adaptative treatment. DBS was first applied to the thalamus in patients with severe tremor. Tremor of the hemibody is greatly reduced by stimulation of the contralateral electrode in 85% of the cases. There is little change in other symptoms. However, motor fluctuations and dyskinesias are a more frequent problem than severe tremor; in attempt to treat these symptoms, DBS has recently been applied to the subthalamic nucleus (STN) and the internal pallidum (GPi). STN stimulation greatly decreases off motor symptoms and motor fluctuations, which allows a reduction of drug dosage and consequently of dyskinesias. GPi stimulation decreases dyskinesias in most patients, but the effect on off motor symptoms is more variable from one series to another, from very good to nil. The severe morbidity of DBS applied to these 3 targets is low. Comparative studies of the cost and the efficacy of DBS and lesions applied to these different targets are now required.

Thalamic surgery and tremor

The results of thalamotomy for the various kinds of tremor are described. The nomenclature of the ventrolateral thalamic nuclei is discussed. Long-term thalamic stimulation seems a promising addition to or alternative for the thalamotomy, but this has still to be proven by a prospective trial that includes a cost-effectiveness analysis.

Chronic electrical stimulation of the left ventrointermediate (Vim) thalamic nucleus for the treatment of pharmacotherapy-resistant Parkinson's disease: a differential impact on access to semantic and episodic memory?

Thalamotomy for medically refractory Parkinson's disease (PD) is considered to be efficacious and relatively safe. Because a minority of patients experience decrements in language and memory (often mild and transient) after thalamotomy, chronic thalamic deep brain stimulation (DBS) might be a safer treatment given its reversibility and the modifiability of stimulation parameters. Two preliminary studies support the relative cognitive safety of unilateral DBS of the ventral intermediate (Vim) thalamic nucleus, but it is unclear whether possibly subtle changes in language and memory represent effects of "microthalamotomy" or of stimulation per se. This report provides preliminary data concerning effects of left thalamic stimulation on information processing speed, semantic memory (verbal fluency and visual confrontation naming), and verbal episodic memory in a patient with PD. In addition to being evaluated before and 3 and 6 months after surgery, the patient was tested 18 months after surgery either on or off medications and with the stimulator turned either on or off (order counterbalanced across medication conditions). Test performance differences between the stimulation conditions were attenuated "off" as compared to "on" medication. Vim stimulation consistently, albeit subtly, improved semantic verbal fluency but interfered with immediate recall of word lists. Parallels to findings from acute, intraoperative thalamic stimulation studies are explored. The hypothesis is offered that left Vim stimulation might facilitate access to semantic memory, but interfere with episodic memory processes.

Neuropsychological functioning before and after unilateral thalamic stimulating electrode implantation in Parkinson's disease

One theoretical advantage of chronic thalamic stimulation compared with thalamotomy for the treatment of refractory Parkinson's disease (PD) entails the avoidance and reversibility of potential cognitive morbidity. Support for the cognitive safety of thalamic stimulation remains largely anecdotal; empirical data are limited to the neuropsychological findings published for one small series of patients. The purpose of this study was to supplement those published findings that pertain to the mean changes in neuropsychological test scores and to extend previous findings by evaluating cognitive changes in individual cases from preoperative baseline to 4 months after electrode implantation. Nine patients with tremor-dominant, refractory PD underwent unilateral implantation of a deep brain stimulating electrode in the ventralis intermedius thalamic nucleus (five patients on their left and four patients on their right sides). A neuropsychological test battery was administered to each patient to evaluate attention, language, memory, and visuoperceptual and executive functions during their best “on” state before surgery, while on a medication regimen, and with the stimulator turned on after surgery. As a group, the patients attained significantly higher scores on word list recognition (discriminability) and delayed recall of prose passages after surgery than before surgery. In addition, there was a trend toward higher scores on a visual confrontation naming test after surgery. Examination of individual patient data indicated gains and losses in test scores exceeding two standard deviations to be very rare. Changes of one standard deviation were also relatively rare, but gains were more likely to occur than losses. These observations provide preliminary support for the cognitive safety of thalamic stimulation for PD.