Electrical stimulation of the subthalamic nucleus in advanced Parkinson's disease

BACKGROUND

In many patients with idiopathic Parkinson's disease, treatment with levodopa is complicated by fluctuations between an "off" period, when the medication is not working and the motor symptoms of parkinsonism are present, and an "on" period, when the medication is causing improved mobility, often accompanied by debilitating dyskinesias. In animal models of Parkinson's disease, there is overactivity in the subthalamic nucleus, and electrical stimulation of the subthalamic nucleus improves parkinsonism. We therefore sought to determine the efficacy and safety of electrical stimulation of the subthalamic nucleus in patients with Parkinson's disease.

METHODS

We studied 24 patients with idiopathic Parkinson's disease in whom electrodes were implanted bilaterally in the subthalamic nucleus under stereotactic guidance with imaging and electrophysiologic testing of the location. Twenty were followed for at least 12 months. Clinical evaluations included the Unified Parkinson's Disease Rating Scale, a dyskinesia scale, and timed tests conducted before and after surgery, when patients were off and on medications.

RESULTS

After one year of electrical stimulation of the subthalamic nucleus, the patients' scores for activities of daily living and motor examination scores (Unified Parkinson's Disease Rating Scale parts II and III, respectively) off medication improved by 60 percent (P<0.001). The subscores improved for limb akinesia, rigidity, tremor, and gait. In the testing done on medication, the scores on part III improved by 10 percent (P<0.005). The mean dose of dopaminergic drugs was reduced by half. The cognitive-performance scores remained unchanged, but one patient had paralysis and aphasia after an intracerebral hematoma during the implantation procedure.

CONCLUSIONS

Electrical stimulation of the subthalamic nucleus is an effective treatment for advanced Parkinson's disease. The severity of symptoms off medication decreases, and the dose of levodopa can be reduced with consequent reduction in dyskinesias.

Effect of parkinsonian signs and symptoms of bilateral subthalamic nucleus stimulation

In monkeys rendered parkinsonian, lesions and electrical stimulation of the subthalamic nucleus reduce all major motor disturbances. The effect of electrical stimulation of the subthalamic nucleus was assessed in three patients with disabling akinetic-rigid Parkinson's disease and severe motor fluctuations. Quadripolar electrodes connected to a pulse generator were implanted in the subthalamic nuclei on both sides. Patients were evaluated with the unified Parkinson's disease rating scale and timed motor tests. 3 months after surgery, activities of daily living scores had improved by 58-88% and motor scores by 42-84%. This improvement was maintained for up to 8 months in the first patient operated upon. One patient was confused for 2 weeks after surgery, and another developed neuropsychological impairment related to a thalamic infarction which improved over 3 months. In one patient, stimulation could induce ballism that was stopped by reduction of stimulation. This is the first demonstration in human beings of the part played by the subthalamic nuclei in the pathophysiology of Parkinson's disease.

Bilateral subthalamic nucleus stimulation for severe Parkinson's disease

Subthalamic nucleus (STN) lesions or high-frequency stimulations could improve parkinsonian symptoms in monkeys treated by MPTP. We have applied the procedure of chronic stimulation to the STN in severely disabled parkinsonian patients. This article presents the case of the first patient operated on bilaterally. Bilateral STN stimulation has greatly improved akinesia and rigidity. The benefit was maintained < or = 15 months after surgery. Unilateral stimulation induced motor effects mainly in contralateral limbs. Further studies are needed to evaluate the value of this procedure in the treatment of Parkinson's disease.

Treatment of tremor in Parkinson's disease by subthalamic nucleus stimulation

The recent resurgent interest in functional surgery for the treatment of Parkinson's disease (PD) has focused on the effects on akinesia and levodopa-induced dyskinesia. Stimulation of the subthalamic nucleus (STN) improves akinesia and rigidity but its effects on tremor have not been studied. The objective of this study was to assess the efficacy of STN stimulation on tremor in patients with the complete parkinsonian triad with motor fluctuations. Of 27 consecutive patients with STN stimulation (26 bilateral), 15 exhibited tremor rated at least 2/4 according to item 20 (rest tremor) of the Unified Parkinson's Disease Rating Scale (UPDRS) in at least one limb. The mean preoperative tremor score was 11.3+/-5.6 in off-drug and 1.2+/-2.4 in on-drug conditions. The postoperative tremor scores at the last follow up (from 1-12 months) were 2.2+/-2.2 off-drug/on-stimulation and 0.2+/-0.4 on-drug/on-stimulation. Both rest and action tremors were improved in all patients. The UPDRS tremor score was reduced by 80%, rigidity score by 65%, and akinesia score by 51% on average. For the three symptoms, the stimulation effect was close to that induced before surgery by a suprathreshold dose of levodopa given in the morning. STN stimulation can be considered an interesting alternative to thalamic or internal pallidal surgery even in PD patients with severe high-amplitude tremor. In keeping with electrophysiological data in monkeys rendered parkinsonian by MPTP injections, our results emphasize the importance of the oscillation of a neuronal loop involving the STN in the pathophysiology of parkinsonian tremor.

Loss of thalamic intralaminar nuclei in progressive supranuclear palsy and Parkinson's disease: clinical and therapeutic implications

Whilst many reports mention neurofibrillary tangle pathology in the thalamus in progressive supranuclear palsy, there has been little detailed regional analysis of the distribution and density of thalamic pathology in this disease or in other parkinsonian syndromes. The caudal intralaminar thalamic nuclei are the major thalamic regulators of the caudate nucleus and putamen, areas known to be dysfunctional in progressive supranuclear palsy and Parkinson's disease. We investigated whether these thalamic nuclei degenerate in patients with these disorders compared with age-matched, neurologically normal controls. Neurofibrillary tangle and Lewy body pathology was assessed and unbiased optical disector methods were used to quantify total neuronal number. Despite different thalamic pathology, there was a dramatic reduction in the total neuronal number in the caudal intralaminar nuclei in both progressive supranuclear palsy and Parkinson's disease (40-55% loss). In contrast, there was no loss of volume or total neuronal number in the limbic thalamic nuclei in either disease group, indicating selective degeneration of the caudal intralaminar nuclei. In Parkinson's disease, Lewy bodies were found in these regions, while in progressive supranuclear palsy abundant intracellular neurofibrillary tangles and glial tangles concentrated in the caudal intralaminar nuclei. However, tangle formation accounted for only a small proportion of cell loss (</=10%) in the thalamus in progressive supranuclear palsy. These findings have several implications. The caudal intralaminar thalamus appears to be one of three basal ganglia sites commonly affected in both progressive supranuclear palsy and Parkinson's disease. These sites are the dopaminergic substantia nigra, the cholinergic pedunculopontine tegmental nucleus and, from our results, the glutamatergic caudal intralaminar thalamus. In both diseases these sites contain characteristic but different pathologies, indicating disease-specific mechanisms of neurodegeneration. Interestingly, the proportion of remaining neurons affected by these pathologies is low. This may indicate additional (possibly common) cellular mechanisms responsible for the degeneration in these regions. Both the dopaminergic nigra and the glutamatergic caudal intralaminar thalamus are the major regulators of basal ganglia function via the caudate nucleus and putamen. The pedunculopontine tegmental nucleus has major projections to both of these regulators. These findings indicate that dysregulation of two neurotransmitter systems within the basal ganglia may underlie common parkinsonian symptoms in these disorders. For patients with Parkinson's disease, this loss of glutamate regulation may help explain some problems with dopamine replacement therapies, particularly over time. For patients with progressive supranuclear palsy, more widespread degeneration of basal ganglia structures would contribute to poor treatment outcomes.

Thalamic stimulation for neuropathic pain

Eighteen patients with neuropathic pain underwent thalamic electrode implantation. Satisfactory initial pain relief ensued in 14, and their electrode systems were internalized for long-term use. Twelve of the 14 continue to obtain either complete or partial pain relief by regular stimulation. One of the other two patients has had a complete remission of pain, apparently spontaneously, and the other had to have the electrodes removed after it retracted from his thalamus on two occasions. The electrodes have been placed in the sensory nucleus of the thalamus where stimulation evokes paresthesias in the painful part of the body. Technical problems consisting of our inability to locate the target in two patients and our failure to fix the electrode adequately in one prevented us from employing the treatment in three patients. The fourth patient had temperature dysesthesia which was not altered during 2 weeks of stimulation.

Diencephalic amnesia: a reappraisal

The anatomical basis of memory disorder related to lesions of the diencephalon is a controversial matter. A study of a patient who developed severe amnesia in association with bilateral metastatic tumour invasion of the medial and posterior thalamus is reported. The findings in this case have led to further discussion of this unsettled issue.

Deep brain stimulation for severe, chronic pain

Deep brain electrodes placed in the parafascicularis-centre-median area (pf-CM) can reliably relieve severe chronic pain of long duration by simple electrical stimulation, in selected cases. Twenty-eight patients are presented here who had one or more electrodes placed for periods ranging from a few days to several months. Overall results rated good-to-excellent (having 50% or more relief of the prestimulation pain) were seen in 76% of the cases. Intraoperative test stimulation has been very useful in predicting future effectiveness. Also presented are a new disposable ventricular catheter and a burr hole plug and cap for anchoring the electrode wires in the skull.

The current status of analgesic brain stimulation

This paper reviews the author's nine years of experience in analgesic brain stimulation. During this time, of 22 patients with pain of peripheral origin who were treated with periaqueductal gray (PAG), stimulation 16 achieved successful control of pain. Of 40 patients who presented with deafferentation pain, 16 were able to control their dysesthesia by brain stimulation of the subcortical somatosensory region alone; follow-up was over a long period. The mechanism of deafferentation pain is poorly understood and the effectiveness of subcortical somatosensory electrical stimulation to relieve such pain is based on empirical observation. The analgesia produced by PAG stimulation appears to be mediated by the release of beta-endorphin from the anterior hypothalamus. The released beta-endorphin binds to the opiate receptors in the PAG and activates the descending pain-inhibitory pathway. However, the repetitive stimulation of this serotonergic system produces tolerance to its analgesic effect, due to a decreased rate of serotonin turnover. Loading of the serotonin precursor by dietary supplementation of the essential amino acid L-tryptophan reverses this tolerance.

Chronic electrical stimulation of the thalamic unspecific activating system in a patient with coma due to midbrain and upper brain stem infarction

Chronic intermittent bipolar electrical stimulation of the left nucleus reticulatus polaris thalami was performed in a patient in a state of subcoma due to ischaemic infarction of wide medial parts of the midbrain, mainly the tegmentum, and the right-sided mediobasal parts of the forebrain. Stimulation immediately resulted in autonomic reactions and behavioural arousal reactions during the periods of stimulation. Longterm effect consisted of a rise in the level of clinical responsiveness for a period of seven weeks. A preexistent severe pneumonia disappeared completely after one week of stimulation and returned after seven weeks. The results are discussed on the basis of the pathoanatomical findings and of the physiological functions of the damaged as well as of the stimulated areas.

Burst discharges in neurons of the thalamic reticular nucleus are shaped by calcium-induced calcium release

The nucleus reticularis thalami (NRT) is a layer of inhibitory neurons that surrounds the dorsal thalamus. It appears to be the 'pacemaker' of certain forms of slow oscillations in the thalamus and was proposed to be a key determinant of the internal attentional searchlight as well as the origin of hypersynchronous activity during absence seizures. Neurons of the NRT exhibit a transient depolarization termed low threshold spike (LTS) following sustained hyperpolarization. This is caused by the activation of low-voltage-activated Ca2+ channels (LVACC). Although the role of these channels in thalamocortical oscillations was studied in great detail, little is known about the downstream intracellular Ca2+ signalling pathways and their feedback onto the oscillations. A signalling triad consisting of the sarco(endo)plasmic reticulum calcium ATPase (SERCA), Ca2+ activated K+ channels (SK2), and LVACC is active in dendrites of NRT neurons and shapes rhythmic oscillations. The aim of our study was to find out (i) if and how Ca2+-induced Ca2+ release (CICR) via ryanodine receptors (RyR) can be evoked in NRT neurons and (ii) how the released Ca2+ affects burst activity. Combining electrophysiological, immunohistochemical, and two-photon Ca2+ imaging techniques, we show that CICR in NRT neurons takes place by a cell-type specific coupling of LVACC and RyR. CICR could be evoked by the application of caffeine, by activation of LVACC, or by repetitive LTS generation. During the latter, CICR contributed 30% to the resulting build-up of [Ca2+]i. CICR was abolished by cyclopiazonic acid, a specific blocker for SERCA, or by high concentrations of ryanodine (50 microM). Unlike other thalamic nuclei, in the NRT the activation of high-voltage-activated Ca2+ channels failed to evoke CICR. While action potentials contributed little to the build-up of [Ca2+]i upon repetitive LTS generation, the Ca2+ released via RyR significantly reduced the number of action potentials during an LTS and reduced the neurons' low threshold activity, thus potentially reducing hypersynchronicity. This effect persisted in the presence of the SK2 channel blocker apamin. We conclude that the activation of LVACC specifically causes CICR via RyR in neurons of the NRT, thereby adding a Ca2+-dependent intracellular route to the mechanisms determining rhythmic oscillatory bursting in this nucleus.