Publicado em: 20/07/2010
A Randomized Trial of Deep-Brain Stimulation for Parkinson's Disease
Background Neurostimulation of the subthalamic nucleus reduces levodopa-related motor complications in advanced Parkinson's disease. We compared this treatment plus medication with medical management.
Methods In this randomized-pairs trial, we enrolled 156 patients with advanced Parkinson's disease and severe motor symptoms. The primary end points were the changes from baseline to six months in the quality of life, as assessed by the Parkinson's Disease Questionnaire (PDQ-39), and the severity of symptoms without medication, according to the Unified Parkinson's Disease Rating Scale, part III (UPDRS-III).
Results Pairwise comparisons showed that neurostimulation, as compared with medication alone, caused greater improvements from baseline to six months in the PDQ-39 (50 of 78 pairs, P=0.02) and the UPDRS-III (55 of 78, P<0.001), with mean improvements of 9.5 and 19.6 points, respectively. Neurostimulation resulted in improvements of 24 to 38 percent in the PDQ-39 subscales for mobility, activities of daily living, emotional well-being, stigma, and bodily discomfort. Serious adverse events were more common with neurostimulation than with medication alone (13 percent vs. 4 percent, P<0.04) and included a fatal intracerebral hemorrhage. The overall frequency of adverse events was higher in the medication group (64 percent vs. 50 percent, P=0.08).
Conclusions In this six-month study of patients under 75 years of age with severe motor complications of Parkinson's disease, neurostimulation of the subthalamic nucleus was more effective than medical management alone. (ClinicalTrials.gov number, NCT00196911 [ClinicalTrials.gov] .)
Parkinson's disease is one of the most disabling chronic neurologic diseases and leads to a significant loss of quality of life.1,2 Several drugs are available that can effectively treat the symptoms of the disease, but long-term medical management is often complicated by the appearance of levodopa-induced motor complications, leading to rapid changes between periods of severe akinesia and periods of mobility that may be accompanied by troublesome hyperkinesias.3 Dopamine agonists, amantadine, catechol O-methyltransferase (COMT) inhibitors,3 and other drugs can effectively improve mobility and reduce dyskinesias initially but typically fail after several years.4
The administration of high-frequency continuous electrical stimulation to the subthalamic nucleus through a surgically implanted device has been shown to improve motor symptoms in patients with advanced stages of Parkinson's disease.5,6 In open follow-up studies, mobility was significantly improved, and dyskinesias were dramatically reduced for up to five years.7 However, this therapy will be acceptable to patients only if the symptomatic benefits are greater than the inherent surgical risks and reduce the burden of disease more effectively than optimal drug therapy. Parkinson's disease interferes with various aspects of the quality of life, particularly those related to physical and social functioning.1,2 We performed a randomized, controlled trial comparing neurostimulation with the best medical management over a six-month period. Changes in the quality of life and motor function, the latter assessed while the patient was not receiving medication, were the primary outcome measures.
Patients were eligible for enrollment if they had received a clinical diagnosis of idiopathic Parkinson's disease according to the British Parkinson's Disease Society Brain Bank criteria8 at least five years previously; were under 75 years of age; had parkinsonian motor symptoms or dyskinesias that limited their ability to perform the activities of daily living, despite receipt of optimal medical therapy; had no dementia or major psychiatric illness; and had no contraindications to surgery. Neurologists specializing in movement disorders at the participating centers gave their assurance that each patient had received state-of-the-art antiparkinsonian medication.9
Study Design and Outcomes
This study was an unblinded trial with a randomized-pairs design comparing deep-brain stimulation of the subthalamic nucleus with best medical management. The trial was conducted at 10 academic centers in Germany and Austria. The protocol was approved by the ethics committee at each participating center. All patients provided written informed consent.
The centers enrolled patients in pairs, with one patient randomly assigned to neurostimulation within six weeks after enrollment and the other to best medical treatment. Randomization, monitoring, and data management were performed by the Coordinating Center for Clinical Trials at Philipps University, Marburg, Germany. The primary end points were the changes from baseline to six months in the quality of life, as assessed by the Parkinson's Disease Questionnaire (PDQ-39) summary index,10,11 and in the severity of motor symptoms while the patient was not taking medication, as assessed by the Unified Parkinson's Disease Rating Scale, part III (UPDRS-III).12 Scores for the PDQ-39 can range from 0 to 100, with higher scores indicating worse function. Scores for the UPDRS-III can range from 0 to 108, with higher scores indicating poorer condition. Patients were assessed after a 12-hour overnight withdrawal of antiparkinsonian medication and while they were taking medication, after the administration of a dose of liquid levodopa that was 50 percent higher than the usual morning dose of dopaminergic medication. When they are not taking medication, patients whose disease is severe enough to meet the criteria for inclusion in this trial are typically immobile, requiring help with the activities of daily living or being confined to bed or a wheelchair; however, the use of medication may not enable them to become completely mobile.
The secondary outcome measures included changes in a dyskinesia scale13 and in the activities of daily living as assessed by the Unified Parkinson's Disease Rating Scale, part II (UPDRS-II), and the Schwab and England Scale,12 with and without medication. Scores for the dyskinesia scale can range from 0 to 28, with higher scores indicating more severe dyskinesia. Scores for the UPDRS-II can range from 0 to 52, with higher scores indicating poorer function. Scores for the Schwab and England Scale can range from 0 to 100, with higher scores indicating better function. Motor symptoms (according to the UPDRS-III12) were also assessed while the patient was taking medication, as were cognitive function (according to the Mattis Dementia Rating Scale, for which scores can range from 0 to 144, with lower scores indicating more severe dementia14), neuropsychiatric function (according to the Montgomery and Asberg Depression Rating Scale15 and the Brief Psychiatric Rating Scale,16for which scores can range from 0 to 60 and 18 to 126, respectively, and higher scores indicate more severe depression and poorer mental health, respectively), and the health-related quality of life (according to the Medical Outcomes Study 36-item Short-Form General Health Survey [SF-36] physical and mental summary scores, which are obtained by norm-based scoring, with higher scores indicating a better quality of life17).
Using diaries that separated the day into half-hour segments, the patients recorded their mobility during the three days before admission and for another three days six months after admission. They were trained to rate their condition as sleeping, immobile, neither fully mobile nor fully immobile, mobile without troublesome dyskinesias, or mobile with troublesome dyskinesias. The total number of hours spent in each of these categories was calculated, and the differences between the baseline and the six-month scores were compared between the groups. To compare the effects of changes in antiparkinsonian medications, we calculated that a 100-mg daily dose of standard levodopa was equivalent to the following doses of other medications: 133 mg of controlled-release levodopa; 75 mg of levodopa plus entacapone; 1 mg of pergolide, pramipexole, lisuride, or cabergoline; 5 mg of ropinirole; 10 mg of bromocriptine or apomorphine; and 20 mg of dihydroergocriptine.
Safety was assessed by recording the frequency and severity of reported adverse events. Any new symptom or worsening of a preexisting symptom was classified as an adverse event.
Patients assigned to neurostimulation underwent bilateral stereotactic surgery under local anesthesia. The subthalamic nucleus was targeted by means of stereotactic magnetic resonance imaging, ventriculography, microelectrode recording, or a combination of these techniques; the techniques used varied among the centers according to the institutional surgical protocols. The anatomical target coordinates were confirmed to be 0 to 3 mm behind the midcommisural point, 4 to 6 mm below the intercommisural line, and 11 to 13 mm lateral to the midplane of the third ventricle. The final implantation point was the position at which the most pronounced effect on rigidity and other symptoms of Parkinson's disease was obtained at the lowest stimulation intensity and with the largest safety margin (as determined by the difference in the intensity of stimulation between the clinical effect and the occurrence of unwanted effects) during intraoperative testing. The permanent electrode (model 3389 DBS, Medtronic) and the pulse generator (Kinetra, Medtronic) were implanted, and the final position of the electrode was confirmed by neuroimaging. Postoperatively, the optimal stimulation settings and antiparkinsonian medication were progressively adjusted according to the patient's response. The standard pulse setting was 60 µsec in duration at 130 Hz, with voltage adjusted to the individual patient.
Patients assigned to medical treatment received individualized optimal drug therapy according to the guidelines of the German Society of Neurology.9 The drugs were adjusted according to the patient's needs throughout the study.
On the basis of earlier treatment results,18 we determined that 77 patients would need to be enrolled in each treatment group to detect a mean difference of 0.5 SD (using a two-sided test with an value of 0.05 and a value of 0.2, and assuming a dropout rate of 20 percent) between the groups. Primary outcome analysis was conducted according to the intention-to-treat principle. The primary outcome variables were the changes in a patient's scores from baseline to six months. For each primary end point, we subtracted the change in scores for the partner treated with medication from the change in scores for the partner treated with neurostimulation and tested the significance of the pairwise differences using the sign test. The nominal significance level for the final analysis was set to 0.04806 (two-sided), with adjustment for a planned interim analysis after follow-up of the first 38 pairs at a nominal level of 0.005.19 In the confirmatory analysis, missing follow-up values for the PDQ-39 summary index and the UPDRS-III scores while the patient was not taking medication were imputed to be the highest (worst) score for the neurostimulation group and the lowest (best) score for the medication group. This is a strictly conservative analytic strategy. The study outcome was considered to be positive only if the neurostimulation group had significantly better results for both primary end points than the medication group.
The secondary outcome values were the changes from baseline to six months in scales that measured the severity of the disease. All analyses of the secondary outcomes were descriptive. To address problems arising from missing values, the Wilcoxon–Mann–Whitney test for independent samples was applied, despite the pairwise data structure. The chi-square test was used for categorical data. Statistical analyses were performed with the SAS statistical package, version 8.02.
Of 196 patients who were screened between 2001 and 2004, 178 were randomly assigned to neurostimulation or best medical treatment (Figure 1). Twenty-two patients at one center were excluded from the analysis because the patients assigned to medical treatment were advised to return for immediate surgery in case of insufficient improvement. The center was closed after consultation with the monitoring committee. The treatment results among these excluded patients did not differ significantly from those in the intention-to-treat population; the excluded patients were not included in the analysis of adverse events. The intention-to-treat population thus consisted of 78 pairs of patients (156 patients) who were successfully randomly assigned to treatment. There were no significant differences in important baseline characteristics between the two treatment groups (Table 1).
According to the intention-to-treat analysis of the 78 pairs of patients, in 50 pairs, the patient treated with neurostimulation had greater improvement in the score on the PDQ-39 summary index than did the patient assigned to medical treatment (P=0.02), and in 55 pairs, the patient treated with neurostimulation had greater improvement in the score on the UPDRS-III administered when the patients were not taking medication (P<0.001) (Table 2). This favorable result was obtained despite rigid criteria for the replacement of missing data that gave an advantage to medical treatment in the results. Therefore, neurostimulation was considered superior to medical treatment.
The mean PDQ-39 summary index score was 41.8±13.9 at baseline and 31.8±16.3 at six months in the neurostimulation group, as compared with 39.6±16.0 and 40.2±14.4, respectively, in the medication group (Table 3). This result corresponds to an improvement of about 25 percent in the neurostimulation group as compared with practically no change in the medication group. Treatment with neurostimulation resulted in a 22 percent improvement in the physical summary score of the SF-36, a generic quality-of-life scale (Table 3). We performed a secondary sensitivity analysis of the findings for the primary outcome criteria on a per-protocol basis; this analysis also showed that the outcome was better among patients treated with neurostimulation than among those who received medical treatment: in 45 of 60 pairs, the patient treated with neurostimulation had greater improvement in the score on the PDQ-39 summary index than the patient who received medical treatment (P<0.001) and in 51 of 60 pairs, the patient treated with neurostimulation had greater improvement in the UPDRS-III score (P<0.001).
Individual domains of the PDQ-39 were affected differently by treatment (Figure 2A). Improvements of 24 to 38 percent were obtained for mobility, activities of daily living, emotional well-being, stigma, and bodily discomfort. In contrast, there was no improvement in social support, cognition, or communication. The greatest improvement occurred in activities of daily living, a result consistent with the significant improvement in other secondary outcome values that measure the extent of impairment in daily life (the UPDRS-II and the Schwab and England Scale).
The effect of neurostimulation on motor symptoms was assessed with the use of the UPDRS-III while the patient was not taking medication. The mean score improved from 48.0±12.3 at baseline to 28.3±14.7 at six months in the neurostimulation group, an improvement of 41 percent, but remained unchanged in the medication group (46.8±12.1 at baseline and 46.0±12.6 at six months). The UPDRS-III score obtained while the patient was taking medication improved in the neurostimulation group from 18.9±9.3 at baseline to 14.6±8.5 at six months but remained unchanged in the medication group (17.3±9.6 at baseline and 17.5±10.6 at six months).
The secondary outcome measures were selected to identify additional disease dimensions that are improved with treatment. Activities of daily living while the patient was not taking medication, as assessed by the UPDRS-II, markedly improved (by 39 percent) in the neurostimulation group and slightly worsened (by 5 percent) in the medication group. A small difference in favor of neurostimulation was also observed in this scale when the patients were taking medication. Impairment, as measured by the Schwab and England Scale with and without medication, improved in the neurostimulation group and worsened in the medication group. Emotional and cognitive measures did not differ significantly between the neurostimulation and the medication groups, but the mental summary score of the SF-36 showed a small but significant improvement of 7 percent in the neurostimulation group (Table 3).
Scores on the dyskinesia scale obtained while the patient was not taking medication improved from 6.7±5.3 to 3.1±3.5 (54 percent) in the neurostimulation group but remained unchanged in the medication group. The patients' diaries showed profound and significant changes from baseline to six months in the neurostimulation group alone (Figure 2B). The period of immobility was reduced by 4.2 hours and the period of mobility without dyskinesias was increased by 4.4 hours. The time spent sleeping was increased by 0.7 hour. The period of mobility with troublesome dyskinesias was also significantly reduced.
The mean values for the stimulation settings were as follows: amplitude, 2.9±0.6 V; frequency, 139±18 Hz; and pulse duration, 63±7.7 µsec. The dopaminergic equivalents were reduced by 50 percent for the neurostimulation group and by 8 percent for the medication group (Table 3).
Thirteen severe adverse events were reported in 13 patients: 10 in the neurostimulation group and 3 in the medication group (12.8 percent and 3.8 percent, respectively; P=0.04) (Table 4). Three patients died in the neurostimulation group: one died as a result of intracerebral hematoma incurred during surgery, one died from pneumonia that developed six weeks after randomization, and one committed suicide five months after randomization. One patient in the medication group died in a motor vehicle accident, caused because he was driving during a psychotic episode. All other severe adverse events resolved without permanent complications (Table 4). A total of 173 adverse events were reported in 89 patients: 39 (50.0 percent) in the neurostimulation group and 50 (64.1 percent) in the medication group (P=0.08). Most adverse events were well-known medical problems associated with advanced Parkinson's disease.
This trial demonstrated the superior efficacy of neurostimulation over best medical management in patients with advanced Parkinson's disease and levodopa-related motor complications. Previous "proof-of-principle" studies,5,6 which did not include prospective control groups, showed that subthalamic neurostimulation improved fluctuating mobility and dyskinesias for up to five years.7 In our study, neurostimulation was associated with a 25 percent improvement in the PDQ-39 summary index, which is within the range of the improvements described in uncontrolled case series21,22 and is consistent with the 22 percent improvement in the SF-36, a generic quality-of-life scale.
In contrast to many previous studies of Parkinson's disease, which focused on motor scales, we used quality-of-life measures as the primary outcome criteria.5,7,23,24,25 Factors in addition to motor function contribute to such a complex variable as the quality of life. First, complications of surgery or medication are frequent and may decrease the quality of life, despite improvement in motor signs. Second, there is an ongoing discussion about whether the detrimental effects on cognition,26,27 mood,28 and behavior29 that have been observed in prior studies of neurostimulation were related to surgery, to stimulation itself, or to disease, medication, or a potential selection bias. Finally, depression has a greater effect than motor symptoms on the quality of life,30 so that neuropsychiatric adverse effects could cancel out motor benefits. Therefore, a controlled clinical trial measuring the quality of life was necessary. Our findings suggest that despite all these possible confounders, neurostimulation is superior to medical treatment alone for patients similar to those in our study.
How strong are the clinical effects of neurostimulation? Before surgery, the PDQ-39 summary index scores of the patients in the study were similar to those of a group of patients who needed help in everyday situations,31 and after surgery, their scores were similar to those of a mobile cohort without balance problems.31 The effects of neurostimulation can also be compared with the effects of drugs, which are usually smaller. For example, a placebo-controlled trial of rasagiline showed a significant improvement of 2.9 points32 in the PDQ-39 summary index, and a trial of entacapone, a drug with a well-documented effect on the motor score,33 showed no improvement in the quality of life.34 Finally, the minimum clinically relevant difference (i.e., the difference that a patient would consider to be an improvement) in the score for the PDQ-39 summary index can be used as an estimate of the strength of treatment effects.35 In one study, this difference was found to be 0.6 point.35 Thus, the improvement of about 10 points observed in our study would be considered to represent a strong effect.
What accounts for this strong improvement? Improvements in the scores on the PDQ-39 subscales for mobility and activities of daily living reflect changes in motor aspects of the disease. Indeed, evaluation of motor performance by means of the UPDRS-III, the dyskinesia scale, and patients' diaries mainly documented a decrease in the severity and duration of periods of immobility and a decrease in the duration and severity of periods of dyskinesias among patients who received neurostimulation. Scores for emotional well-being, stigma, and bodily discomfort also improved, resulting in an improvement in the overall quality of life in the neurostimulation group. We did not find significant changes in the neuropsychologic and psychiatric evaluations. Changes in cognition or mood that may occur in individual patients as side effects of surgery or stimulation26,27,28 therefore did not seem to decrease the quality of life in the neurostimulation group as a whole.
Neurostimulation resulted in major benefits in our study, but some limitations of the study design need to be critically addressed. There was no sham-surgery group or placebo control. The use of sham surgery as a control remains controversial because of the potential side effects.36 A feasible option would be to administer placebo stimulation for a short period in a patient who is not taking medication in order to compare motor signs in the stimulated and the nonstimulated condition.5 Stimulation of the subthalamic nucleus interferes with antiparkinsonian medication, and a large decrease in the dose of such medications is mandatory to prevent motor and behavioral side effects. Therefore, a blinded comparison of neurostimulation with best medical treatment was not feasible. The control group was treated by experts in movement disorders in compliance with national guidelines for the treatment of advanced Parkinson's disease,9 but further standardization of the best medical treatment was not performed.
In conclusion, this six-month study demonstrated that subthalamic neurostimulation resulted in a significant and clinically meaningful improvement in the quality of life of patients under 75 years of age who had advanced Parkinson's disease with severe fluctuations in mobility and dyskinesia. The patients who received neurostimulation had longer periods and better quality of mobility with less dyskinesia. These changes in motor functioning led to improvement in measurements of activities of daily living, emotional well-being, stigma, and bodily discomfort. Cognition, mood, and overall psychiatric functioning were unchanged. In carefully selected patients, neurostimulation of the subthalamic nucleus is a powerful treatment that alleviates the burden of advanced Parkinson's disease. The prospect of an improved quality of life in patients treated with neurostimulation has to be weighed against the risk of complications related to surgery.
Supported by a grant (01GI0201) from the German Federal Ministry of Education and Research.
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