Deep brain stimulation of the subthalamic nucleus in PD: an analysis of the exclusion causes

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Abstract

Objective: Deep Brain Stimulation (DBS) of the Subthalamic Nucleus (STN) represents a proper choice for the treatment of advanced Parkinson's disease (PD). A correct selection of the patients as candidates for the surgery is essential for a good outcome. In this study, we analyzed the exclusion causes of a series of PD patients hospitalized for the selection protocol. Methods: Ninety-eight PD patients as potential candidates for the STN DBS were studied. All patients were hospitalized and underwent a clinical evaluation of the PD stage, a levodopa challenge, a MR of the brain and a neuropsychological assessment. Results: The percentage of subjects considered not suitable for the surgery was 29.6%. A single cause of exclusion was present in 65.5% of not suitable patients, while multiple causes were present in 34.5%. The most frequent cause of exclusion was the finding of neuropsychological or psychic disorders (48.3%); in 37.9% of the patients, the motor disability was not severe enough to justify the surgery, while in 31%, we found relevant abnormalities at the brain MR. Three patients (10.3%) were poorly motivated for the surgery, while in three others (10.3%), we found a significant illness other than PD. Conclusions: The finding that about 30% of the PD patients potentially suitable for STN DBS presents some exclusion causes underlines the importance of a careful selection of the candidates for this surgery.

Introduction

The advanced phase of Parkinson's disease (PD) is mainly characterized by motor fluctuations (wearing offs, on–off phenomena) and drug-induced dyskinesias, related to the chronic dopaminergic treatment [1]. These complications often account for a significant worsening of the quality of life of PD patients [2]; for this reason, in the last years, surgical therapy was reconsidered as a good option for the treatment of advanced PD, when it is impossible to achieve a satisfactory clinical response by the pharmacological treatment [3], [4]. At present, Deep Brain Stimulation (DBS) of the Subthalamic Nucleus (STN) represents an effective therapy for PD, improving all cardinal symptoms of the disease (tremor, rigidity, akinesia) [5], [6], [7], [8] and allowing a significant reduction of the daily levodopa dose with a consequent improvement of drug-induced dyskinesias [9].

The selection of the PD patients candidates for STN DBS is a basic step to assure a satisfactory outcome of the surgical therapy; the aim of this study was to retrospectively analyze a large series of PD patients hospitalized for the protocol selection, in order to determine the percentage of subjects considered not suitable for the surgery and to identify the different exclusion motivations. All the patients hospitalized respected the following general inclusion criteria: a diagnosis of idiopathic PD, the presence of motor fluctuations and drug-induced dyskinesias, an age lower than 70 years and the absence of important medical diseases.

During the period of admission to hospital, the severity of motor fluctuations and dyskinesias was evaluated. We performed a supramaximal levodopa test, an MR of the brain and a neuropsychological assessment.

Section snippets

Methods

We examined 98 patients, 40 women and 58 men; the mean age of the patients was 61 years (S.D. 5.9); the mean duration of the disease was 14 years (S.D. 5.2) with an average duration of levodopa therapy of 12.8 years (S.D. 5.2). The duration of the period with motor fluctuations and drug-induced dyskinesias was 6.1 years (S.D. 4.4).

The patients were hospitalized to undergo the following diagnostics.

(a) Hematochemistry and serology, chest X-ray and electrocardiogram to confirm the absence of any

Results

We identified 29 subjects (29.6%) not suitable for STN DBS; 19 patients (65.5%) showed a single exclusion condition, while 10 patients (34.5%) showed multiple conditions not compatible with the surgery (Table 1).

The mean age of the patients excluded (group A) was 62 years (S.D. 5.7), while the patients included (group B) showed a mean age of 60.7 years (S.D. 6); the mean duration of PD was 12.5 years (S.D. 5.5) for the group A and 14.7 years (S.D. 5) for the group B, with a mean duration of

Discussion

We report the data relative to the exclusion conditions for the surgical procedure of bilateral STN DBS in a large pool of PD patients. This surgical treatment is only effective in patients affected by idiopathic PD and the degree of the improvement of the motor symptoms seems to be proportional to the pre-operative response to levodopa [20] or apomorphine [21].

We found a single or multiple exclusion conditions in a relatively large percentage of patients (about 30%); the most frequent cause of

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