Deep brain stimulation of the subthalamic nucleus in Parkinson's disease: comparison of pre- and postoperative neuropsychological evaluation

https://doi.org/10.1016/S0022-510X(01)00575-5Get rights and content

Abstract

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for the motor symptoms of advanced Parkinson's disease (PD). The aim of this study was to assess the effect of the bilateral surgical procedure and STN DBS on the neuropsychological functions. Twenty Parkinson's disease patients underwent a neuropsychological assessment before and 6 months after surgery in four different conditions: medication on (with levodopa) and medication off (without levodopa) during the preoperative period, medication on/stimulation on (levodopa plus stimulators switched on) and medication off/stimulation on (stimulators switched on without levodopa) during the postoperative period. We did not find any significant difference in the four conditions for all the neuropsychological tests, confirming the lack of an overall cognitive decline after surgery. From a neuropsychological point of view, these results seem to indicate that bilateral STN DBS is a safe treatment for advanced PD.

Introduction

Recently, it has been shown that deep brain stimulation (DBS) of the subthalamic nucleus (STN) [1], [2], [3], [4] and of the internal globus pallidus (GPi) [5], [6], [7], [8] is an effective therapy for advanced Parkinson's Disease (PD). The main clinical features of the advanced phase of the disease are represented by motor fluctuations (wearing offs, on–off phenomena) and levodopa-induced involuntary movements, with a difficult to achieve satisfactory quality of life through dopaminergic therapies [9], [10]. Bilateral STN DBS seems to be more effective with respect to bilateral GPi DBS and it allows a significant reduction of the amount of dopaminergic drugs with a consequent improvement of dyskinesias [4], [6], [11]. Moreover, the effects of STN DBS seem to persist in the long-term follow-up [12].

The principal advantages of the DBS procedures are the reversibility, the possibility to modify the stimulator parameters according to patients needs and the minor incidence of side effects [13]. The last one is relevant with respect to the lesioning procedures; in fact, it has been reported that unilateral pallidotomy can be responsible for cognitive impairment of patients, and a bilateral lesioning procedure of GPi greatly increases this risk [14]. However, the effects of DBS on cognitive functions are still little known; in particular, it is relevant to investigate whether the surgical procedure can negatively interfere with the cognitive performances or, on the contrary, whether the functional inhibition of a hyperactive target in PD can modify the non-motor basal ganglia-thalamo-cortical circuits with an effect on the cognitive processing.

A recent study [15] analysed a large series of PD patients who underwent bilateral implantation of stimulating electrodes in STN or GPi; a high percentage of patients were examined before and after surgery without levodopa, and all patients were assessed in the stimulation on condition after surgery. The main result was the lack of any significant cognitive side effects for both surgical procedures; the neuropsychological profile of the patients was unchanged after 3–6 months of STN or GPi DBS, except for a decrease in verbal fluency and an improvement in the Trail Making B test observed only in the patients implanted in the STN. In a successive study, an improvement in psychomotor speed (reaction times tasks, Trail Making, Stroop test) and in working memory was reported in STN-implanted patients evaluated in the stimulation on/medication on condition, while a mild category fluency deficit was observed in the stimulation on/medication off condition [16].

Others authors [14] suggested the presence of a cognitive decline of PD patients after bilateral STN DBS; in this case, the assessed pattern of neuropsychological modifications was similar to that observed in patients affected by progressive supranuclear palsy (PSP), and it was observed only in patients older than 69.

We studied 20 consecutive PD patients to verify whether bilateral STN DBS could be responsible for neuropsychological alterations.

Section snippets

Subjects

We studied 20 right-handed PD patients (12 men and 8 women) bilaterally implanted for STN DBS. The mean age of the patients at the time of the surgery was 61.6 years (6 SD); the mean duration of the illness was 15.4 years (4.9 SD), with a mean duration of the levodopa treatment of 14.3 years (5.2 SD). The mean Hoehn and Yahr [17] stage was 2.5 (0.3 SD) in the on phase and 4 (0.4 SD) in the off phase. The principal inclusion criteria for the surgical therapy were: (a) the presence of severe

Results

The STN DBS led to a significant improvement of the PD symptoms in all the patients. In Table 1, we reported the data relative to the UPDRS sub-scores in the four different conditions, the preoperative med on and med off, and the postoperative stim on/med off and stim on/med on.

Table 2(a) shows the findings relative to the memory analysis. All the tests (Rivermead, Spatial Learning, Paired Associate Learning, Corsi's Block Tapping and Bi-sillabic Words Repetition) showed no significant

Discussion

The effect of STN DBS on cognitive functions in PD patients is a relevant issue for the confirmation of the safety of this surgical treatment.

The most relevant finding of our study concerns the absence of an overall cognitive decline after the surgical procedure. The comparison between the med off, the med on, the stim on/med off and the stim on/med on conditions didn't show any significant difference for all the neuropsychological functions examined; the conditions of levodopa alone, surgical

References (35)

  • P. Krack et al.

    Subthalamic nucleus or internal pallidal stimulation in young onset Parkinson's disease

    Brain

    (1998)
  • R.P. Iacono et al.

    Chronic anterior pallidal stimulation for Parkinson's disease

    Acta Neurochir. Wien

    (1995)
  • P. Krack et al.

    Opposite motor effects of pallidal stimulation in Parkinson's disease

    Ann. Neurol.

    (1998)
  • R. Pahwa et al.

    High-frequency stimulation of the globus pallidus for the treatment of Parkinson's disease

    Neurology

    (1997)
  • D.E. Riley et al.

    The spectrum of levodopa-related fluctuations in Parkinson's disease

    Neurology

    (1993)
  • W.C. Olanow et al.

    The role of deep brain stimulation as a surgical treatment for Parkinson's disease

    Neurology

    (2000)
  • M.C. Rodriguez-Oroz et al.

    Bilateral deep brain stimulation of the subthalamic nucleus in Parkinson's disease

    Neurology

    (2000)
  • Cited by (0)

    View full text