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Long term effects of bilateral subthalamic nucleus stimulation on cognitive 
function, mood, and behaviour in Parkinson’s disease
A Funkiewiez1, C Ardouin1, E Caputo2, P Krack1, V Fraix1, H Klinger1, S 
Chabardes1, K Foote1, A-L Benabid1 and P Pollak1

1 Department of Clinical and Biological Neurosciences, Joseph Fourier 
University, Grenoble, France
2 Department of Neurology, Ospedale San Paolo, Milan, Italy

Correspondence to:
Dr P Krack
Department of Clinical and Biological Neurosciences, Service de Neurologie, 
Centre Hospitalier Universitaire de Grenoble, BP 217, 38043 Grenoble Cedex 9, 
France; [log in to unmask]

Background: Long term effects of subthalamic nucleus (STN) stimulation on 
cognition, mood, and behaviour are unknown.

Objective: This study evaluated the cognitive, mood, and behavioural effects 
of bilateral subthalamic nucleus deep brain stimulation (STN DBS) in patients 
with Parkinson’s disease (PD) followed up for three years.

Methods: A consecutive series of 77 PD patients was assessed before, one, and 
three years after surgery. Mean (SD) age at surgery was 55 (8). Seven 
patients died or were lost for follow up. Neuropsychological assessment 
included a global cognitive scale, memory, and frontal tests. Depression was 
evaluated using the Beck depression inventory. Assessment of thought 
disorders and apathy was based on the unified Parkinson’s disease rating 
scale. Reports of the behavioural changes are mainly based on interviews done 
by the same neuropsychologist at each follow up.

Results: Only two cognitive variables worsened (category fluency, total score 
of fluency). Age was a predictor of decline in executive functions. 
Depression improved whereas apathy and thought disorders worsened. Major 
behavioural changes were two transient aggressive impulsive episodes, one 
suicide, four suicide attempts, one permanent apathy, one transient severe 
depression, four psychoses (one permanent), and five hypomania (one 
permanent).

Conclusions: Comparing baseline, one year, and three year postoperative 
assessments, STN stimulation did not lead to global cognitive deterioration. 
Apathy scores mildly increased. Depression scores mildly improved. 
Behavioural changes were comparatively rare and mostly transient. Single case 
reports show the major synergistic effects of both medication and stimulation 
on mood and behaviour, illustrating the importance of a correct postoperative 
management.

http://jnnp.bmjjournals.com/cgi/content/abstract/75/6/834

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