Does early verbal fluency decline after STN implantation predict long-term cognitive outcome after STN-DBS in Parkinson's disease?

BACKGROUNDS An early and transient verbal fluency (VF) decline and impairment in frontal executive function, suggesting a cognitive microlesion effect may influence the cognitive repercussions related to subthalamic nucleus deep brain stimulation (STN-DBS). METHODS Neuropsychological tests including semantic and phonemic verbal fluency were administered both before surgery (baseline), the third day after surgery (T3), at six months (T180), and at an endpoint multiple years after surgery (Tyears). RESULTS Twenty-four patients (mean age, 63.5 ± 9.5 years; mean disease duration, 12 ± 5.8 years) were included. Both semantic and phonemic VF decreased significantly in the acute post-operative period (44.4 ± 28.2% and 34.3 ± 33.4%, respectively) and remained low at 6 months compared to pre-operative levels (decrease of 3.4 ± 47.8% and 10.8 ± 32.1%) (P < 0.05). Regression analysis showed phonemic VF to be an independent factor of decreased phonemic VF at six months. Age was the only independent predictive factor for incident Parkinson's disease dementia (PDD) (F (4,19)=3.4, P<0.03). CONCLUSION An acute post-operative decline in phonemic VF can be predictive of a long-term phonemic VF deficit. The severity of this cognitive lesion effect does not predict the development of dementia which appears to be disease-related.