Phonemic verbal fluency decline after subthalamic nucleus deep brain stimulation does not depend on number of microelectrode recordings or lead tip placement

Abstract Background Evidence suggests that both motor improvement and decline in verbal fluency in Parkinson's disease (PD) patients undergoing deep brain stimulation (DBS) may be attributed to a lead implantation effect. Objective We investigated whether the number of microelectrode recording (MER) passes influenced either motor UPDRS scores just prior to stimulation initiation at 4 weeks or decline in verbal fluency 6–24 months after surgery. Methods We retrospectively analyzed 50 PD patients who underwent bilateral STN DBS. Off medication UPDRS III motor scores were obtained before surgery and before stimulation was initiated. Neuropsychological testing was completed pre- and post-operatively in 28 patients at a mean of 377 days. Coordinates of lead tip and active stimulation site were calculated. Results There was no improvement in off-medication UPDRS III motor scores at a mean 33.9 days following surgery, with mean change of 0.04 ± 10.48 ( p  = 0.98). There was no correlation between the number of MER passes and change in individual UPDRS motor score ( r  = −0.0001, p  = 1.0). We observed significant decline in phonemic verbal fluency by 16% ( p  = 0.003) but it was not correlated with number of left hemisphere ( r  = −0.15, p  = 0.46), or total number of passes ( r  = −0.02, p  = 0.94) or coordinates of the lead tip or active stimulation site. There was a trend toward correlation with age ( r  = 0.38, p  = 0.07). Conclusions Significant decline in phonemic verbal fluency did not correlate with surgical passes nor with location of the lead tip or active stimulation site. These data suggest that age may influence verbal fluency decline more than surgical technique.