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Michael Pourfar, Chengke Tang, Tanya Lin, Vijay Dhawan, Michael G. Kaplitt and David Eidelberg

Object

The authors investigated whether the insertion of deep brain stimulation electrodes into the subthalamic nucleus can alter regional brain metabolism in the absence of stimulation.

Methods

Six patients with Parkinson disease (PD) underwent preoperative FDG PET scanning, and again after STN electrode implantation with stimulation turned off.

Results

Compared with baseline values, glucose utilization was reduced in the postoperative off-stimulation scans in the putamen/globus pallidus and in the ventral thalamus (p < 0.01), and there was increased metabolism in the sensorimotor cortex and cerebellum (p < 0.005). The expression of a specific PD-related spatial covariance pattern measured in the FDG PET data did not change after electrode implantation (p = 0.36), nor was there a significant change in clinical motor ratings (p = 0.44). Differences in PD-related spatial covariance pattern expression among the patients after electrode implantation did, however, correlate with the number of microelectrode recording trajectories placed during surgery (r = –0.82, p < 0.05).

Conclusions

These findings suggest that electrode implantation can impart a microlesion effect on regional brain function. Nonetheless, these local changes did not cross the threshold of network modulation needed to achieve clinical benefit.

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Michael H. Pourfar, Chris C. Tang, Alon Y. Mogilner, Vijay Dhawan and David Eidelberg

The frequency with which patients with atypical parkinsonism and advanced motor symptoms undergo deep brain stimulation (DBS) procedures is unknown. However, the potential exposure of these patients to unnecessary surgical risks makes their identification critical. As many as 15% of patients enrolled in recent early Parkinson disease (PD) trials have been found to lack evidence of a dopaminergic deficit following PET or SPECT imaging. This suggests that a number of patients with parkinsonism who are referred for DBS may not have idiopathic PD. The authors report on 2 patients with probable psychogenic parkinsonism who presented for DBS surgery. They found that both patients had normal caudate and putamen [18F]-fluorodopa uptake on PET imaging, along with normal expression of specific disease-related metabolic networks for PD and multiple system atrophy, a common form of atypical neurodegenerative parkinsonism. The clinical and PET findings in these patients highlight the role of functional imaging in assisting clinical decision making when the diagnosis is uncertain.