Impact of intraoperative physiologic target localisation on outcome following subthalamic deep brain stimulation

Objective: To compare the outcome in two series of patients with Parkinson's disease (PD) treated by subthalamic deep brain stimulation (STN-DBS) either using intraoperative macrostimulation alone or multitrajectory microelectrode mapping (MMM).

Background: The implantation of electrodes for STN-DBS requires intraoperative neurophysiological verification. This may be achieved by macrostimulation alone or by combined microrecording and -stimulation. There is a debate on the possible benefits and risks of MMM, but few available data.

Methods: We retrospectively analysed 39 PD patients who received STN-DBS between 1998 and 2002 in centre 1 (Dept. of Stereotactic and Functional Neurosurgery, Cologne) and 50 PD patients operated between 1999 and 2003 in centre 2 (Dept. of Neurosurgery, Kiel). Patients were followed for at least 3 years at the Depts. of Neurology in Düsseldorf and Kiel. Within the study period centre 1 used CT- and MRI-guided stereotactic target planning and intraoperative macrostimulation. Subsequent trajectories were only explored if stimulation did not result in favourable symptom reduction. Centre 2 used MRI-based target planning and MMM by 5 test electrodes. Motor outcome was assessed by the motor part of the UPDRS. Because STN-DBS should ideally mimic the preoperative response to l-dopa, we used the ratio R between the motor score on-medication before surgery and on-stimulation/off-medication after surgery to evaluate surgical success. A ratio<1 indicates less and >1 better effect of DBS compared to l-dopa.

Results: In both groups, age at operation (61.1±5.4 vs. 58.8±10.5), disease duration (16.1±6.9 vs. 16.6±6.1) and preoperative levodopa equivalent dosage (LEDD) (948±388 vs. 993±405mg) were comparable (P>0.05). At 6 months follow-up, there was no difference in efficacy of STN-DBS (R 0.91±0.28 vs. 1.02±0.81, P>0.05) at both centres. At long-term follow-up (49.3 vs. 46.6 months), however, group 1 showed significantly reduced stimulation efficacy (R 0.40±0.56) compared to group 2 (R 0.95±0.59). Stimulation parameters and LEDD reduction were identical. There was no intracerebral hemorrhage in either group.

Conclusions: Intraoperative physiological target localisation by either intraoperative MMM or macrostimulation results in comparable short-term motor outcome. MMM did not cause higher perioperative morbidity. The better long-term efficacy in group 2 could indicate an advantage of MMM in defining the optimal physiological target for STN-DBS.