Abstract
Electrode implantation into the subthalamic nucleus for deep brain stimulation in Parkinson's disease (PD) is associated with a temporary motor improvement occurring prior to neurostimulation. We studied this phenomenon by functional magnetic resonance imaging (fMRI) when considering the Unified Parkinson's Disease Rating Scale (UPDRS-III) and collateral oedema. Twelve patients with PD (age 55.9± (SD)6.8 years, PD duration 9–15 years) underwent bilateral electrode implantation into the subthalamic nucleus. The fMRI was carried out after an overnight withdrawal of levodopa (OFF condition): (i) before and (ii) within three days after surgery in absence of neurostimulation. The motor task involved visually triggered finger tapping. The OFF/UPDRS-III score dropped from 33.8±8.7 before to 23.3±4.8 after the surgery (p<0.001), correlating with the postoperative oedema score (p<0.05). During the motor task, bilateral activation of the thalamus and basal ganglia, motor cortex and insula were preoperatively higher than after surgery (p<0.001). The results became more enhanced after compensation for the oedema and UPDRS-III scores. In addition, the rigidity and axial symptoms score correlated inversely with activation of the putamen and globus pallidus (p<0.0001). One month later, the OFF/UPDRS-III score had returned to the preoperative level (35.8±7.0, p = 0.4).In conclusion, motor improvement induced by insertion of an inactive electrode into the subthalamic nucleus caused an acute microlesion which was at least partially related to the collateral oedema and associated with extensive impact on the motor network. This was postoperatively manifested as lowered movement-related activation at the cortical and subcortical levels and differed from the known effects of neurostimulation or levodopa. The motor system finally adapted to the microlesion within one month as suggested by loss of motor improvement and good efficacy of deep brain stimulation.
Highlights
Deep brain stimulation of the subthalamic nucleus (STN DBS) has become an effective treatment for Parkinson’s disease (PD) [1]
In the six patients examined one day after surgery, the OFF state UPDRS-III decreased by 24% (p,0.05) and in the other six patients examined three days after surgery decreased by 33% (p,0.01)
Microlesion is very common, and the collateral oedema appears to be co-responsible for its effect in the early postoperative phase
Summary
Deep brain stimulation of the subthalamic nucleus (STN DBS) has become an effective treatment for Parkinson’s disease (PD) [1]. Insertion of the intracerebral electrode into the brain tissue itself may contribute to clinical improvement from DBS [2,3,4]. A micro-subthalamotomy from DBS electrode implantation is manifested by smaller, though still demonstrable motor improvement in the absence of neurostimulation. It is usually already manifested during the surgery by a mild decrease of rigidity, akinesia and tremor and can remain noticeable for months after implantation in the OFF state [7]. The size of microlesion depends on the surgical techniques as the size of the microlesion grows parallel to the number of micro-electrodes passing through STN in correlation to postoperative motor improvement [10]
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