Extradural cortical stimulation for movement disorders

Extradural cortical stimulation is a recent addition to the armamentarium of operative neuromodulation. Motor cortex stimulation (MCS) is offered by positioning a stimulating plate extradurally on the primary motor cortex. It is a minimally invasive technique that was originally proposed for the control of central neuropathic pain. Currently, its use has been extended to patients with movement disorders. The need for minimally invasive therapies, with low morbidity-mortality which can be applied to patients who are excluded from deep brain stimulation (DBS), led to the first attempt of MCS in Parkinson's disease (PD). Following the demonstration that transcranial magnetic stimulation (TMS) is beneficial in PD, we attempted direct extradural MCS on patients with advanced PD not meeting the criteria for DBS. The mechanisms of action may include "hyperdirect" motor cortex-subthalamic nucleus (MI-STN) input, inhibition, resynchronisation, plasticity changes, interhemispheric transfer of inhibition/excitation and modulation of other cortical areas. In this article, we review the mechanism of action of MCS in movement disorders, the predictive factors of MCS efficacy in PD, the indications, particularly in the elderly who are not suitable for DBS, the adverse effects, and the technique for localization of the central sulcus and for performing the procedure. The future prospects and developments are also discussed.