Globus Pallidus internus deep brain stimulation: An alternative treatment for Epilesia partialis continua

Resective surgery may involve an unacceptable risk of permanent neurological deficits in drug-resistant epilepsies so alternative strategies are required. In this regard, palliative neuromodulation has shown promise [[1]]. Epilepsia partialis continua (EPC) is an epileptic syndrome defined as a subclass of focal motor status epilepticus manifesting with frequent repetitive epileptic myoclonia affecting the limbs and/or face, usually arrhythmic. Even if its course and underlying aetiologies are largely heterogeneous, EPC frequently tends to become highly medically refractory [[2]]. However, due to the early involvement of the primary motor cortex, resective epilepsy surgery carries an inherent functional risk. Here we report the first clinical and neurophysiological data obtained in a patient suffering from EPC and receiving unilateral globus pallidus internus (GPi) deep brain stimulation (DBS) treatment, who was implanted with a novel sensing-enabled neurostimulator.
A 32-year-old patient with unremarkable personal and family medical history started his epilepsy in 2008 by right focal motor seizures characterized by left brachiofacial myoclonus and secondary tonic-clonic bilateralisations. Seizures were initially controlled by single antiepileptic medication (AED). MRI was normal. Extensive workup including search for an inflammatory, infectious or paraneoplastic aetiology was negative. In 2017, without any contributing factors, his epilepsy gradually worsened to chronic persistent non-progressive EPC 3a [[3]] despite adequate medication. One year of vagus nerve stimulation (VNS) was ineffective and he developed permanent left brachiofacial myoclonus with progressive hemiparesis. EEG showed continuous spike-and-wave pseudo-periodic activity concomitant with myoclonic activity (see supplemental data). Due to the high functional risk carried by primary motor cortectomy, a unilateral right quadripolar Percept PC DBS electrode (Medtronic 3389) was implanted in the sensorimotor part of the GPi without per- or postsurgical complications. Therapy was provided as a humanitarian device. DBS electrode localisation was confirmed using the advanced processing pipeline in Lead-DBS (see supplemental Data for coordinates) [[4]]. AED and VNS were not discontinued.
The patient was monitored three times a week during the month following implantation by three independent neurologists expert in epilepsy and DBS programming (DG/JA/EC). DBS efficacy was evaluated using both visual analogic scale (VAS) and actigraphy recordings (MotionWatch8, Cambridge Neurotechnology, UK, Fig. 1a). Effectiveness was assessed with different monopolar stimulation settings: best stimulation results were obtained with contacts 0 and 1, pulse-width 60μs, frequency 130 Hz, amplitude 3mA. The electrode was connected to a sensing-enabled Percept PC neurostimulator allowing regular local field potential (LFP) recordings with or without stimulation, at rest with eyes closed (bipolar montage between two adjacent contacts, sampling frequency of 250Hz, low pass filter at 100Hz and high pass filter at 1Hz). Systematic bipolar recordings performed off stimulation revealed LFP oscillations in the low beta band (14Hz; between each pair of adjacent contacts). This target frequency was selected for chronic recordings when stimulation was switched on (recordings between contacts 0 and 2, stimulation through contact 1). Post-hoc time-frequency (TF) and power spectrum density (PSD) analyses were performed at day 5 (beginning of daily follow-up) and day 28 (end of daily follow-up) after implantation.