GPi-Targeted DBS Placement using Optic Tract Stimulated VEP and Corticospinal Tract Stimulation in a Case of Severe Primary Dystonia

Keywords

visual evoked potentials - dystonia - GPi

Introduction: Optical tract stimulated visual evoked potential (VEP) is useful during deep brain stimulation (DBS) in the globus pallidus internum (Gpi) for the treatment of primary dystonia. Recordings of cortical VEPs obtained after stimulation of the optic tract may be a potential option to microelectrode recordings (MERs), since optic tract lies just beneath the best target for Gpi DBS.

Methodology/Description: A 25-year-old patient with severely symptomatic dystonia on multiple drugs was posted for DBS placement into GPi. Awake DBS placement was ruled out (severe symptoms with opisthotonus paroxysms every 15 to 20 minutes and noncooperative). The patient received all drugs for dystonia on the day of surgery. Once shifted into OT, baseline VEPs were recorded with LED goggles. Then general anesthesia was induced with fentanyl, propofol, and atracurium and changes in VEP were noted. Steady-state anesthesia with entropy-guided TIVA with propofol and dexmedetomidine was achieved where recordings of the VEP (P100) were sufficiently good. Bilateral scalp block and pin site infiltration were given to decrease the requirement of anesthetics. Computed tomography (CT) scan was done with the same infusions and atracurium boluses. On returning to the OT, the patient was repositioned and entropy reattached. Goggles and O1, O2, Oz, FZ were attached. Corticospinal tract monitoring with needle electrodes in mentalis, deltoid, adductor pollicis, and tibialis anterior was planned. Anesthesia was maintained with entropy-guided dexmedetomidine and propofol infusions and hourly fentanyl boluses targeting <60 without muscle relaxants. DBS placement was done with neuronavigation + CARM and mainly optic tract stimulation and recording N40-P70. DBS electrodes were placed at 1mm away from the distance where optic tract) VEP amplitudes were maximum and no positive corticospinal stimulation even with 5 mA current. DBS electrode placement was confirmed with intraoperative MRI after sanitization and removal of all metallic electrodes, entropy sensors, etc. Later the battery was placed and the patient was extubated.

Conclusion: Challenges faced in such GPi targeted DBS placements are enormous and careful planning and teamwork are utmost important in such cases

 

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• References

• 1 Landi A, Pirillo D, Cilia R, Antonini A, Sganzerla EP. Cortical visual evoked potentials recorded after optic tract near field stimulation during GPi-DBS in non-cooperative patients.. Clin Neurol Neurosurg 2011; 113 (02) 119-122