Supplementary motor area – clinical semiology and results of direct electrical stimulation during intracranial electrodes exploration

Abstract

Objectives. We aimed to study the supplementary motor area (SMA) by observing the clinical semiology of the seizures generated by an epileptogenic zone containing the SMA and by performing direct electrical stimulation (DES) of the SMA explored by means of intracranial depth electrodes using various stimulation protocols. Material and method. We invasively explored with intracerebral depth electrodes 65 patients with focal drug resistant epilepsy as presurgical evaluation. Only 5 had the SMA included in the epileptogenic zone (EZ). We recorded multiple spontaneous and provoked seizures. We applied specific DES (single pulse electrical stimulation – SPES and 50 Hz protocols) to the SMA and adjacent cerebral structures. All patients were operated on and had the EZ removed, have currently good outcomes (Engel I and II) at more than 1-year post surgery and have no neurological deficits. Results. All stereo electroencephalographic (SEEG) recorded seizures indicated the SMA as part of the EZ. Common manifestations were grimacing, version of the head to one side, tonic asymmetric posturing of the upper limbs and secondary generalization. The DES of the SMA induced forced adduction of the contralateral upper limb, flexion of the trunk to the contralateral side, clonia of the contralateral lower limbs. SPES stimulation revealed SMA connectivity with various frontal and parietal structures, as well as the influence of sleep on these connections. Discussion. SMA as part of the EZ elicited seizures with varying and complex clinical features, with little lateralizing value. DES elicited mostly motor phenomena, confirming previous studies, but no speech arrest. Of special interest was the SMA – middle cingulate cortex (MCC) relationship. Sleep seems to modulate SMA connectivity. The clinic- anatomic-electrographic correlations indicated a wide epileptogenic zone for resection, including SMA and MCC. Conclusions. The SMA is usually only a part of the frontal EZ, which usually includes the MCC other frontal mesial brain structures. Semiology of the seizures does not always provide lateralization cues and invasive exploration is needed for the delineation of the resection area. Connectivity of the SMA during wakefulness and sleep exhibits a complex relationships and further studies are needed. The SMA seems to be safe to remove on the long term.

Keywords

• supplementary motor area
• middle cingulate cortex
• direct electrical stimulation
• 50 hz stimulation
• spes
• sleep spes
• drug-resistant epilepsy
• seeg
• epilepsy surgery