Supplementary Motor Area Epilepsy: From Semiology to Electrophysiology

Abstract

Introduction: The objective of supplementary motor area (SMA) epilepsy surgery is complete resection or disconnection of epileptogenic zone while sustaining the functionally relevant eloquent cortex. Various diagnostic modalities are used to define the seizure onset zone and eloquent cortex. However, SMA epilepsy remains diagnostic challenge due to its location is concealed in mesial frontal lobe. The clinical characteristics of SMA epilepsy has been described as an abrupt tonic posturing one or more extremities, vocalization, without loss of consciousness. Nonetheless, due to preservation of consciousness, SMA epilepsy can be mistakenly diagnosed. Moreover, electrophysiological findings are also often misleading because of interictal spikes found in the midline have normal background rhythm and paradoxical lateralization. On the other hand, MEG as the latest neurophysiological tools, has great spatial resolution and high signal-to-noise ratio which offers several advantages over EEG in detecting epileptogenic foci in SMA epilepsy. Therefore in this study, we reevaluate presurgical diagnostic modalities and sought to find clinical value of MEG to localize epileptogenic zone in SMA epilepsy. Moreover, lateralizing value of semiology observed in patient group will also be determined.

Methods: Forty-four patients who underwent epilepsy respective surgery and had SMA removed were reviewed retrospectively. Clinical characteristics of each patients were assessed and its lateralizing value were calculated. Concordance of interictal VEM, PET, ictal SPECT, and MRI results to resection area were evaluated and related them to surgical outcome. Interictal spikes source ii distribution in simultaneous EEG/MEG were done by using sLORETA separately to compare EEG and MEG sensitivity.

Results: The most reliable predictors of seizure lateralization were versive head movement and unilateral tonic posturing (p=0.004 and p=0.021, respectively), indicating contralateral lateralization in more than 90% of patients. Only interictal MEG significantly localized correctly in 7 of 9 patients with favorable outcome (p=0.021) and none of the non-favorable outcome patients showed abnormalities localized in epileptogenic lobe. In simultaneous EEG/MEG, 4 of 7 favorable outcome patients showed non-lateralizing interictal EEG, while 6 of 7 favorable outcome patients showed localized interictal MEG within resection area. One patient had MRI revealed tumor lesion in right SMA and also left hippocampal sclerosis, exclusively had interictal EEG spikes that constantly located in temporal lobe while interictal MEG spikes predominantly localized within resection area. Conclusion: MEG is a useful tool in localizing epileptogenic zone, especially when EEG fails to localize or lateralize epileptogenic lesion in the midline area, such in SMA epilepsy case. Keyword: Supplementary motor area (SMA), Epilepsy, Electroencephalography (EEG), Magnetoencephalography (MEG), Semiology, Electrophysiology Student Number: 2014-25244