EEG and surface‐electromyography correlate of tonic seizures in supplementary sensorimotor area epilepsy

Supplementary sensorimotor area (SSMA) epilepsy is characterized by focal or bilateral asymmetric tonic seizures, which can be difficult to lateralize.1, 2 Scalp-EEG may be obscured or without correlate. Hence, these seizures could be misdiagnosed as psychogenic or as a movement disorder.3 Careful analysis of interictal/ictal scalp-EEG in transverse bipolar montage, with surface-electromyography (sEMG), can help clarify the diagnosis. We report a 30-year-old man with left SSMA epilepsy and focal tonic seizures of legs (right > left), who was initially admitted for “tremors” (Video 1). Interictal EEG demonstrated periodic slow waves with initial positivity at Fz > F3~ Cz, followed by a negativity (~100 ms later) at FP1~FP2 (Figure 1). The ictal EEG demonstrated bifrontal rhythmical delta (Figure S1), evolving into periodic epileptiform discharges, time-locked to synchronous tonic sEMG bursts in right quadriceps femoris (RQF) and hamstrings (RBF) (Figure 2). As opposed to SSMA epilepsy, primary motor area epilepsy is more likely to present with focal clonic seizures.1 All authors contributed to the conception, data collection, analysis, and interpretation of the data in this report. Akshaya Rathin Sivaji drafted the manuscript. Marshall Kirsch, Rupin Singh, Guadalupe Fernandez-BacaVaca, and Neel Fotedar critically revised the manuscript for important intellectual content. Neel Fotedar provided overall supervision. All authors approved the final version and agreed to be accountable for all aspects of the work. We thank the EEG technologists at University Hospitals Cleveland Medical Center for their utmost dedication and compassion. And we sincerely thank our patients. None of the authors report any relevant conflicts of interest. The relevant clinical and EEG data are included in the manuscript. Data S1: Figure S1: Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. Test yourself Which of the following is the typical seizure semiology in SSMA epilepsy? What is the most likely localization of interictal and ictal epileptiform discharges on scalp-EEG in SSMA epilepsy? Which of the following sEMG characteristics is most likely present in focal tonic seizures related to SSMA epilepsy? Answers may be found in the Supporting information.