Origin coordinate influence on performance of temporally extended signal space separation in magnetoencephalography.

OBJECTIVE: Temporally extended signal space separation (tSSS) is a powerful method for artifact suppression in magnetoencephalography (MEG). Because tSSS first separates MEG signals coming from inside and outside a certain sphere, definition of the sphere origin is important. For this study, we explored the influence of origin choice on tSSS performance in spontaneous and evoked activity from epilepsy patients. METHODS: Interictal epileptiform discharges (IEDs) and somatosensory evoked fields (SEFs) were processed with two tSSSs: one with the default origin of (0, 0, 40 mm) in the head coordinate, and the other with an individual origin estimated using each patient's anatomical magnetic resonance imaging (MRI). Equivalent current dipoles (ECDs) were calculated for the data. The ECD location and quality of estimation were compared across conditions. RESULTS: MEG data from 21 patients revealed marginal differences in ECD location, but the estimation quality inferred from goodness of fit (GOF) and confidence volume (CV) was better for the tSSS with individual origins. This choice affected IEDs more than it affected SEFs. CONCLUSIONS: Individual sphere model resulted in better GOF and CV. SIGNIFICANCE: Application of tSSS using an individual origin would be more desirable when available. This parameter might influence spontaneous activity more strongly.

Long-Term Undiagnosed Nonconvulsive Status Epilepticus Identified by Urgent Electroencephalography with Hyperventilation Activation.

Nonconvulsive status epilepticus (NCSE) might be underdiagnosed in cases where clinical symptoms are ambiguous. If a patient exhibits ictal psychiatric symptoms such as NCSE presentation and is misdiagnosed as having a psychiatric disorder, the patient may be treated in psychiatry settings, where continuous electroencephalography (cEEG), the gold standard for NCSE diagnosis, is typically not used. Herein, we report our experience with a patient having NCSE who exhibited psychiatric symptoms and remained misdiagnosed for many years. We also included a brief review of the relevant literature. Our experience with this patient presents two clinically significant points: (1) clinicians should consider NCSE in the differential diagnosis of interictal psychosis when patients with epilepsy, in whom the seizure type is unknown, repeatedly present transient psychiatric symptoms, and (2) urgent EEG with hyperventilation activation during acute periods may help diagnose patients with suspected NCSE.