Ictal MEG recordings constitute rare data. The objective of this study was to evaluate ictal magnetic source localization (MSI), using two algorithms: linearly constrained minimum variance (LCMV), a beamforming technique and equivalent current dipole (ECD). Ictal MSI was studied in six patients. Three of them were undergoing post-operative re-evaluation. For all patients, results were validated by the stereoelectroencephalographic (SEEG) definition of the epileptogenic zone (EZ). EZ was quantified using the epileptogenicity index (EI) method, which accounts for both the propensity of a brain area to generate rapid discharges and the time for this area to become involved in the seizure. EI values range from 0 (no epileptogenicity) to 1 (maximal epileptogenicity). Levels of concordance between ictal MSI and EZ were determined as follows: A: ictal MSI localized the site whose value EI = 1, B: MSI localized a part of the EZ (not corresponding to the maximal value of EI = 1), C: a region could be identified on ictal MSI but not on SEEG, D: a region could be identified on SEEG but not on MSI, E: different regions were localized on MSI and SEEG. Ictal MEG pattern consisted of rhythmic activities between 10 and 20 Hz for all patients. For LCMV (first maxima), levels of concordance were A (two cases), B (two cases) and E (two cases). For ECD fitted on each time point separately (location characterized by the best goodness-of-fit value), levels of concordance were A (one case), B (one case), D (three cases) and E (one case). For ECD calculated for the whole time window, levels of concordance were A (two cases) and D (four cases). Source localization methods performed on rhythmic patterns can localize the EZ as validated by SEEG. In terms of concordance, LCMV was superior to ECD. In some cases, LCMV allows extraction of several maxima that could reflect ictal dynamics. In a medial temporal lobe epilepsy case, ictal MSI indicated an area of delayed propagation and was non-contributory to the presurgical assessment.
Chronic lymphocytic inflammation with pontine perivascular enhancement re-sponsive to steroids (CLIPPERS) is an inflammatory disease of the CNS first described by Pittock et al in 2010 (1). Patients usually present with subacute ataxia, diplopia, and a range of other clinical features related to brainstem involvement. Brain magnetic resonance imaging (MRI) shows ''punctate'' and/or ''curvilinear'' gadolinium enhancement peppering the pons and extending variably into the brachium pontis, cerebellum, and adjacent CNS structures. An extensive laboratory, radiologic, and pathologic analysis is essential to exclude other diseases (2). Patients have favorable clinical and radiologic response to steroids requiring chronic immunosuppression (2); otherwise, without a specific treatment, progression seems to be relapsing-remitting (3). Lesion biopsies have revealed perivascular CD4-dominated T-cell or lymphohistiocytic infiltrates and activated microglia, involving predominantly the white matter (2). The pathogenesis and pathophysiology of CLIPPERS are unknown. Herein, we present the first case of CLIPPERS with FIGURE 1. Magnetic resonance imaging (MRI). Axial (A, B) and coronal (C) T2-weighted images show patchy areas of hyperintensity in the brainstem, middle cerebellar peduncles, and left deep cerebellar white matter. (D, E) After gadolinium injection, coronal T1-weighted images reveal multiple foci of linear and punctate enhancement peppering the brainstem, mainly at the pons, as well as in the left middle cerebellar peduncle and deep cerebellar white matter. (F) Two weeks after starting corticotherapy, follow-up MRI coronal T2 image shows a decrease in size and extent of lesions.
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