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In Reply: Forecasting Seizure Freedom After Epilepsy Surgery Assessing Concordance Between Noninvasive and StereoEEG Findings

2020; Lippincott Williams & Wilkins; Volume: 88; Issue: 3 Linguagem: Inglês

10.1093/neuros/nyaa503

1524-4040

Reinaldo Uribe-San-Martín, Roberta Di Giacomo, Roberto Mai, Francesca Gozzo, Veronica Pelliccia, Valeria Mariani, Francesco Cardinale, Ethel Ciampi, Marco Onofrj, Laura Tassi,

Functional Brain Connectivity Studies

To the Editor: We really thank Yue and Yang1 for their high interest in our recent paper on the concordance at a sublobar localization derived from noninvasive studies (video electroencephalography [video-EEG], magnetic resonance imaging [MRI], and [18F]fluorodeoxyglucose positron emission tomography [FDG-PET]) and the probable epileptogenic zone (EZ) as defined by the gold-standard stereoEEG.2 As in any scientific article, there can be many points for discussion. Stereoelectroencephalography (SEEG)-guided radiofrequency thermocoagulation (THC) was recently demonstrated as an excellent therapeutic tool in a wide range of histopathologies in focal drug-resistant epilepsies, but especially in periventricular nodular heterotopia (PNH). PNH demonstrates widespread structural and functional alterations with differential interactions between the overlying cortex and nodules, with a peculiar and individually defined pattern of seizure initiation and propagation.3 Only by exploiting the data of the SEEG, a correct THC strategy including the nodules but also the close or sometimes distant cortex, allowed the correct identification of the amount of tissue to be coagulated.4-6 However, concerning the absence of seizure-free patients after THC in our work, the strict inclusion criterion was the mandatory surgery once refractory epilepsy was confirmed after THC failure. We analyzed the differences in the time from THC to seizure recurrence (warranting resective surgery), and no statistically significant findings were observed (Table, Supplemental Digital Content 82; comparing postsurgical outcomes according to the time from THC to seizure relapse and time from THC to resection). Patients who achieved complete remission after THC alone were therefore not included in the present study. In our center, SEEG is considered the gold-standard procedure in order to better define the location and extension of the EZ, and PET is still considered as an ancillary procedure, unable to define the EZ correctly by itself. SEEG data are considered to be prevalent and sufficient. SEEG is planned after a careful examination of noninvasive studies; differences betweenstudies can only be observed after SEEG is complete. When inconsistencies between invasive and noninvasive examinations were observed, a cautious decision for surgical resection was made, taking into account mainly imaging findings and seizure-onset zone. Furthermore, in the possible event of discrepancies between the methodologies, the healing percentages provided to the patient are obviously lower. But still, the greatest and insurmountable gap between noninvasive (positron emission tomography [PET], single-photon emission computed tomography [SPECT], and high-density EEG [HD-EEG]) methodologies, invasive (electrocorticography [ECoG]) methodologies, and SEEG is the different timing in which they occur. Considering that in the literature it has not yet been proven that the definition of EZ can be based only and exclusively on any recording of the neurophysiological, metabolic, or network state, depriving itself of the recording of seizures, it seems to us that the SEEG or invasive recordings, when necessary, remain the gold standard. Of course, the ECoG is also able to provide very useful information, but only in the intercritical condition. In most histopathological groups, a weak correlation was observed between interictal abnormalities (within both the lesional and the irritative zones) and EZ, with the exception of focal cortical dysplasia (FCD) type IIa and IIb.7,8 In our practice, intraoperative ECoG is not used, but it may represent a useful tool providing additional neurophysiological information in selected patients. Thanks again for the question regarding antiepileptic drug (AED) management after surgery. We exploit this opportunity to analyze some supplemental details in our own work regarding AEDs. Approach to drug withdrawal after surgery is still a matter of debate.9,10 In our study, 45 (61%) patients took unchanged therapy, 24 (32%) patients were reducing therapy, and 5 (7%) patients completely discontinued therapy. Of the 46 patients in Engel's class I, 24 (52%) were receiving therapy reduction and 4 (9%) patients were no longer taking AEDs. Usually, withdrawal of AEDs was slowly performed only after 12 mo of seizure freedom in patients in class I, so with a mean follow-up of 2.8 + 2.4 yr after surgery, our total discontinuation results were still premature. And, finally, we acknowledge the advice of Yue and Yang1 to analyze what type of etiology most often leads to inconsistencies between invasive and noninvasive examinations. We performed an exploratory univariate post hoc analysis comparing different etiologies (histopathologies) assessing concordance between noninvasive and SEEG probable epileptogenic zones. We observed that in polymicrogyria a greater proportion of patients (3/4 vs 5/70, P = .003) had a larger EZ observed in MRI compared to the probable EZ demonstrated by the SEEG. Similarly, we found few patients with negative MRI in scar (0/5 vs 42/69, P = .013), hippocampal sclerosis (1/4 vs 41/67, P = .038), and polymicrogyria (0/4 vs 42/70, P = .031). Funding This study did not receive any funding or financial support. Disclosures The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.