LETTERTOTHEEDITOR Seizure freedom after intracranial electrode implantation in pharmacoresistant epilepsy V.-H. Nguyen-Michel a , S. Dupont a,b,c,d , L. Thivard b , B. Mathon c,d,e , V. Lambrecq a,c , D. Hasboun c,f , V. Navarro a,c,d , M.-O. Habert c,d,g , S. Clemenceau e , M. Baulac a and C. Adam a a Epileptology Unit, AP-HP, H^ opital La Piti e-Salp^ etri ere, Paris, b Rehabilitation Unit, AP-HP, H^ opital La Piti e-Sal- p^ etri ere, Paris, c Sorbonne Universit es, UPMC Universit e Paris 06, Paris, d ICM-IHU, INSERM, CNRS, Paris, e Neurosurgery Unit, AP-HP, H^ opital La Piti e-Salp^ etri ere, Paris, f Neuroradiology Unit, AP-HP, H^ opital La Piti e-Sal- p^ etri ere, Paris, and g Nuclear Medicine Department, AP-HP, H^ opital La Piti e- Salp^ etri ere, Paris, France Correspondence: C. Adam, Epileptology Unit, H^ opital La Piti e-Salp^ etri  ere, 47-83 Boulevard de L’H^ opital 75013, Paris, France (tel.: +33142161831; fax: +33144245247; e-mail: claude.adam@aphp.fr). Keywords: electrodes, epilepsy, intracranial, seizure freedom, surgery doi:10.1111/ene.13487 Received: 19 June 2017 Accepted: 16 October 2017 Case 1 A 33-year-old man had experienced sev- eral seizures per month (partial or gen- eralized) since childhood despite multiple antiepileptic drug (AED) polytherapies. Video-electroencephalography, fluoro- deoxyglucose-positron emission tomogra- phy and subtraction ictal-interictal single photon emission computed tomography coregistered with magnetic resonance imaging led to the diagnosis of magnetic resonance imaging-negative left temporal lobe (TL) epilepsy. He underwent video- intracranial electroencephalography with nine electrodes implanted in the left TL (Fig. 1a and c; Data S1). Three seizures were recorded, characterized by fear and gestural/oral automatisms, and some- times right-sided clonic jerks and gener- alization. Ictal discharges originated in the left temporal pole, spread to the hippocampus and then other brain regions (Fig. S1). A left temporal polar resection was contemplated but not per- formed, as seizures did not recur after electrode removal and at follow-up of 4 years, despite AED reduction. Case 2 A 37-year-old man had developed daily focal seizures refractory to AED poly- therapies since the age of 8 years. Video-electroencephalography, magnetic resonance imaging and fluorodeoxyglu- cose-positron emission tomography indi- cated non-lesional bilateral TL epilepsy. He underwent video-intracranial elec- troencephalography with Spencer elec- trodes and subdural strips to explore both TLs (Fig. 1b). Six seizures were recorded, one asymptomatic and the others with gestural/oral automatisms and moaning. Fast ictal discharges emerged from the left amygdalar-hippo- campal-entorhinal cortex, sometimes accompanied by slow rhythmic spikes and waves in the right hippocampus, and bilateral fast development (Fig. S2). Interictal spikes were abundant in the right hippocampus. Surgery was post- poned because of uncertain outcome. Unexpectedly, seizures did not recur over a period of 14 years after electrode removal, despite AED reduction. The patients gave informed consent for participation. No ethics board approval was needed because it was a retrospective case report based on medical records. Discussion Our cases were drawn from a series of 163 implanted patients [1]. Remarkably, implantation was followed by a pro- longed, complete remission of epileptic seizures that could not be traced to surgi- cal complications or changes in AED. The minimal perturbation due to intracranial electrodes evidently some- times has strong effects on human epilep- tic networks. Unlike stereotaxic electroencephalogra- phy-guided radiofrequency thermocoagu- lation [2], our procedures do not intentionally damage targeted cortical sites, although small brain lesions are likely. In our first case, intracerebral elec- trode trajectories frequently crossed white matter potentially disturbing sei- zure propagation pathways. In the sec- ond case, only Spencer electrodes were intracerebral and their trajectory was mostly intrahippocampal through the long axis of the hippocampi. These elec- trodes are relatively small (1 mm). Pre- sumably they cause little disruption of lamellar or non-lamellar hippocampal functions [3] and cannot cut the longitu- dinal fibers as do multiple hippocampal transections [4]. Effects may have resulted instead from the destruction of a very local hippocampal focus. An implantation effect might also occur in chronic hippocampal stimulation for sev- ere epilepsy [5]. Acknowledgements We would like to thank Richard Miles for critical reading of the manuscript. Disclosure of conflicts of interest M.-O.H. has received honoraria as a speaker from Lilly, GE Healthcare and Piramal. The other authors declare no financial or other conflicts of interest. Supporting Information Additional Supporting Information may be found in the online version of this article: Figure S1. Intracranial electroencephalog- raphy data in Patient 1. Figure S2. Intracranial electroencephalog- raphy data in Patient 2. Data S1. Legend of Fig. 1c (describing the traces left by electrodes on patient 1’s magnetic resonance imaging). EUROPEANJOURNALOFNEUROLOGY LETTERTOTHEEDITOR © 2017 EAN e7