Photosensitive tonic-clonic seizures:a continuum between focal and generalized seizures

Abstract

To investigate whether the tonic-clonic seizure (TCS) induced by intermittent photic stimulation (IPS)was generalized tonic-clonic seizure (GTCS)or partial secondarily tonic-clonic seizure (PGTCS),and to analyze the relationship between them. Video-electroencephalogram (VEEG)database of Peking University First Hospital from March 2010 to October 2018 were reviewed. Fifteen cases with idiopathic epilepsy who had TCS induced by IPS were included in this study, and their clinical and electroencephalogram (EEG)characteristics were retrospectively analyzed. In this study, 4 of the 15 cases were boys and 11 were girls. The age of seizure onset ranged from 1 to 13 years. According to the medical records: 12 cases were considered as GTCS,while the remaining 3 cases were considered as PGTCS. The age at VEEG monitoring ranged from 2.5 to 16.0 years. All backgrounds of the VEEG were normal. Interictal discharges:generalized discharges in 11 cases, of which 4 cases coexisted with posterior discharges, 2 cases coexisted with Rolandic discharges, the other 5 cases merely had generalized discharges; merely focal discharges in two cases, one in the Rolandic area and the other in the posterior area; no interictal discharge in the remaining 2 cases. IPS induced photoparoxysmal response (PPR)results: 2 cases without PPR,the remaining 13 cases with PPR of generalized discharges, and 6 of the 13 cases coexisted with posterior discharges. IPS induced photoconvulsive response (PCR)results: GTCS in one case (contradictory to medical history),PGTCS in 11 cases (consistent with medical history),and GTCS and PGTCS hardly to distinguish in the remaining 3 cases. Of the three conditions above, there were generalized myoclonic seizures induced by IPS before TCS in 7 cases. The medical history was unreliable in determining whether TCS was generalized or focal. Myoclonic seizures can coexist with PGTCS, and sometimes GTCS was indistinguishable from PGTCS, indicating that the dichotomy of seizure types need to be improved. Photosensitive TCS should be regarded as a continuum between focal and generalized seizures.