Abstracts

Rationale: Lennox-Gastaut syndrome (LGS) denotes a refractory epileptic encephalopathy with the classic triad of generalized slow spike-wave on inter-ictal EEG, multiple seizure types and intellectual impairment. The epileptogenic processes associated with LGS have been postulated to sustain abnormal patterns of brain activity and connectivity, which in addition to recurrent seizures impair normal developmental mechanisms leading to subsequent impairment of cognition(Blume WT. Men Ret Dev Dis 10:150-3 (2004)). Cognitive outcomes in LGS can depend on age of onset, predominance of certain seizure types and interictal background activity. Earlier age of onset, higher frequency of tonic seizures, repeated episodes of nonconvulsive status, and constantly slow interictal background have poor cognitive outcomes (Goldsmith IL et al. Epilepsia 41:395-9 (2000)). When diagnosed in later life, LGS may have a better cognitive outcomes. We describe factors associated with normal cognitive functioning in five patients from our practice with electro-clinical findings consistent with LGS.  Methods: Patients fulfilling the semiological and EEG characteristics of LGS but without cognitive impairment were identified from GPK’s personal practice retrospectively over the 10-year period from 2006-16. Data collected included age, sex, age of seizure onset, EEG characteristics, MRI findings, behavioral co-morbidities and results from cognitive neuropsychological testing. Results: Five patients were identified (3 female, 2 male; Table 1). The mean age at seizure onset was 13.8±2.5 years. All patients had multiple seizure types including generalized tonic-clonic, atonic and atypical absence. High-resolution brain MRI was normal in all patients. Inter-ictal EEG showed generalized slow spike-wave complexes and generalized paroxysmal polyspike activity in all patients. Posterior background rhythms were within the normal alpha range (8-13 Hz) in all patients. One patient completed high school, two patients had obtained college degrees, one patient completed three years and another completed two years of college. Mean intelligent quotient (IQ) on neuropsychology testing was 86.6±14.0; individual IQ scores in three patients was >90. All patients were able to perform their activities of daily living independently. Conclusions: LGS is a composite electro-clinical syndrome that may be the common expressive pathway for a variety of etiologies (Edoarado et al. Ep Res 89:271-7 (2010)).The mechanism by which epilepsy attains its characteristic features in LGS remains unknown. We observed that in a small proportion of patients the disease process of LGS may spare cognition while still causing the syndromic epilepsy phenotype. Noteworthy features of our ‘high-functioning’ LGS cohort were seizure onset in the second decade and the presence of normal EEG background rhythms. Favorable cognitive outcome in LGS may relate to the brain progressing beyond a critical developmental stage for higher cognitive function prior to the onset of seizures Funding: N/A