De novo late-onset absence status epilepticus or late-onset idiopathic generalized epilepsy? A case report and systematic review of the literature.

Idiopathic (genetic) generalized epilepsies (IGEs) are age-related epileptic syndromes with typical age onset in childhood or adolescence. We report a patient with de novo late-onset absence status epilepticus (ASE) occurring at the age of 64 years, with clinical and EEG features suggestive of late-onset IGE. We also discuss the relationship between de novo late-onset ASE and late-onset IGE, and provide a comprehensive and critical review of the available literature on late-onset (i.e. onset ≥60 years) IGE. MEDLINE (1966-2016 [23th April]) was systematically searched in order to identify reports of patients with late-onset IGE. Grey literature was also comprehensively searched. We identified nine patients with electroclinical features suggestive of late-onset IGE. Median age at seizure onset was 71 years (range: 60-80), with a female prevalence (67%). A family history of epilepsy was reported in 67% of cases. All patients had generalized tonic-clonic seizures, and 44% also had myoclonic seizures. Treatment and outcome were reported for six patients; all of whom reached seizure freedom under monotherapy with valproic acid (83%) or lamotrigine (17%) (range of follow-up: 3 to 24 months). Late-onset IGE are entities with unknown prevalence and incidence, and should be differentiated on the basis of late-onset reactivation of previous IGE. Late-onset IGEs are probably unrecognized or misdiagnosed, based on a common misconception that all elderly individuals with first-ever seizures have focal symptomatic epilepsy. Late-onset IGE should be actively investigated by accurate history taking aimed at identifying seizures, which may have been unnoticed, and familial antecedents of epilepsy. In elderly patients presenting with de novo late-onset ASE, a diagnosis of late-onset IGE should be considered in the differential diagnosis, particularly in atypical cases (e.g. absence of triggering factors, coexistence of generalized tonic-clonic or myoclonic seizures, and interictal generalized epileptiform discharges).