Idiopathic generalised epilepsy of adult onset: clinical syndromes and genetics.

OBJECTIVE: To study the clinical features and genetics of idiopathic generalised epilepsy (IGE) beginning in adult life.
METHODS: Consecutive patients with IGE, defined as generalised seizures with spike or polyspike and wave on EEG, were studied in the setting of a first seizure clinic where an early postictal EEG record is part of the protocol. Patients were divided into two groups: "classical IGE" with onset before 20 years and inclusive of all the IGE subsyndromes recognised by the international classification; and "adult onset IGE", when seizure onset was at age 20 years or later. Seizure patterns, clinical features, and genetics of the adult onset group were examined.
RESULTS: Of 121 patients with an electro-clinical diagnosis of IGE, 34 (28%) were diagnosed as adult onset IGE. The seizure patterns in these 34 cases were tonic-clonic seizures + absences (3), tonic-clonic seizures + myoclonus (6), and tonic-clonic seizures alone (25). Tonic-clonic seizures were often precipitated by alcohol or sleep deprivation. The proportion of affected first and second degree relatives did not differ between the classical and adult onset IGE groups. Twenty adult onset cases were treated with sodium valproate, four with other antiepileptic drugs, and 10 were untreated. Follow up of 32 of the 34 cases (for 31 (22) months (mean (SD)) showed that tonic-clonic seizures recurred in eight patients: five with identified provocative factors and three without.
CONCLUSIONS: Adult onset IGE is a relatively frequent and benign disorder. Seizures are usually provoked and are easy to control. Patients in this age group may often be misdiagnosed as having non-lesional partial epilepsy. Early postictal EEG and sleep deprivation studies may improve the detection of these patients. Pedigree analysis suggests that adult onset IGE, like classical IGE, has a genetic aetiology.