This syndrome is characterized by the presence multiple types of intractable seizures (in particular tonic seizures in sleep, but atonic and atypical absence seizures also occur), cognitive and behavioral impairments and diffuse slow spike-and-wave and paroxysms of fast activity on EEG.
NOTE Lennox Gastaut syndrome is considered an 'epileptic encephalopathy'. This term denotes the concept that the epileptic activity itself might directly contribute additional cognitive and behavioral impairments over those expected from the underlying etiology alone, and that suppression of epileptic activity might minimize this additional impairment.
This syndrome is characterized by onset of seizures from age 1 to 7 years (peak 3 to 5 years). Both sexes are affected. Antecedent, birth and neonatal history may be normal or there may be a history related to a structural brain abnormality (developmental or acquired). Neurological exam and head circumference may be normal or may reflect underlying structural brain abnormality. Development and cognition prior to presentation is usually abnormal, but occasionally onset may occur in an otherwise normally developing child. Subsequent developmental stagnation or regression is typical after the onset of seizures.
Around 10-30% of cases of Lennox Gastaut syndrome evolve from earlier onset epilepsies, including West and Ohtahara syndromes. Occasionally there is a history of previous febrile seizures, focal seizures or generalized seizures.