Nonconvulsive status epilepticus - A possible cause of mental retardation in patients with Lennox-Gastaut syndrome

Lennox-Gastaut syndrome (LGS) is one of the most severe types of childhood epilepsy. It is usually resistant to treatment and associated with mental r etardation. To delineate the risk factors associated with the outcome of LG S, we evaluated, in a retrospective and multicentre study, the course of th e disease, EEG tracings, and intellectual function in 101 patients. Inclusi on criteria were the presence of tonic seizures as well as slow spike and w ave complexes in the EEG. The average documented observation period was 16 years (range 4-31 years). Overall, the intellectual and neurological outcom e was poor. At the last follow-up, 38% of the patients could not speak, 21% were unable to walk and only 4% were free of seizures. Four independent ri sk factors for severe mental retardation were identified by multivariate an alysis. These were in a decreasing order of importance: nonconvulsive statu s epilepticus (NCSE), odds ratio (OR) 25.2, a previous diagnosis of West sy ndrome (OR 11.6), a symptomatic etiology of epilepsy (OR 9.5), and an early age at onset of epilepsy (OR 4.7). The results highlight the association b etween NCSE and the severity of mental retardation in patients with LGS; th is association appears to be independent of symptomatic etiology. Our data provide an indirect evidence that, at least in some of the patients, NCSE i s not only a concomitant feature, but also a cause of severe mental retarda tion.