The clinical features of the Lennox–Gastaut syndrome (LGS) have been recognized for more than 200 years. The current definition of LGS by the International League Against Epilepsy (ILAE) classification is: "LGS manifests itself in children aged 1–8 years, but appears mainly in preschool-age children. The most common seizure types are tonic-axial, atonic, and absence seizures, but other types such as myoclonic, generalized tonic–clonic seizures (GTCS), or partial seizures are frequently associated with this syndrome. Seizure frequency is high, and status epilepticus is frequent (stuporous states with myoclonias, tonic, and atonic seizures). The electroencephalography (EEG) usually has abnormal background activity, slow spike-waves less than 3 Hz and, often, multifocal abnormalities. During sleep, bursts of fast rhythms (10 Hz) appear. In general, there is mental retardation. Seizures are difficult to control, and the development is unfavorable. In 60% of cases, the syndrome occurs in children suffering from a previous encephalopathy, but is primary in other cases."
A triad of basic elements for diagnosing LGS is typically based on this definition, and tailored by clinical experience and research:
Multiple types of seizures including tonic seizures, atypical absences, and atonic seizures
An EEG pattern consisting of interictal diffuse slow spike and wave discharges occurring at a 1.5–2 Hz frequency
Global cognitive dysfunction.
This is no consensus about the minimal necessary and sufficient criteria to diagnose LGS. Some investigators do not consider cognitive dysfunction indispensable for diagnosis, especially at onset, if the seizures and EEG pattern are typical. Others use stricter EEG criteria requiring that the diagnostic EEG pattern include bursts of generalized fast spikes (10 Hz) during nonrapid eye movement (NREM) sleep.
LGS accounts for 1%–4% of all cases of childhood epilepsy, but 10% of cases that start in the first 5 years of life. The annual incidence of LGS in childhood is 2 per 100,000 children while its prevalence ranges from 0.1 to 0.28 per 1000 in Europe and the United States. Males are affected more often than females but this gender difference is not statistically significant. There are no racial differences in the occurrence of LGS. The mean age at epilepsy onset is 26–28 months (range 1 day-14 years).
Patients are considered to have idiopathic LGS if there is normal psychomotor development before the onset of symptoms, if there are no underlying disorders or definite presumptive causes, and if there are no neurologic or neuroradiologic abnormalities. In contrast, patients have symptomatic LGS if there is an identifiable cause for the syndrome. Population-based studies reveal that 22%–30% of patients have idiopathic LGS, while 70%–78% have symptomatic LGS.
Pathologies responsible for LGS include encephalitis/meningitis, tuberous sclerosis, brain malformations (e.g., cortical dysplasias), birth injury, hypoxic–ischemic injury, frontal lobe lesions, and trauma. Infantile spasms precede the development of LGS in 9%–41% of cases. Some investigators consider cryptogenic cases in which there is no identified cause ...