Lennox–Gastaut syndrome

Lennox–Gastaut syndrome (LGS) is a rare and severe form of childhood-onset epilepsy. It involves multiple seizure types occurring together, including tonic seizures, cognitive impairment, and a distinctive pattern of slow spike-wave activity on an electroencephalogram (EEG). The condition typically begins in children between three and five years old and usually continues into adulthood, though the electrical and clinical features may shift slightly over time. The syndrome is named after American neurologist William G. Lennox and French neurologist Henri Gastaut, who each described it independently. International LGS Awareness Day is observed on November 1.

Signs and symptoms vary and evolve with age. The core features are a triad of seizures, cognitive dysfunction, and abnormal EEG findings, though this triad may not fully appear until one to two years after the first seizure.

Seizures often start in the first year of life, with the full syndrome emerging between ages three and five. Seizures are frequent—occurring daily—and are hard to control with medication. About 30% of children with infantile epileptic spasm syndrome (formerly West syndrome) go on to develop LGS. Tonic seizures are the most common type and affect nearly everyone with the condition. They happen most often during non-REM sleep (about 90% of the time), last less than a minute, and can be subtle—such as tonic eyelid opening with changes in breathing, dilated pupils, loss of bladder control, increased heart rate, or flushing. Nonconvulsive status epilepticus occurs in roughly half of patients. Sudden falls, known as drop attacks, are often the first sign of LGS and can cause injury. These attacks involve a single myoclonic jerk followed by a stiffening of the trunk muscles.

On an awake EEG, LGS is strongly suggested by consistent slow spike-wave activity at less than 3 hertz. These complexes usually consist of a spike (under 70 milliseconds) or sharp wave (70–200 milliseconds), followed by a deep positive trough and then a negative wave (350–400 milliseconds). Not every wave has a preceding spike. Bursts of activity increase and decrease without clear start or end points. Slow spike waves can appear during seizures, between seizures, or without any observable clinical change, which helps distinguish LGS from the pattern of extended 3-Hz spike-wave discharges.