They present often as tonic eyelid opening with some changes in breathing coupled with pupillary dilation, urinary incontinence, increased heart rate, and flushing can occur.Nonconvulsive status epilepticus occurs in about 50% of patients. The seizures can cause sudden falling often leading to injury. These "drop attacks" are typically the first manifestation of LGS. The attacks are characterized by a single, generalized monoclonic jerk that precedes tonic contraction of axial muscles. EEG findings
Findings that strongly suggest LGS include consistent slow spike-wave (< 3 hertz [Hz]) on awake EEG. The complexes typically consist of a spike (duration < 70 milliseconds) or a sharp wave (70-200 milliseconds), followed first by a positive deep trough, then a negative wave (350-400 milliseconds). Not every wave is preceded by a spike. Bursts increase and decrease without clear onset and offset. Slow spike waves may occur during seizure or between seizures, or may occur in absence of any observable clinical changes which helps distinguish pattern from extended 3-Hz spike-wave discharges. Ocular abnormality
Ocular abnormalities affect around 90% of children. They can present as refractive error, strabismus, cortical visual impairment, and premature retinopathy. Causes
The disease pathophysiology is mostly unknown, but some evidence implicates cortical hyperexcitability occurring at critical periods of brain development.There are two types of LGS: idiopathic and secondary. The cause of the idiopathic subtype is unknown. Secondary LGS occurs when an identifiable underlying pathology is responsible. The most common type of LGS (70–78%) is secondary. These patients tend to have a worse prognosis than those with idiopathic LGS.
Lennox–Gastaut syndrome (LGS) is a complex, rare, and severe childhood-onset epilepsy. It is characterized by multiple and concurrent seizure types, cognitive dysfunction, and slow spike waves on electroencephalogram (EEG). Typically, it presents in children aged 3–5 years and can persist into adulthood. It has been associated with several gene mutations, perinatal injuries, congenital infections, brain tumors/malformations, and genetic disorders such as tuberous sclerosis and West syndrome. The prognosis for LGS is poor with a 5% mortality in childhood and persistent seizures into adulthood (80%–90%).LGS was named for neurologists William G. Lennox (Boston, USA) and Henri Gastaut (Marseille, France), who independently described the condition. The international LGS Awareness Day is  on November 1. Signs and symptoms
The symptoms vary and progress with age and are characterized by a triad of seizures, cognitive dysfunction, and EEG findings. The triad may not fully emerge until 1–2 years after first seizure episode. Seizures
The peak age of onset of seizures is typically between 3 and 5 years of age. The mainstay symptoms are seizures that are frequent – occurring daily and difficult to treat with antiseizure medications. An estimated 30% of patients with infantile spasms (West syndrome) have been reported to progress with LGS.The seizures are most commonly tonic seizures. They occur most frequently during non-REM sleep (90%). They initially last only a few seconds and are activated by sleep. The presentation can be subtle.