For a child or adult to be diagnosed with LGS, three key features must be present. These include:
- Multiple seizure types: including tonic, atonic or drop attacks, atypical absence, myoclonic, and generalized tonic-clonic seizures starting in childhood. Seizures begin in childhood but different types may emerge over time.
- A characteristic EEG pattern: In a person with LGS the background activity on EEG is slow and this abnormality can be seen all the time or it can come and go. The EEG also shows slow spike and wave epileptiform activity when the person is awake. These bursts of electrical activity are seen frequently over the course of a day, sometimes more frequent than others.
- During non-REM sleep, epileptiform discharges are more generalized and more frequent. They include many spikes and slow wave features.
- During REM sleep, spike and wave activity is less. Periods of fast activity are also seen during sleep (in either REM or non-REM parts of sleep).
EEG changes during seizures in LGS may show seizure activity in certain areas of the brain, generalized discharges, as well as brain waves that are slower and more irregular than normal throughout the brain or in just parts of the brain.
Cognitive impairment, behavior problems or developmental delay: Before the seizures begin, 20 to 30% of children with LGS do not show any neurological or developmental problems. However over the years, these problems almost always appear and often get progressively worse as the person gets older. Cognitive function is in the normal range for 10 to 20% of children with LGS. Yet, they may have slower thinking or processing which can affect their daily function.
The changes in thinking and behavior are often due to the underlying disturbance in brain function. Frequent seizures also interfere with how the brain works and a person’s thinking and behavior can vary with the number and severity of seizures. Side effects of medicines may also affect how a person functions. Usually people with LGS need two or more seizure medicines to combat the multiple seizure types, which unfortunately increases the risks of side effects.