Diagnosing LGS

Lennox-Gastaut syndrome (LGS) is a type of epilepsy that usually develops before the age of 7.1 It occurs more often in boys than girls. It is very rare—LGS only accounts for between 1% to 4% of all childhood epilepsy cases.1

LGS is usually characterized by2:

  • Multiple seizure types
  • An EEG A test for diagnosing epilepsy. The EEG records electrical activity in the brain. Small, metal disks are attached to the scalp and connected by wires to an EEG machine. The machine records brain activity as a series of lines, each related to a different part of the brain. with a slow spike-wave pattern between seizures
  • Cognitive impairment or developmental delays

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Understanding the EEG

Understanding the EEG

Electroencephalography (EEG) records the electrical activity of the brain. It is an important test for diagnosing epilepsy because it shows patterns of normal or abnormal brain activity.3

When diagnosing LGS, doctors will look for diffused slow spikes and slow waves of 2-2.5 cycles per second.4 This is between seizures, and while the person is awake.4 An EEG during sleep is also necessary. Bursts of diffuse or bilateral fast rhythm patterns (10 cycles/second) or "polyspikes," also called generalized paroxysmal fast activity, are recorded during sleep.4

These EEG patterns help differentiate LGS from other epilepsy syndromes.4

Cause of LGS

Causes of LGS

The history and causes of LGS vary. An estimated 20% of children with LGS have a prior history of infantile spasms Also known as West syndrome, these seizures start in children between 3 and 12 months old and may potentially be controlled with treatment. They begin with a sudden jerk and muscle stiffening. Often the arms are stretched out and the knees pull up. Seizures often occur in a series. (often referred to as West syndrome).4 LGS can be caused by genetic disorders such as tuberous sclerosis.1

Injuries affecting the brain, such as lack of oxygen or diseases like meningitis and encephalitis, can also cause LGS when they happen within a few months of birth.1 Unfortunately, a cause cannot be found for roughly 1 in 3 cases.1



Once a child is diagnosed with LGS, the prognosis varies by individual. The cause associated with the syndrome will likely affect the prognosis, and sometimes the therapeutic strategies. Some factors that may affect the prognosis include a prior history of infantile spasms.5

Learn why it is difficult to diagnose LGS

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LGS is a type of epilepsy that affects a child’s intellectual functioning and may cause behavioral disturbances.6 Unfortunately, LGS usually persists through childhood and adolescence into adulthood. Unfortunately, there is no cure for LGS, so freedom from seizures and normal development is very unusual.6

While the seizures associated with LGS are difficult to control, there are treatment options that may help.6 It is important for parents and caregivers to understand the different types of seizures associated with LGS. By keeping track of seizure activity and frequency in daily life, parents can give doctors information that may help improve the treatment plan.7


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  • 1. Crumrine PK. Lennox-Gastaut syndrome. J Child Neurol. 2002;17(suppl 1):S70-75.
  • 2. Shafer PO, Kiriakopoulos E, Sirven JI. LGS: characteristics. Epilepsy Foundation Web site. https://www.epilepsy.com/learn/types-epilepsy-syndromes/lennox-gastaut-syndrome-lgs/lgs-characteristics. Updated November 2014. Accessed November 27, 2019.
  • 3. Schachter SC, Sirven JI. EEG. Epilepsy Foundation Web site. http://www.epilepsy.com/learn/diagnosis/eeg. Updated August 22, 2013. Accessed December 1, 2019.
  • 4. Arzimanoglou A, French J, Blume WT, et al. Lennox-Gastaut syndrome: a consensus approach on diagnosis, assessment, management, and trial methodology. Lancet Neurol. 2009;8:82-93.
  • 5. Shafer PO, Kiriakopoulos E. LGS: causes. Epilepsy Foundation Web site. https://www.epilepsy.com/learn/types-epilepsy-syndromes/lennox-gastaut-syndrome-lgs/lgs-causes. Published November 2014. Accessed December 1, 2019.
  • 6. NINDS Lennox-Gastaut syndrome information page. National Institute of Neurological Disorders and Stroke Web site. https://www.ninds.nih.gov/Disorders/All-Disorders/Lennox-Gastaut-Syndrome-Information-Page. Updated March 27, 2019. Accessed October 21, 2019.
  • 7. Phillips L. Dear seizure diary: how and why to record your epileptic seizures. Neurology Now. 2009;5(6):35-36.