Diagnosing LGS | About Lennox-Gastaut Syndrome (LGS)

Lennox-Gastaut syndrome (LGS) is a type of epilepsy that usually appears before the age of 8.¹ It most often appears in children between 3 and 5 years of age.¹ It is very rare—as few as 1%-4% of childhood epilepsies are classified as LGS.²

Even if your child is diagnosed early with epilepsy, it may take more time to diagnose LGS. Some of the features of LGS occur with other seizure conditions, which makes diagnosing LGS difficult. It is likely that you will need to go to a specialized epilepsy center to get a proper diagnosis by an epileptologist. There are three characteristics of LGS that, when taken together, differentiate it from other forms of epilepsy:

Multiple seizure types, including drop attacks (tonic or atonic), atypical absence, myoclonic, and generalized tonic-clonic seizures starting in childhood.
A specific type of EEG (electroencephalography) pattern called slow spike-wave, seen between seizures.
Cognitive impairment or developmental delay seen over time.³

Diagnosis of LGS is challenging.

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 in cycles of 2-2.5 per second.¹ This is between seizures, and while the person is awake.¹ The EEG during sleep is also necessary.¹ These EEG patterns differentiate LGS from other epilepsy syndromes.¹

Causes of LGS
The signs and causes of LGS vary. An estimated 20% of children with LGS have a prior history of infantile spasms. (often referred to as West syndrome).¹ LGS can be caused by genetic disorders such as tuberous sclerosis.² 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.² Unfortunately, a cause cannot be found for roughly 1 in 3 cases.²

Prognosis
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. Patients with a prior history of infantile spasms have a significantly worse prognosis.⁴

Risk factors for a less favorable LGS prognosis include:

Symptomatic cause
Prior history of infantile spasms
Onset before the age of 3
High frequency of seizures
Worsening periods of long duration
Repeated episodes of status epilepticus⁵

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. The types of seizures may change as the child gets older, but 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.⁵ It is important for parents and caregivers to understand the different types of seizures associated with LGS. By noting the type of seizures, when they happen, and how often, parents can give doctors information that may help improve the treatment plan.⁷

Learn more: Seizures associated with LGS »

References:
^1.	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.
^2.	Crumrine PK. Lennox-Gastaut syndrome. J Child Neurol. 2002;17(suppl 1):S70-75.
^3.	Wheless J. Lennox-Gastaut syndrome: characteristics and clinical manifestations. Epilepsy.com. http://www.epilepsy.com/epilepsy/epilepsy_LGS/characteristics. August 7, 2009. Accessed September 23, 2010.
^4.	Etiology/causes. Epilepsy.com. http://www.epilepsy.com/epilepsy/epilepsy_LGS/etiology. Accessed October 18, 2010.
^5.	Epilepsy syndromes. Epilepsy Foundation Web site. http://www.epilepsyfoundation.org/about/types/syndromes/lg.cfm. Accessed September 23, 2010.
^6.	NINDS Lennox-Gastaut information page. National Institute of Neurological Disorders and Stroke Web site. http://www.ninds.nih.gov/disorders/lennoxgastautsyndrome/lennoxgastautsyndrome.htm Updated June 15, 2010. Accessed September 23, 2010.
^7.	Phillips L. Dear seizure diary: how and why to record your epileptic seizures. Neurology Now. November/December 2009;5(6):35-36.