How is LGS Diagnosed?

A diagnosis of Lennox-Gastaut Syndrome is usually based upon a thorough clinical evaluation, a detailed patient history, and a complete physical and neurological evaluation, including advanced imaging techniques, such as electroencephalography (EEG) and magnetic resonance imaging (MRI).

Your doctor will look for these signs to diagnose LGS:

  • Seizures that started in early life
  • More than one kind of seizure, and they are hard to control.
  • An electroencephalogram (EEG) shows specific abnormalities.
  • Developmental delays or intellectual disability (not required for diagnosis but often present).

Lab Investigations

There are several useful ways to investigate LGS:

An electroencephalogram, or EEG, is a type of medical test. It measures the electrical activity of the brain. Those with LGS will have an abnormal EEG result. Several typical electrical patterns are seen in most children with LGS. The top two are known as:
  • Generalized paroxysmal fast activity
  • Generalized slow-spike and wave discharge
MRI, or magnetic resonance imaging, can find structural causes of LGS. This may guide treatment decisions. MRI can detect:
  • Cortical malformations
  • Tuberous sclerosis
  • Tumors
  • Acquired brain injury
  • There is no characteristic MRI pattern for LGS. The MRI may be normal.
  • MRI scans are not all the same. An epilepsy-protocol MRI read by an experienced epilepsy neuroradiologist increases the likelihood of detecting an abnormality if one is present.
Sometimes an MRI does not provide a cause. So a genetic test is recommended. These include:
  • Epilepsy gene panel. This is one of the most common genetic tests for epilepsy. It looks for many different genes associated with epilepsy.
  • Chromosomal microarray. This evaluates extra or missing pieces of a chromosome.
  • Whole exome sequencing. This can be ordered by a genetics specialist. It evaluates the entire DNA code. It looks for changes in genes associated with epilepsy. Usually it requires a child and both parents to be tested.
Other tests can look for metabolic, infectious, and autoimmune causes of LGS:
  • Blood tests
  • Urine tests
  • Spinal fluid tests

Repeat Testing

Repeating testing or imaging in older LGS patients can be useful. It can help when an underlying cause has not been determined. It can identify previously missed causes. However, it is not necessary in all cases. Sometimes, genetic testing can be reviewed rather than repeated as our knowledge about genetics grows.

Testing Costs

Insurance generally covers most tests listed above. Genetic testing coverage varies by state and insurance provider.

Diagnostic Codes for LGS

2016: The LGS Foundation helps LGS get designated ICD-10-CM diagnosis codes used under the Health Insurance Portability and Accountability Act (HIPAA). These codes are important and used by the health care system to track health care statistics, disease burden, quality outcomes, mortality statistics, and billing.

    • G40.81 Lennox-Gastaut syndrome
    • G40.811 …… not intractable, with status epilepticus
    • G40.812 …… not intractable, without status epilepticus
    • G40.813 …… intractable, with status epilepticus
    • G40.814 …… intractable, without status epilepticus

Thank you to the Child Neurology Foundation for allowing us to adapt this article for this site.

Authors: Shaun Ajinkya, MD; Elaine Wirrell, MD,  Mayo Clinic – Rochester, Minnesota Reviewed: April 2021

The information here is not intended to provide diagnosis, treatment, or medical advice and should not be considered a substitute for advice from a healthcare professional. The content provided is for informational purposes only. The LGS Foundation is not responsible for actions taken based on the information included on this webpage. Please consult with a physician or other healthcare professional regarding any medical or health related diagnosis or treatment options.

Updated 08/27/22

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