What are the clinical and EEG characteristics of early Lennox-Gastaut syndrome in children?

Identifying Early Lennox-Gastaut Syndrome in Children

Early Lennox-Gastaut syndrome (LGS) is identified by the presence of multiple seizure types (which must include tonic seizures), characteristic EEG abnormalities showing diffuse slow spike-and-wave complexes at 1-2.5 Hz, and cognitive/behavioral impairment, with typical onset between 1-8 years of age. 1, 2

Clinical Characteristics at Presentation

Age of Onset and Evolution

• Peak onset occurs between 1-4 years of age, accounting for 61% of cases 3
• Onset can range from 8 months to 12 years, though onset after 8 years is unusual 3
• Approximately 18% of cases evolve from West syndrome (infantile spasms), and this transformation should be actively monitored in infants with West syndrome 3

Seizure Types (Multiple Types Required)

The hallmark is the presence of multiple seizure types, with tonic seizures being essential for diagnosis, though they may not be present at initial onset: 1

• Tonic seizures: Characteristic but often absent at disease onset; develop over time and are considered pathognomonic when present 1, 3
• Atypical absence seizures: Present in most cases but difficult to identify clinically without EEG confirmation—parents cannot reliably count these seizures based on observation alone 4
• Atonic seizures (drop attacks/head drops): Result in sudden falls with high risk of injury 3, 5
• Tonic-clonic seizures: Frequently present and reliably identified by parents 4

Critical pitfall: Do not rely on parental observation alone to diagnose atypical absence seizures—video-EEG monitoring is essential, as suspected atypical absences are confirmed as epileptic seizures in only 27% of cases 4

Cognitive and Behavioral Features

• Mental deficit ranges from slight to profound deterioration 3
• Mental and behavioral disturbances exist in every case as a rule 3
• Cognitive impairment is a core feature and should be assessed at presentation 1, 2

EEG Characteristics

Essential EEG Features for Diagnosis

The EEG must demonstrate the following abnormalities, though they are not pathognomonic: 1

• Diffuse slow spike-and-wave complexes at 1-2.5 Hz (classically described as <3 Hz): This is the cardinal EEG feature, predominant in frontal and temporal regions 3, 5
• Abnormal background activity: Present in all cases 3
• Polyspike-wave discharges: Observed in approximately 39% of cases (24 of 62 patients) 3
• Bursts of fast rhythms (10-14 Hz) during sleep: Found in approximately 47% of cases (29 of 62 patients), particularly during tonic seizures 3

EEG Monitoring Strategy

• Obtain baseline EEG at initial evaluation when LGS is suspected 1
• Video-EEG monitoring is mandatory for accurate seizure classification, particularly for atypical absence seizures, as clinical observation is unreliable 4
• Sleep EEG recordings are important to capture fast rhythms associated with tonic seizures 3

Diagnostic Algorithm

Step 1: Clinical Suspicion

Suspect early LGS in children aged 1-8 years presenting with:

• Multiple seizure types (at least 2 types) 3
• Developmental delay or cognitive regression 1, 3
• History of West syndrome or infantile spasms 3

Step 2: Seizure Documentation

• Obtain detailed seizure history from caregivers 1
• Do not accept parental counts of atypical absence seizures without EEG confirmation 4
• Parents can reliably identify tonic, atonic, and tonic-clonic seizures 4

Step 3: EEG Confirmation

• Perform routine EEG with sleep recording 3
• Look for slow spike-wave complexes (1-2.5 Hz) with abnormal background 3, 5
• If atypical absences are suspected, proceed to video-EEG monitoring for definitive classification 4

Step 4: Etiologic Evaluation

• Classify as symptomatic (secondary to brain disorder) or cryptogenic (no known cause) 1
• Perinatal events are the predominant factors in symptomatic cases 3
• Brain MRI should be obtained to identify structural abnormalities 6

Key Diagnostic Pitfalls to Avoid

1. Waiting for tonic seizures: Tonic seizures are characteristic but not present at onset in many cases—do not delay diagnosis if other criteria are met 1

2. Relying on clinical observation for atypical absences: These require video-EEG confirmation, as 73% of suspected events are non-epileptic 4

3. Expecting pathognomonic EEG features: The slow spike-wave pattern is characteristic but not unique to LGS 1

4. Missing the evolution from West syndrome: Actively monitor infants with infantile spasms for transformation to LGS 3

5. Overlooking late-onset cases: While unusual, onset can occur after 8 years and even into adulthood 3

Prognostic Considerations

Early identification is critical because:

• LGS is profoundly impairing with poor responsiveness to antiepileptic medications 6
• Early intervention may improve mental and behavioral development 3
• Seizures are drug-resistant in most cases, requiring consideration of non-pharmacological treatments 5
• The long-term outlook is poor for most patients without aggressive management 1