Generalized Epilepsy EEG Patterns

Generalized epilepsies — childhood absence, juvenile absence, juvenile myoclonic epilepsy (JME), and the epileptic encephalopathies like Lennox-Gastaut — produce distinctive EEG patterns that allow syndromic diagnosis from the EEG alone. The bilateral synchronous, generalized morphology of spike-and-wave discharges, the characteristic frequencies of different syndromes, and the activation by sleep, awakening, photic stimulation, and hyperventilation all combine to make generalized epilepsy EEG some of the most clinically informative tracings in epilepsy. This page covers the canonical patterns by syndrome, the criteria for syndromic diagnosis, and the activation procedures that confirm each.

Childhood Absence Epilepsy (CAE)

Clinical

• Age of onset: 4–10 years (peak 6–7).
• Multiple daily absences: brief (3–20 seconds) staring, behavioral arrest, often with subtle automatisms or eyelid flicker.
• Normal cognition and development.
• Excellent prognosis with treatment.

EEG

• Background: normal posterior dominant rhythm for age.
• Ictal: bilateral synchronous, anterior-dominant 3-Hz spike-and-wave at onset, slowing to 2.5 Hz at end of burst.
• Burst duration: typically 5–20 seconds.
• Sharply contoured spike-and-wave morphology.
• Hyperventilation provokes seizures in ~90% of cases — diagnostic.
• Photic stimulation can also provoke.

Atypical Absence (Distinguish from CAE)

• Slower (1.5–2.5 Hz) generalized spike-and-wave.
• Often in setting of underlying brain abnormality.
• Longer duration, less abrupt onset/offset.
• Associated with Lennox-Gastaut syndrome rather than benign genetic generalized epilepsy.

Juvenile Absence Epilepsy (JAE)

• Age of onset: 10–17 years.
• Less frequent absences than CAE; may be associated with generalized tonic-clonic seizures.
• EEG: bilateral synchronous spike-and-wave at 3.5–4 Hz, slightly faster than CAE.
• Less reliable HV activation than CAE.

Juvenile Myoclonic Epilepsy (JME)

Clinical

• Age of onset: 12–18 years.
• Triad: myoclonic jerks (especially on awakening), generalized tonic-clonic seizures, absence seizures (less common).
• Photosensitive in 30–40%.
• Sleep deprivation, alcohol withdrawal, photic stimulation are triggers.
• Lifelong condition; pharmacoresistant if untreated, but most respond to valproate.

EEG

• Background: usually normal.
• Interictal: bilateral synchronous polyspike-and-wave at 4–6 Hz, often anterior or bilateral.
• Ictal myoclonic jerks: brief (1–2 sec) generalized polyspike-and-wave with high amplitude.
• Activated by sleep deprivation, awakening, photic stimulation.
• Often photoconvulsive response (sustained polyspike-wave outlasting photic train).

Generalized Epilepsy with Generalized Tonic-Clonic Seizures Alone

• Adolescent onset.
• Generalized tonic-clonic seizures without absence or prominent myoclonus.
• EEG: occasional generalized spike-and-wave bursts; otherwise normal.
• Often genetic.

Lennox-Gastaut Syndrome (LGS)

Clinical

• Age of onset: 1–8 years (peak 3–5).
• Triad: multiple seizure types (tonic, atonic, atypical absence, myoclonic, focal), cognitive impairment, characteristic EEG.
• Often follows West syndrome (infantile spasms).
• Pharmacoresistant; lifelong disability common.

EEG

• Background: slow for age, often diffuse 1.5–2.5 Hz polymorphic delta.
• Interictal: bilateral synchronous slow spike-and-wave at 1.5–2.5 Hz.
• Generalized paroxysmal fast activity (GPFA): bursts of 10–25 Hz low-amplitude activity, often during sleep, associated with tonic seizures.
• Multifocal sharp waves.
• Activation by sleep dramatic.

West Syndrome / Infantile Spasms

Clinical

• Age of onset: 4–10 months.
• Triad: infantile spasms (brief flexion/extension of arms and legs in clusters), psychomotor regression, hypsarrhythmia on EEG.
• Etiologies: tuberous sclerosis, structural lesions, genetic syndromes, metabolic disorders, often unknown.
• Treatment: ACTH, vigabatrin (especially in tuberous sclerosis), corticosteroids.
• Prognosis often poor; often progresses to LGS.

EEG: Hypsarrhythmia

• Disorganized, chaotic, high-amplitude (often >300 μV) background.
• Multifocal asynchronous spikes and sharp waves across all regions.
• “Modified hypsarrhythmia”: some preservation of background organization or focal predominance.
• Often more prominent in slow-wave sleep than wake.
• Ictal spasm: brief diffuse high-amplitude slow wave followed by brief attenuation (“electrodecremental response”).

Generalized Epilepsy with Febrile Seizures Plus (GEFS+)

• Genetic syndrome (SCN1A and others).
• Febrile seizures continuing beyond age 6.
• Various afebrile seizure types in same family.
• EEG: variable; may show generalized spike-and-wave or focal IEDs.

Doose Syndrome (Myoclonic-Atonic Epilepsy)

• Age of onset: 2–5 years.
• Multiple seizure types: myoclonic-atonic (“drop” attacks), absence, tonic-clonic.
• EEG: generalized spike-and-wave or polyspike-wave at 2–4 Hz.
• Often responds well to ketogenic diet or valproate.

Dravet Syndrome (Severe Myoclonic Epilepsy of Infancy)

• SCN1A mutation in 80%.
• Onset in first year with febrile status epilepticus.
• Multiple seizure types: febrile, myoclonic, absence, focal.
• EEG: variable; may include generalized spike-and-wave, focal IEDs, photoparoxysmal response.
• Treatment: AVOID sodium channel blockers (carbamazepine, oxcarbazepine, lamotrigine, phenytoin) — worsen seizures.
• Use valproate, clobazam, stiripentol, cannabidiol, fenfluramine.

Recognition of Each Pattern

Special Features

Photoparoxysmal Response

• Common in generalized epilepsies.
• Different patterns:
  • Photoconvulsive (sustained 3 Hz SW outlasting stimulus): JME, photosensitive epilepsy.
  • Photoparoxysmal (brief SW within photic train): JME, juvenile absence.
• Family history positive for photosensitive epilepsy common.

Eyelid Myoclonia with Absences (Jeavons Syndrome)

• Eye closure-induced eyelid myoclonia.
• Brief absences.
• Photosensitive.
• EEG: generalized polyspike-wave often triggered by eye closure.

Generalized Tonic Seizures

• Sustained muscle contraction without clonic phase.
• Common in LGS.
• EEG: GPFA (10–25 Hz fast activity), often during sleep.

Distinguishing Generalized from Secondarily Generalized

• Truly generalized epilepsies: bilateral synchronous onset from the start.
• Focal seizures with secondary generalization: focal aura → focal motor → bilateral.
• Clinical history of aura, post-ictal lateralization, asymmetric motor activity → focal origin.
• Treatment differs: generalized epilepsies often respond to valproate; focal often respond to lamotrigine, levetiracetam.

Pharmacologic Effects on Generalized Patterns

• Valproate: reduces spike-wave; can produce normalization of EEG.
• Ethosuximide: specific for absence epilepsies.
• Lamotrigine: reduces interictal IEDs; effective in JME (but caution with MAS).
• Carbamazepine, oxcarbazepine: may worsen JME, absence, myoclonus.
• Discontinuation of these triggers IED recurrence.

🔍 Did You Know?

The idiosyncratic worsening of juvenile myoclonic epilepsy (JME) by sodium-channel-blocking antiepileptic medications — carbamazepine, oxcarbazepine, lamotrigine in some patients, phenytoin — is one of the most clinically important paradoxical drug effects in epilepsy. Patients with JME respond well to valproate, levetiracetam, topiramate, and zonisamide, but can have dramatic worsening of myoclonic jerks and absences when started on carbamazepine or oxcarbazepine — sometimes with provoked status myoclonic. This was a major source of medical errors before the syndrome was widely recognized: a patient with “generalized tonic-clonic seizures” started on carbamazepine could have weeks of worsening myoclonus before the diagnosis was reconsidered. The lesson is that syndromic classification of epilepsy directly informs medication choice, and getting the syndrome wrong can make the patient worse. Recognition of JME’s classic EEG pattern (bilateral 4–6 Hz polyspike-wave, photoconvulsive response, sleep deprivation activation) is therefore not just an academic exercise — it directly prevents drug-induced exacerbation. The same caution applies to Dravet syndrome (sodium channel blockers worsen) and atypical absences in Lennox-Gastaut (carbamazepine can worsen). For practicing neurologists, the clinical pearl: before treating “generalized epilepsy” with carbamazepine, look for syndromic clues that the patient might actually have JME or Dravet.

Pitfalls and Pearls

• CAE: 3-Hz spike-wave; HV provokes; normal background; excellent prognosis.
• JAE: 3.5–4 Hz spike-wave; older onset.
• JME: 4–6 Hz polyspike-wave; sleep deprivation + photic + awakening triggers.
• JME drugs to avoid: carbamazepine, oxcarbazepine can worsen.
• LGS: 1.5–2.5 Hz slow SW; GPFA in sleep; tonic + atonic + atypical absence.
• West syndrome: hypsarrhythmia; infantile spasms; ACTH, vigabatrin.
• Dravet: SCN1A; AVOID Na⁺ blockers; valproate + clobazam + stiripentol.
• Doose syndrome: myoclonic-atonic; often responds to ketogenic diet.
• Eyelid myoclonia with absences (Jeavons): eye closure-induced.
• Atypical vs typical absence: atypical is slower (1.5–2.5 Hz), in LGS context.
• Photoconvulsive response: sustained SW outlasting photic; clinically significant.
• HV provokes 3-Hz SW in CAE: ~90% sensitivity.
• Truly generalized: bilateral synchronous from start; focal-to-bilateral has aura and lateralization.
• Valproate first-line for generalized epilepsies: but AVOID in women of childbearing age.
• Modified hypsarrhythmia: some preservation of organization; often focal origin.
• Generalized paroxysmal fast activity (GPFA): tonic seizure marker in LGS.
• Syndromic classification matters for drug choice: get the syndrome wrong, make the patient worse.

References

1. Engel J Jr. Report of the ILAE classification core group. Epilepsia. 2006;47(9):1558-1568.
2. Scheffer IE, Berkovic S, Capovilla G, et al. ILAE classification of the epilepsies: position paper of the ILAE Commission for Classification and Terminology. Epilepsia. 2017;58(4):512-521.
3. Genton P, Gélisse P, Thomas P, Dravet C. Do carbamazepine and phenytoin aggravate juvenile myoclonic epilepsy? Neurology. 2000;55(8):1106-1109.
4. Ebersole JS, Husain AM, Nordli DR Jr, eds. Current Practice of Clinical Electroencephalography. 4th ed. Wolters Kluwer; 2014.
5. Hirsch E, French J, Scheffer IE, et al. ILAE definition of the Idiopathic Generalized Epilepsy Syndromes. Epilepsia. 2022;63(6):1475-1499.