Lennox-Gastaut Syndrome
Lennox-Gastaut syndrome (LGS) is one of the most severe and treatment-resistant epileptic encephalopathies of childhood, accounting for approximately 1–4% of childhood epilepsies but a disproportionate share of the burden of drug-resistant epilepsy. The ILAE 2022 classification defines LGS as a developmental and epileptic encephalopathy characterized by the triad of multiple drug-resistant seizure types (one of which must be tonic seizures), slow (<2.5 Hz) generalized spike-and-wave discharges on the interictal EEG, and cognitive impairment that is either present at onset or develops over time. LGS typically develops between 18 months and 8 years of age and frequently evolves from infantile epileptic spasms syndrome (West syndrome). Despite advances in pharmacotherapy—including cannabidiol, fenfluramine, and rufinamide—LGS remains a challenging condition with poor long-term seizure control and significant neurodevelopmental morbidity.
Bottom Line
- Diagnostic triad: (1) Multiple drug-resistant seizure types with mandatory tonic seizures; (2) slow (<2.5 Hz) generalized spike-and-wave discharges on interictal EEG; (3) cognitive impairment (present at onset or developing over time)
- Seizure types: Tonic seizures (mandatory, often nocturnal), atonic seizures (drop attacks), atypical absence seizures, myoclonic seizures, generalized tonic-clonic seizures, and focal seizures; nonconvulsive status epilepticus is common
- EEG: Slow (<2.5 Hz) generalized spike-and-wave discharges during wakefulness; generalized paroxysmal fast activity (GPFA) during NREM sleep (highly characteristic); background slowing
- Etiology: Diverse; 20–40% evolve from infantile spasms; structural, genetic, and metabolic causes are common; unknown etiology in a minority
- Treatment: Valproate is the traditional first-line; add-on options include clobazam, rufinamide, lamotrigine, cannabidiol, and fenfluramine; the ketogenic diet and vagus nerve stimulation are important nonpharmacologic options; corpus callosotomy for disabling drop attacks
- Prognosis: Drug-resistant in the vast majority; intellectual disability is progressive; mortality is approximately 5% per decade; SUDEP risk is elevated
Epidemiology and Etiology
Demographics
LGS has an estimated incidence of 0.2–0.5 per 100,000 person-years, with onset typically between 18 months and 8 years (peak 3–5 years). It accounts for approximately 1–4% of childhood epilepsies but up to 10% of children with drug-resistant epilepsy. Males are slightly more commonly affected than females. Many adults continue to have LGS; the prevalence of active LGS in adults is estimated at 15,000–30,000 in the United States.
Etiologic Classification
| Etiologic Category | Proportion | Common Causes |
|---|---|---|
| Structural | ~30–40% | Hypoxic-ischemic encephalopathy; malformations of cortical development; tuberous sclerosis; perinatal stroke; CNS infections (meningitis, encephalitis) |
| Evolution from IESS | ~20–40% | Prior infantile spasms (West syndrome) with persistence or transformation of seizures and EEG patterns; the underlying etiologies overlap |
| Genetic | ~10–20% | Many genetic causes; no single gene is predominant; SCN1A, STXBP1, DNM1, CHD2, SYNGAP1, and others have been associated; chromosomal anomalies (Trisomy 21) may also evolve to LGS |
| Unknown | ~20–30% | No identifiable cause despite comprehensive evaluation; this group has relatively better cognitive outcomes compared with identified structural etiologies |
Clinical Features
Seizure Types
LGS is characterized by multiple coexisting seizure types. The presence of tonic seizures is a mandatory diagnostic criterion:
| Seizure Type | Frequency in LGS | Clinical Features | Timing |
|---|---|---|---|
| Tonic seizures | ~90–100% (mandatory) | Brief (5–30 seconds), bilateral tonic stiffening of the trunk and extremities; often subtle (axial tonic posturing); may cause falls | Predominantly during NREM sleep; may occur during wakefulness |
| Atypical absence seizures | ~60–70% | Gradual onset/offset of impaired awareness; changes in tone (head drop, slight trunk flexion); less distinct from baseline than typical absences | Wakefulness; difficult to identify clinically |
| Atonic seizures (drop attacks) | ~40–50% | Sudden loss of muscle tone causing head drops, falls, or collapse; brief (<2 seconds); high injury risk | Wakefulness; unpredictable |
| Myoclonic seizures | ~20–30% | Brief, shock-like jerks; may be generalized or focal | Variable |
| Generalized tonic-clonic seizures | ~15–30% | Bilateral tonic-clonic convulsions | Variable; may be associated with medication changes or illness |
| Focal seizures | ~15–20% | Focal motor or dyscognitive seizures; suggest focal structural lesion | Variable |
| Nonconvulsive status epilepticus | ~50–75% (episodic) | Prolonged periods of obtundation with continuous atypical absence or tonic seizure activity; may last hours to days; often underrecognized | Wakefulness; fluctuating |
Injury Risk and Safety Measures
- Drop attacks: Atonic and tonic seizures cause sudden falls with high risk of facial and dental injuries, lacerations, and head trauma; protective helmets should be prescribed for patients with frequent drop attacks
- Nonconvulsive status epilepticus (NCSE): Occurs in up to 50–75% of patients at some point; presents as prolonged obtundation, increased drooling, subtle myoclonus, or cognitive worsening; may be misinterpreted as behavioral change or medication side effect; EEG confirmation is needed
- SUDEP risk: Patients with LGS have an elevated risk of sudden unexpected death in epilepsy, particularly those with frequent generalized tonic-clonic seizures and nocturnal tonic seizures
- Status epilepticus: Both convulsive and nonconvulsive status epilepticus are relatively common; families should have seizure action plans with rescue medications (rectal diazepam, intranasal midazolam)
Cognitive and Behavioral Features
Cognitive impairment is a defining feature of LGS and is often progressive:
- Intellectual disability is present or develops in >90% of patients, ranging from mild to profound
- Cognitive decline may be partly attributable to the ongoing epileptic encephalopathy (frequent seizures and interictal epileptiform activity disrupting brain networks) and partly to the underlying etiology
- Behavioral problems are common: aggression, hyperactivity, autistic features, and mood disturbances
- Patients with unknown etiology and later onset tend to have better cognitive outcomes than those with structural etiologies or evolution from IESS
EEG Features
Interictal EEG
- Slow spike-and-wave: Generalized discharges at <2.5 Hz (typically 1.5–2.5 Hz), often maximal frontally; morphology is irregular with a "slow" and "heavy" appearance; distinct from the regular 3 Hz spike-and-wave of childhood absence epilepsy
- Background: Diffuse slowing; abnormal and disorganized background activity; lack of the normal posterior dominant rhythm in many patients
Sleep EEG
- Generalized paroxysmal fast activity (GPFA): Runs of generalized, rhythmic, fast activity at 10–25 Hz during NREM sleep, typically lasting 1–10 seconds; this finding is highly characteristic of LGS and may be present even when the waking EEG is nondiagnostic
- GPFA may or may not be associated with a clinical tonic seizure
- Sleep EEG is therefore essential for diagnosis; an EEG limited to wakefulness may miss the hallmark features of LGS
Diagnostic Approach
- The diagnosis of LGS requires all three components of the triad: multiple seizure types including tonic seizures, slow spike-and-wave on EEG, and cognitive impairment
- A prolonged or overnight EEG capturing NREM sleep is recommended to identify GPFA and nocturnal tonic seizures
- Brain MRI with epilepsy protocol is mandatory to evaluate for structural etiologies
- Genetic testing (exome sequencing) should be considered in all patients, particularly when no structural cause is identified
- Reassess the diagnosis if tonic seizures are absent—consider other epileptic encephalopathies such as epilepsy with myoclonic-atonic seizures (Doose syndrome) or DEE-SWAS
Differential Diagnosis
Several other childhood epileptic encephalopathies may mimic LGS, and accurate differentiation is important for treatment selection and prognostic counseling:
| Condition | Key Distinguishing Features | EEG |
|---|---|---|
| Epilepsy with myoclonic-atonic seizures (Doose syndrome) | Onset age 2–6 years in previously normally developing children; myoclonic-atonic seizures are the hallmark (not tonic seizures); initial explosive onset may be alarming; two-thirds achieve remission | Generalized 2–6 Hz spike-and-wave or polyspike-and-wave; NO generalized paroxysmal fast activity; normal background initially |
| Dravet syndrome | Onset <1 year; prolonged fever-sensitive seizures; SCN1A pathogenic variant in >80%; tonic seizures are atypical for Dravet | Focal, multifocal, and generalized discharges; NOT slow spike-and-wave |
| DEE-SWAS (CSWS) | Cognitive regression with ESES pattern during sleep; not dominated by tonic seizures; SWI ≥50% | Near-continuous spike-wave during NREM sleep; different from GPFA pattern of LGS |
| Infantile epileptic spasms (evolving) | Transition phase from IESS to LGS; spasms may coexist with early tonic seizures; hypsarrhythmia evolves to slow spike-and-wave | Mixed features; hypsarrhythmia may transition to LGS-type EEG pattern |
| Progressive myoclonus epilepsies | Progressive ataxia and myoclonus with cognitive decline; onset variable; specific metabolic or genetic causes (Lafora, Unverricht-Lundborg, NCL) | Variable; often photosensitive; background deteriorates progressively |
Key Diagnostic Points
- The presence of tonic seizures is a mandatory criterion for LGS—if no tonic seizures are documented, reconsider the diagnosis
- Generalized paroxysmal fast activity (GPFA) in sleep is highly characteristic of LGS and may be the most reliable EEG feature; an overnight or prolonged EEG is essential
- Doose syndrome (epilepsy with myoclonic-atonic seizures) is often confused with LGS but has a markedly better prognosis (two-thirds achieve remission); differentiating the two has significant treatment and counseling implications
- Drug-resistant epilepsy with multiple seizure types in a child does NOT automatically equal LGS—formal diagnostic criteria must be met
Treatment
Pharmacotherapy
No single medication achieves seizure freedom in the majority of patients with LGS. Treatment is aimed at reducing seizure frequency and severity, particularly targeting disabling seizure types such as drop attacks and tonic-clonic seizures:
| Medication | Mechanism | Evidence/Indication | Key Notes |
|---|---|---|---|
| Valproate | Multiple (GABA, Na+, Ca2+) | Traditional first-line; broad-spectrum antiseizure effect | Teratogenic; weight gain; hepatotoxicity risk in young children; monitor levels, LFTs, CBC |
| Clobazam | GABAA receptor agonist (1,5-benzodiazepine) | FDA-approved for LGS (age ≥2); reduces drop attacks by ~50% in RCTs | Better tolerated than other benzodiazepines; sedation, drooling; tolerance may develop; CYP2C19 poor metabolizers at higher risk for side effects |
| Rufinamide | Sodium channel modulation (distinct from CBZ/PHT) | FDA-approved for LGS (age ≥1); significant reduction in tonic-atonic seizures | Generally well tolerated; dizziness, nausea, vomiting; shortens QT interval (avoid in short QT syndrome) |
| Cannabidiol (Epidiolex) | Multiple (GPR55, TRPV1, adenosine reuptake) | FDA-approved for LGS (age ≥1); 42–44% reduction in drop seizures vs. 17–22% placebo (GWPCARE3/4 trials) | Hepatotoxicity (monitor LFTs, especially with concomitant valproate); drug interactions (increases clobazam active metabolite); somnolence, diarrhea |
| Fenfluramine (Fintepla) | Serotonin release/reuptake inhibition; sigma-1 receptor agonist | FDA-approved for LGS (age ≥2); 26% median reduction in GTC seizures vs. 7% placebo | Requires echocardiographic monitoring (risk of valvular heart disease, pulmonary arterial hypertension; available through REMS program); decreased appetite; somnolence |
| Lamotrigine | Na+ channel blocker; glutamate modulation | Add-on therapy; effective against drop attacks, tonic, and GTC seizures | Slow titration required (SJS risk, especially with concomitant valproate); may worsen myoclonic seizures in some patients |
| Topiramate | Multiple (Na+, GABA, AMPA/kainate, CA inhibition) | Add-on therapy; 33% reduction in drop attacks in RCT | Cognitive side effects; metabolic acidosis; nephrolithiasis; weight loss |
| Felbamate | Multiple (NMDA, GABA, Na+) | Effective for LGS; reserve for refractory cases | Aplastic anemia and hepatic failure (both rare but potentially fatal); requires regular CBC and LFT monitoring; informed consent and REMS program |
Nonpharmacologic Therapies
- Ketogenic diet: Effective in approximately 40–50% of patients with LGS (>50% seizure reduction); should be considered early, particularly in drug-resistant cases; requires a dedicated ketogenic diet team
- Vagus nerve stimulation (VNS): Adjunctive therapy; approximately 50% of patients achieve ≥50% seizure reduction over time; gradual improvement over years; well tolerated; voice hoarseness is the most common side effect
- Corpus callosotomy: Palliative surgical option specifically for disabling drop attacks (atonic and tonic seizures causing falls); anterior two-thirds callosotomy reduces drop attacks in approximately 50–80% of patients; does not achieve seizure freedom but significantly reduces injury risk
- Responsive neurostimulation (RNS) and deep brain stimulation (DBS): Emerging evidence for their use in LGS, particularly centromedian thalamic DBS, which targets the thalamocortical networks involved in generalized seizures
Medications to Avoid in LGS
- Carbamazepine and oxcarbazepine: May worsen atypical absence seizures, tonic seizures, and drop attacks; can precipitate nonconvulsive status epilepticus
- Phenytoin: May exacerbate atypical absences and tonic seizures
- Vigabatrin: Can worsen generalized epilepsy syndromes, including LGS
- Gabapentin and pregabalin: May exacerbate generalized seizure types
Landmark Clinical Trials in LGS
| Trial | Drug | Design | Key Results |
|---|---|---|---|
| CONTAIN (2011) | Clobazam | Phase 3, randomized, double-blind, placebo-controlled; N=238 | Dose-dependent reduction in drop seizures; high-dose clobazam: 68% responder rate vs. 32% placebo; FDA approval for LGS |
| Rufinamide RCT (2008) | Rufinamide | Phase 3, randomized, double-blind, placebo-controlled; N=139 | 32.7% median reduction in tonic-atonic seizure frequency vs. 11.7% increase with placebo; FDA approval for LGS |
| GWPCARE3 (2018) | Cannabidiol (Epidiolex) | Phase 3, randomized, double-blind, placebo-controlled; N=225 | CBD 20 mg/kg/day: 44% median reduction in drop seizures vs. 22% placebo; significant improvement in caregiver global impression of change |
| GWPCARE4 (2018) | Cannabidiol (Epidiolex) | Phase 3, randomized, double-blind, placebo-controlled; N=171 | CBD 20 mg/kg/day: 42% reduction in drop seizures vs. 17% placebo; confirmed dose-response relationship; both studies led to FDA approval |
| Fenfluramine LGS (2022) | Fenfluramine (Fintepla) | Phase 3, randomized, double-blind, placebo-controlled; N=263 | 26.5% median reduction in GTC seizures (0.7 mg/kg/day) vs. 6.6% placebo; FDA approval for LGS (second indication after Dravet) |
Prognosis and Transition to Adulthood
LGS is a lifelong condition with guarded prognosis:
- Seizure control: Drug-resistant epilepsy persists in >90% of patients; complete seizure freedom is rare
- Cognitive outcomes: Progressive intellectual disability in the majority; only 5–10% maintain normal or near-normal cognition
- Seizure evolution: Seizure types may change over time; tonic seizures often persist into adulthood; the slow spike-and-wave pattern may become less prominent; some patients experience a shift from generalized to more focal seizure patterns
- EEG evolution: The classic slow spike-and-wave pattern may become less prominent in adulthood, though GPFA in sleep often persists; the EEG may lose its "classic" LGS appearance, potentially leading to diagnostic uncertainty in adult epilepsy clinics unfamiliar with the diagnosis
- Mortality: Estimated 5% per decade; causes include SUDEP, status epilepticus, aspiration pneumonia, and complications of the underlying condition; overall life expectancy is reduced compared with the general population
Transition to Adult Care
The transition from pediatric to adult epilepsy services is a critical period for patients with LGS:
- Planning: Transition planning should begin at age 14–16 and involve the pediatric and adult neurology teams, primary care, social work, and the family
- Documentation: A comprehensive medical summary including seizure history, EEG evolution, medication trials and responses, comorbidities, and functional status should accompany the transition
- Guardianship and legal planning: Many adults with LGS lack capacity for independent medical decision-making; legal guardianship or healthcare proxy should be established before age 18
- Residential and vocational services: The majority of adults with LGS require supported living arrangements; vocational programs tailored to the individual's cognitive abilities should be explored
- Medication management: Adult providers should be familiar with the medication history, including drugs that were ineffective or harmful, to avoid unnecessary re-trials; polypharmacy is common and warrants regular review
- Quality of life: Caregiver burden is substantial; respite care, family support services, and mental health support for caregivers should be integrated into the care plan
Emerging Therapies for LGS
- Centromedian thalamic deep brain stimulation (DBS): Targets the centromedian nucleus of the thalamus, a key node in the thalamocortical networks generating generalized seizures; phase 3 trial (ESTEL) showed significant reduction in generalized seizures; FDA approval anticipated
- Responsive neurostimulation (RNS): Originally designed for focal epilepsy, emerging data suggest benefit in LGS when targeted to key network nodes
- Ganaxolone: A neuroactive steroid GABAA receptor positive allosteric modulator; has shown benefit in some epileptic encephalopathies and is under investigation for LGS
- Gene therapy: For specific genetic etiologies of LGS, targeted gene therapy approaches are in early development
- Ongoing clinical trials: Multiple novel compounds are in various stages of clinical development for LGS, reflecting the significant unmet need in this population
References
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