1. Definition
- A rare, age-related epileptic encephalopathy characterized by the subacute onset of Verbal Auditory Agnosia (“word deafness”) and rapid language regression in a child with previously normal development.
- Classified under the spectrum of Epilepsy with Continuous Spike-and-Waves during Slow-Wave Sleep (CSWS).
2. Etiology and Pathophysiology
- Genetic: Mutations in the GRIN2A gene (NMDA receptor subunit) are found in ~20% of cases.
- Autoimmune: Presumed autoimmune mechanism in some cases due to response to steroids/IVIG.
- Functional Lesion: Epileptic discharges originating in the posterior temporal lobe (auditory cortex) disrupt the neural networks required for auditory processing and language retention during the critical period of development.
3. Clinical Features
- Age of Onset: Typically 3–6 years (Range 2–8 years).
- Verbal Auditory Agnosia (Hallmark):
- The child behaves as if deaf, failing to respond to verbal commands despite normal hearing on audiometry.
- Often misdiagnosed initially as acquired deafness or autism.
- Language Regression:
- Loss of receptive language (comprehension) is followed by loss of expressive language.
- Speech becomes “telegraphic,” perseverative, or disappears mutism.
- Non-verbal intelligence and skills usually remain preserved.
- Seizures (~70–75%):
- Occur in the majority but are often infrequent and easily controlled.
- Types: Focal motor seizures (most common), generalized tonic-clonic, atypical absence, or myoclonic seizures.
- Note: ~25–30% of patients may never have clinical seizures, presenting only with aphasia and EEG abnormalities.
- Behavioral: Hyperactivity, attention deficits, and impulsivity are common (frustration due to inability to communicate).
4. Investigations
- Electroencephalogram (EEG) - Gold Standard:
- Awake: High-amplitude focal spikes/sharp waves, typically bitemporal or posterior temporal.
- Sleep (Critical): Marked activation of discharges during non-REM sleep. May progress to CSWS/ESES (Electrical Status Epilepticus during Sleep), where spike-wave index >85% of slow-wave sleep.
- Audiometry: Mandatory to rule out sensorineural hearing loss (results are normal in LKS).
- MRI Brain: Usually normal; performed to exclude structural lesions (tumors, inflammation).
- Genetic Testing: Panel for GRIN2A variants.
5. Management
The primary goal is to preserve language function, not just seizure control.
A. Pharmacotherapy
- Corticosteroids (Mainstay for Aphasia):
- High-dose Prednisolone (2 mg/kg/day) or ACTH. Often required for months to treat the encephalopathy/aphasia.
- “Pulse” IV Methylprednisolone is used in severe cases.
- Antiepileptic Drugs (AEDs):
- First-line: Valproate (VPA), Levetiracetam (LEV), Ethosuximide (ESM), Clobazam (CLB).
- Nocturnal Benzodiazepines: High-dose Diazepam allowed orally/rectally at night to suppress sleep activation.
- Contraindicated (Warning): Carbamazepine, Oxcarbazepine, and Phenytoin. These sodium channel blockers can worsen the CSWS pattern and language deficits.
B. Surgical/Other
- Multiple Subpial Transections (MST): Considered if medical therapy fails (refractory cases). Involves severing horizontal intracortical fibers to stop seizure spread while preserving vertical functional columns.
- Ketogenic Diet: Adjunctive therapy for refractory cases.
- Speech Therapy: Essential. Introduction of sign language may be necessary if auditory agnosia is profound.
6. Prognosis
- Seizures: Generally good. Remission usually occurs by adolescence (age 12–15 years).
- Language: Guarded/Variable.
- Many children are left with permanent language deficits.
- Key Prognostic Factor: Age of onset. Earlier onset (<3 years) carries a worse prognosis for language recovery than later onset (>6 years).
- Fluctuating course is common (“waxing and waning”).