Landau-Kleffner syndrome and electrical status epilepticus in sleep (ESES / CSWS)
A rare childhood epileptic encephalopathy in which a previously well child loses language (or other cognitive functions) over weeks to months, with a striking sleep-EEG of near-continuous spike-and-wave.
Landau-Kleffner syndrome (LKS) and the broader category of epileptic encephalopathy with spike-wave activation in sleep (EE-SWAS, previously called CSWS or ESES) are uncommon but important paediatric conditions in which a child who had been developing normally develops a marked, progressive loss of language (LKS) or wider cognitive and behavioural function (EE-SWAS), coinciding with an EEG that becomes dominated by near-continuous spike-and-wave during slow-wave sleep. The seizures themselves are often mild or even absent — it is the relentless interictal discharges in sleep that drive the regression. Recognition matters because the cognitive losses, while sometimes reversible with timely treatment, become harder to recover the longer the EEG remains active. Treatment is increasingly evidence-based but still difficult: high-dose benzodiazepines, corticosteroids or ACTH, sulthiame, valproate, levetiracetam, IVIG and the ketogenic diet are all used in sequence, and surgical disconnection (multiple subpial transection or hemispherotomy) is reserved for refractory lesional cases.
At a glance
- Onset
- Typically 3–8 years, peak 5–7
- Hallmark (LKS)
- Acquired auditory verbal agnosia: a previously well child can no longer understand spoken language
- Hallmark (EE-SWAS / ESES)
- Global cognitive, behavioural and motor regression beyond language
- EEG
- Near-continuous (>50–85%) spike-and-wave in non-REM sleep; awake EEG often relatively normal
- Course
- Seizures and EEG usually remit by mid-teens; cognitive outcome depends on how early the EEG is brought under control
What it is
Landau and Kleffner first described, in 1957, six children who developed a striking and otherwise unexplained loss of the ability to understand spoken language — alongside an EEG that was full of bilateral temporal spikes that intensified in sleep. Decades later we recognise LKS as the most language-specific end of a wider spectrum (now grouped under the umbrella term 'epileptic encephalopathy with spike-wave activation in sleep' (EE-SWAS) in the 2022 ILAE syndromes paper).
The common thread is that intense interictal epileptiform activity during sleep — at a level that does not occur naturally in healthy children — drives a measurable, progressive loss of cognitive function. When the activity is concentrated over the perisylvian language areas, the loss is mostly in language understanding (LKS). When it is more diffuse, the loss is global (EE-SWAS / CSWS).
How it presents
Families and teachers usually notice one of three patterns:
- A child between 3 and 8 who was developing normally begins to seem unaware of speech — they don't respond to their name, the TV no longer holds their attention by sound alone, they 'don't listen', and may even be assessed for hearing loss
- A child whose school performance, attention and behaviour deteriorate sharply over weeks or months, with new tantrums, regression of social skills and sometimes a loss of motor skills (EE-SWAS / CSWS)
- Seizures — focal motor (often nocturnal hemifacial), atypical absences, or atonic seizures — sometimes prompt the EEG that reveals the diagnosis. Seizures can also be entirely absent in classic LKS
An audiogram is normal. The child can hear — they have lost the ability to PROCESS spoken language at the cortical level. This is acquired auditory verbal agnosia.
Diagnosis
The diagnosis combines the regression history, formal language and cognitive assessment, and — most importantly — a whole-night sleep EEG showing spike-and-wave activation in non-REM sleep exceeding 50% of the recording (some series use 85%). A short, daytime EEG may be normal or only mildly abnormal; an overnight or extended sleep recording is essential.
Brain MRI is usually normal but is needed to exclude a structural cause (cortical dysplasia, polymicrogyria — particularly perisylvian — small infarcts, tumours).
Genetic testing identifies a likely cause in 10–20% of cases, most often GRIN2A (associated with the LKS / epilepsy-aphasia spectrum).
Treatment
Treatment is challenging because the goal is not just stopping clinical seizures but suppressing the sleep-EEG long enough for the cognitive functions to recover. There is broad expert consensus that aggressive, EEG-guided treatment matters, but the optimal sequence and duration are still being refined.
- High-dose corticosteroids or ACTH — the most consistently effective first-line treatment; many regimens use prednisolone 1–2 mg/kg/day for 4–8 weeks, then taper over months, with EEG monitoring
- Benzodiazepines, particularly high-dose oral diazepam or clobazam — alternative or add-on, often as a pulse over 3–4 weeks
- Sulthiame — widely used in continental Europe with good evidence, especially in the GRIN2A spectrum
- Valproate and levetiracetam — used as baseline antiseizure cover
- Avoid carbamazepine, oxcarbazepine and phenytoin where possible — they can worsen the EEG and the regression
- IVIG — small-series evidence, sometimes used when steroids fail or contraindicated
- Ketogenic diet — increasingly tried when medication fails
- Surgery (multiple subpial transection, hemispherotomy for unilateral lesional cases) — reserved for refractory patients with structural cause
Prognosis
The EEG and seizures usually settle by mid- to late adolescence in essentially all children. Cognitive recovery is more variable: with early aggressive treatment that brings the sleep EEG under control within the first year, many children recover most of their lost language and cognitive function. With longer delays, residual deficits — particularly in receptive language, working memory and attention — often persist into adult life. Hence the emphasis on early recognition and proactive treatment.
How an educational review can help
Families often arrive at clinic worried about a child whose school report has fallen off a cliff over a single term, and who has had a 'normal' awake EEG. An educational review can explain the value of an overnight EEG, place the picture in the EE-SWAS / LKS spectrum, and pull together the current evidence for the steroid, sulthiame and benzodiazepine regimens used at different centres — all to help you prepare the right questions for your treating epilepsy team.
It is an educational second opinion — not a diagnosis, treatment or prescription — and it does not replace the care of your child's own clinicians.
Selected sources
- Specchio N et al. ILAE classification and definition of epilepsy syndromes with onset in childhood. Epilepsia. 2022; 63: 1398–1442.
- Tassinari CA, Rubboli G. Encephalopathy related to electrical status epilepticus during slow sleep (ESES / CSWS): a long-running puzzle. Epilepsia 2019.
- Lemke JR et al. Mutations in GRIN2A cause idiopathic focal epilepsy with rolandic spikes and the LKS spectrum. Nat Genet 2013 (and follow-up cohort studies).
- Sánchez Fernández I et al. The natural history and treatment of encephalopathy with status epilepticus in sleep. Epilepsia 2018 / 2024 update.
Last reviewed: 2026-05-27
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