Developmental and/or Epileptic Encephalopathy with Spike-and-Wave Activation in Sleep (D/EE-SWAS)

Developmental and/or epileptic encephalopathy with spike-and-wave activation in sleep (D/EE-SWAS) is a childhood epilepsy syndrome in which epileptiform activity becomes dramatically more abundant during non-REM sleep and is associated with regression or stagnation in cognition, language, behaviour or motor function.

Older literature may use terms such as continuous spike-and-wave during slow-wave sleep (CSWS) or electrical status epilepticus during sleep (ESES). Modern ILAE terminology separates the EEG phenomenon of spike-wave activation in sleep from the clinical syndrome and recognises both developmental and epileptic contributions to impairment.

Why the terminology changed

The older term ESES often focused on a numerical EEG threshold, historically a spike-wave index of 85% or more of slow-wave sleep.

The modern ILAE approach recognises that clinically important cognitive or behavioural regression can occur with lower percentages and that the relationship between sleep EEG burden and impairment is more complex than one cut-off.

What makes this a syndrome rather than an EEG finding?

Abundant spike-wave activity during sleep alone is not enough.

The syndrome requires a compatible childhood clinical course with developmental, cognitive, language, behavioural or motor deterioration linked in time to marked activation of epileptiform activity during sleep.

Typical age

D/EE-SWAS is a childhood-onset syndrome. The regression or plateau generally appears after a period in which development was stable or progressing.

Some children have pre-existing developmental impairment, while others were developing normally before the sleep-activated epileptic encephalopathy emerged.

Seizures

Seizure types vary. Children may have focal seizures, generalised seizures or both.

Importantly, the developmental decline can be more clinically significant than the visible seizure burden.

The sleep EEG is central

During wakefulness, the EEG may show focal or multifocal epileptiform activity, generalised discharges or even relatively little abnormality.

In non-REM sleep, epileptiform activity becomes markedly activated, often as slow 1.5–2 Hz spike-wave complexes that can be diffuse, frontal-predominant, focal or multifocal.

Why an overnight EEG may be necessary

A short routine EEG may not capture sufficient non-REM sleep to reveal the full abnormality.

The ILAE notes that an overnight sleep EEG may be required because slow-wave sleep may not occur during a short outpatient recording.

Sleep architecture can be disrupted

Normal sleep features such as spindles, K complexes and vertex waves may become difficult to identify when epileptiform activity is very abundant.

This disruption may itself contribute to impaired memory consolidation and daytime function.

Regression can affect different domains

Some children mainly lose language skills. Others show deterioration in attention, learning, executive function, behaviour, motor planning or global cognition.

The pattern can depend partly on the location and distribution of the epileptiform network and the underlying cause.

Relationship to Landau–Kleffner syndrome

Landau–Kleffner syndrome has historically been described separately because acquired language regression is dominant.

Modern classification places language-predominant cases within the broader sleep-activated epileptic encephalopathy spectrum while recognising their distinctive clinical presentation.

Relationship to SeLECTS

A small proportion of children with self-limited epilepsy with centrotemporal spikes can evolve into a more severe sleep-activated encephalopathy with cognitive, language or behavioural regression.

This is one reason new regression in a child previously thought to have uncomplicated SeLECTS requires reassessment and sleep EEG.

Causes

D/EE-SWAS can be associated with structural brain abnormalities, genetic conditions or no identified cause.

Genetic causes include a number of genes involved in neurodevelopment and synaptic function. Structural lesions can include perinatal injury, cortical malformation and other focal abnormalities.

MRI

MRI is important because a structural cause can change management and may identify a child who should be considered for epilepsy-surgery assessment.

A normal MRI does not exclude the syndrome.

Genetic testing

Genetic testing is increasingly important, especially when MRI does not provide a clear cause or when developmental abnormalities pre-date the sleep-activated EEG pattern.

Testing strategy may include an epilepsy panel, exome sequencing or genome sequencing depending on the health system.

Why early recognition matters

Persistent sleep-activated epileptiform activity can be associated with lasting neurocognitive impairment.

The treatment goal is therefore not simply seizure reduction; clinicians also aim to suppress the pathological sleep EEG pattern and protect development.

Treatment evidence is limited

Despite the seriousness of the syndrome, high-quality randomised evidence is sparse. A 2024 systematic review highlighted major gaps in treatment evidence and the absence of one universally approved therapy.

This uncertainty should be stated clearly rather than presenting one treatment as proven for all children.

Medicines used in practice

Benzodiazepines, corticosteroids and various broad-spectrum antiseizure medicines are used in different centres.

Response varies, and treatment selection often depends on the EEG pattern, underlying cause, developmental trajectory and previous therapies.

Steroid therapy

Corticosteroids are commonly used when the developmental or cognitive impact is substantial and the sleep EEG remains severely activated.

Regimens differ internationally, and potential adverse effects require close medical supervision.

Epilepsy surgery

When a focal or hemispheric structural abnormality appears to drive the sleep-activated epileptic network, resective or disconnective surgery may be considered even when the EEG looks widespread.

A 2024 systematic review and meta-analysis found that carefully selected children undergoing surgery could achieve seizure improvement, resolution of the SWAS pattern and neuropsychological benefit.

Why a generalised-looking EEG does not always rule out surgery

Generalised sleep discharges can be generated by a focal structural network and spread rapidly through both hemispheres.

That is why MRI, PET/SPECT where appropriate, neuropsychology and specialist presurgical evaluation can remain relevant.

Outcome

The intense sleep EEG abnormality often improves with age, but developmental or cognitive deficits may persist after the EEG becomes less active.

Earlier recognition and successful suppression of the pathological network are therefore considered important, even though the exact treatment strategy remains uncertain.

Worldwide access

D/EE-SWAS is particularly vulnerable to underdiagnosis in regions without overnight EEG, paediatric neuropsychology, MRI or specialist epilepsy services.

A child may be labelled as having behavioural deterioration or school failure without anyone recognising that sleep EEG has become profoundly abnormal.

The central point

D/EE-SWAS is not simply “lots of spikes during sleep”. It is a syndrome in which sleep-activated epileptic activity is linked with developmental, cognitive, language, behavioural or motor deterioration, and the treatment target includes protecting function as well as controlling visible seizures.

Sources

Medical note: developmental regression in a child with epilepsy warrants prompt specialist assessment and sleep EEG where available.

Evidence checked: September 2026.