Landau–Kleffner syndrome is a rare childhood epileptic encephalopathy characterised by acquired language regression associated with epileptiform EEG abnormalities, often markedly activated by sleep.
The key feature is acquired language loss
A child who had previously developed language can lose comprehension, expressive language or both.
The change may initially be mistaken for hearing loss, autism, behavioural difficulty or developmental regression from another cause.
Seizures may be absent or infrequent
Clinical seizures occur in many but not all children.
The severity of language dysfunction can therefore be much greater than the visible seizure burden suggests.
Sleep EEG is important
Epileptiform discharges often increase substantially during non-REM sleep.
A short awake EEG may miss the relevant pattern, so sleep-containing EEG can be critical.
It overlaps with the spike-wave activation spectrum
Landau–Kleffner is related to the broader group now described as developmental and/or epileptic encephalopathy with spike-wave activation in sleep.
Language-predominant regression is the defining clinical emphasis.
Treatment targets both EEG and development
Antiseizure medicines, corticosteroid therapy and other interventions may be considered depending on the case.
Speech and language therapy and educational support remain essential even when EEG improves.
Related reading
Sources and further reading
Evidence checked: September 2026.