The presentation, course and outcome of Landau-Kleffner syndrome (LKS) were studied in 18 children (11 girls, 7 boys) followed for a mean of 67 months at Guy’s Hospital, London, UK. All showed receptive language regression and electrical status epilepticus in sleep (ESES). Mean age at onset was 4 years 9 months (range 25-84 months). The length of ESES (mean 44 months) was correlated significantly with length of period between onset of illness and onset of recovery, with length of daytime EEG abnormalities, seizure frequency, and period of seizures (mean 36 months). The correlation between language outcome and seizure activity was weaker than that with ESES. Receptive language outcomes for those whose ESES lasted <3 years was significantly better than those with ESES for >3 years. Behavior problems (ADHD and ODD) were common (50%), especially in patients with frontal lobe EEG abnormalities. Behavior abnormality in the acute phase was not correlated with seizure frequency, length of ESES, length of daytime EEG abnormality, nor with subsequent language outcome; there was a mild association with lower IQ All children had impaired short-term memory at follow-up. Recovery began at a mean age of 106 months, and the mean duration of acute involvement was 50 months. Receptive and expressive language outcomes were strongly correlated, but language and IQ measures showed weaker associations. Language outcome was normal in three. In children with ESES lasting longer than 36 months, none had normal language outcome. Multiple subpial transection should be considered if steroids are ineffective in the resolution of ESES by 36 months. 
COMMENT. In children with LKS the strongest predictor of outcome is the length of ESES. Those with recovery of language function have ESES for less than 3 years. Evolution of the syndrome is in 3 phases: 1) acute (few days to weeks) deterioration of receptive language with secondary deterioration in speech, seizures, mild behavior disturbance, centrotemporal EEG abnormalities awake and ESES in sleep; 2) chronic phase of aphasia and EEG abnormality lasting 1 to 7 years (mean 4 years), fluctuating seizures and worsening behavior disorder; and 3) stage of spontaneous improvement, occurring at a mean of 5 (range 1-9) months after resolution of ESES. Majority are left with various degrees of language impairment, particularly a verbal auditory agnosia, and full recovery is rare. Severe behavior problems (ADHD and ODD) are a common component of the syndrome and may be associated with frontal EEG abnormalities. AEDs are rarely effective and ESES is suppressed by steroids in only a minority of cases. Surgical intervention should be considered before ESES has persisted for >3 years.
Multiple subpial transection in LKS. Five children, aged 5-10 years, with LKS were treated surgically with multiple subpial transection at Guy’s Hospital, London, UK . Behavior, seizure frequency, and to a lesser degree language, improved dramatically after surgery in all patients treated. ESES was eliminated by the procedure. The timing of this intervention and its effect on language outcome needs further clarification.