A prospective study of levetiracetam efficacy in epileptic syndromes with continuous spikes-waves during slow sleep. 
To evaluate the add-on effect of levetiracetam (LEV) treatment on the EEG and clinical status of children with continuous spikes-waves during slow sleep (CSWS).  20 children with CSWS refractory to other conventional antiepileptic drugs (AEDs) received LEV 45-50 mg/kg/day as add-on treatment, and were prospectively followed for a minimum period of 18 months.  The patient population comprised seven cryptogenic, seven symptomatic and six idiopathic cases (atypical benign partial epilepsy, aBECTs).  The electrographic evaluation included 24 h EEG recordings taken every six months (minimum of three per child).  Electrographically children were categorised as responders, partial responders or non-responders by comparing changes in the spike index (SI) during NREM-sleep with baseline SI before initiation of LEV.  The clinical efficacy of LEV was assessed by comparing seizure frequency at the end of follow up with the baseline.  The follow up duration varied from 18 to 53 months.  Electrographic response was observed in 11 patients.  Eight patients demonstrated a lasing response (more than 12 months): five from symptomatic, two--cryptogenic and one--idiopathic group respectively.  Three children showed a partial response (6-12 months): one from symptomatic and two from idiopathic group.  Eleven out of the 20 children were seizure free at baseline and during the whole follow up.  The rest, six-symptomatic and three-cryptogenic patients, had seizures prior to LEV treatment initiation.  Six became seizure free after add-on therapy with LEV, and in three children a significant reduction of seizure frequency was observed.  This study suggests that add-on therapy with LEV is more effective in children with CSWS resulting from a known underlying structural brain lesion (the symptomatic group).