A condition characterized by continuous spikes and waves occurring during sleep was described in 1971 under the name of subclinical electrical status epilepticus induced by sleep in children and later under the name of electrical status epilepticus during sleep.68 The original description stressed the importance of defining the syndrome by the amount of spike-wave activity during sleep. To meet the requirements of the syndrome, spike-wave activity should occupy no less than 85% of the time of slow sleep. Consequently, this syndrome also is known as continuous spike-wave discharges during sleep (CSWDS).
In one series of 18 patients,68,69 epilepsy appeared at a mean age of 4 years, 6 months. The types of clinical seizures varied:
- unilateral seizures (5 patients)
- generalized motor seizures (8 patients)
- motor seizures involving the facial muscles, with mandibular contraction and loss of consciousness (4 patients)
- myoclonic absences (1 patient)
In half these patients, the first seizure occurred during sleep.
In another series of 5 children, 3 atypical absence seizures and partial seizures were observed.
The syndrome can be differentiated from Lennox-Gastaut syndrome (LGS) by the total amount of sleep occupied by spike-wave discharges. In children with CSWDS, generalized spike-wave activity occurs during more than 85% of sleep time, versus less than 50% in LGS. Another difference is that tonic seizures, which are so common in LGS, are rare in children with CSWDS.68,70
Comparisons to Landau-Kleffner syndrome
There appears to be an overlap between CSWDS and the Landau-Kleffner syndrome. Of 18 children in one series, 11 who were normal before the development of CSWDS experienced a decrease in IQ ranging from 45 to 78 points.69 A very marked reduction in language function occurred in 6 children. In 10 cases, disturbances in behavior were found, including decreased attention, hyperactivity, and aggressiveness. In 7 children who had abnormal psychomotor development before the onset of CSWDS, their mental deficiency worsened. Deterioration in behavior and speech after the onset of CSWDS was also observed in the 5 children in the other series.70
Hirsch et al71 reported on five children in whom the Landau-Kleffner syndrome developed when they were between the ages of 3 and 7. The EEG in the wake state demonstrated focal and generalized spike-wave activity on a normal background. During sleep the discharges always increased. At some point during the development of the syndrome, the patients had bilateral spike-wave activity lasting for more than 75% of their sleep time. The authors suggested that the Landau-Kleffner syndrome and this syndrome represent different points on a single spectrum.
In 6 children with subclinical "electrical status epilepticus" during sleep, the electrical status subsided during REM sleep in 5.71 All of the children were mentally retarded, and 2 failed to acquire speech.
As with the Landau-Kleffner syndrome, variable improvement may occur in affected children as CSWDS resolves.68,70 In one series,68 7 of the 11 children who were normal before the onset of CSWDS improved in performance, behavior, or both after it resolved. Two totally recovered and the others showed a slight degree of recovery.
Adapted from: Holmes GL. Classification of seizures and the epilepsies. In: Schachter SC, Schomer DL, eds. The comprehensive evaluation and treatment of epilepsy. San Diego, CA: Academic Press; 1997. p. 1-36.
With permission from Elsevier (www.elsevier.com)