In most patients with Landau-Kleffner syndrome (LKS), epileptiform abnormalities increase during sleep. The pattern of continuous spikes and waves during slow sleep (CSWS) is relatively frequent. For example, in a series of 17 LKS patients reported by da Silva et al.,52 7 patients had CSWS, as did almost half of the patients with LKS or one of its variants in another study.34
When first described, CSWS was called electrical status epilepticus during sleep.56 This term has been supplanted by CSWS because patients with electrical status epilepticus during sleep do not necessarily have epilepsy and because the presence of clinical status epilepticus cannot be demonstrated during sleep. It also is known as continuous spike-wave discharges during sleep (CSWDS).
Some investigators consider CSWS to be a syndrome in its own right, one that lies along the same spectrum as LKS and shares a similar pathophysiology.57,58 Bureau59 has reviewed and mapped the natural history of the CSWS syndrome. The first seizure generally occurs between ages 1 and 10 years, with a peak at 4 to 5 years. In about half the patients, this is a hemiclonic seizure, which frequently is prolonged. Other seizure types also are seen, mostly during sleep. The initial EEG reveals a multifocal spike and slow wave pattern or a diffuse spike and wave pattern. The EEG abnormalities worsen during sleep. In nearly two-thirds of patients, development is normal. The other one-third experience delays, predominantly in language. In nearly one-third, brain abnormalities can be demonstrated on imaging.
During the CSWS period, seizure characteristics change, as atypical absence seizures (including status epilepticus) and atonic seizures begin to predominate and epilepsy becomes severe. Tonic seizures have never been reported. A diffuse spike and wave pattern appears on the awake EEG. CSWS appears during non–rapid eye movement (non-REM) sleep (present for more than 85% of the time) and may continue for months to years. The exact age of onset and duration of CSWS can be difficult to determine clinically, as knowledge of these features depends on the timing of the EEG. The average age for diagnosis is 8 years.
Previously normal children deteriorate (leading to a diagnosis of LKS, autistic epileptiform regression, or disintegrative epileptiform disorder, depending on the clinical features), and previously delayed children regress. In the third phase of CSWS syndrome, epilepsy remits and CSWS disappears. At least half of the patients remain significantly impaired, however. The duration of CSWS on the EEG appears to affect prognosis.
In a comprehensive literature review of 209 patients with CSWS on EEG, Rousselle and Revol53 differentiated three main clinical groups based on neuropsychological profile during the period when CSWS was present. This profile correlated directly with the duration of CSWS and the site of the main epileptogenic focus:
Reviewed and revised May 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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