Electroencephalographic Findings

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The EEG features of this syndrome may be separated into those before ESES and those during ESES.

Before ESES

In the series reported by Tassinari et al. (1985, 1992b), at least one waking EEG was available in each patient after the first clinical manifestation. The background activity was either normal or abnormal. Eleven patients had more or less generalized SWs, sometimes in bursts, clinically with or without an impairment of consciousness with twitching of the eyelids. Thirteen patients had focal interictal spikes, localized over the frontotemporal or centrotemporal regions with or without diffuse abnormalities. In five cases, there were focal or multifocal abnormalities without any generalized discharge. In the same group of patients, sleep recordings were performed in eight cases and showed an increase of the interictal abnormalities, without change in morphology and without alteration of sleep. Morikawa et al. (1985) also reported similar findings in waking EEGs before ESES onset.

During ESES

The interictal abnormalities during wakefulness are similar to those before ESES, but are usually more marked. Tassinari et al. (1985, 1992b) emphasized the occurrence of diffuse SW at 2-3 Hz, organized in bursts with or without clinical manifestations. Morikawa et al. (1989) analyzed the clinical correlates of these diffuse bursts by simultaneous closed-circuit TV-EEG and found out that there were concomitant clinical correlates in only a limited number of patients. More or less prolonged bursts of diffuse slow SW complexes during wakefulness were also reported in 49 of the 73 ESES cases discussed during the Venice Colloquium (Beaumanoir, 1995b). In the same series, a parallel was demonstrated between the diffuse slow SW percentage during wakefulness and the SW index during sleep.

The characteristic feature of this disorder obviously occurs during nonrapid eye movement (NREM) sleep. As soon as the patients fall asleep, continuous bilateral and diffuse slow SWs appear, mainly at 1.5-2 Hz, persisting through all the slow sleep stages (Fig. 9.1). This pattern is generally found between the ages of 4 and 14 years and seems to develop 1 or 2 years after the appearance of seizures. Tassinari et al. (1982, 1985, 1992a,b) stressed the importance of the SW index, which was calculated during all night sleep EEG recordings. In the Marseille series, the SW index ranged from 85 to 100% and this parameter was considered an essential feature for the diagnosis of ESES. The same parameter was adopted by Morikawa et al. (1985, 1992), Boel and Caesar (1989), Hirsch

AWAKE DROWSINESS SLOW SLEEP

FIGURE 9.1 Awake recording (left), showing focal spikes. Drowsiness (middle) provokes the appearance of spike and wave discharges, which become continuous during NREM or slow sleep (right). (From Tassinari et al., 1985, with permission.)

FIGURE 9.1 Awake recording (left), showing focal spikes. Drowsiness (middle) provokes the appearance of spike and wave discharges, which become continuous during NREM or slow sleep (right). (From Tassinari et al., 1985, with permission.)

et al. (1990), Bureau et al. (1990), and Yasuhara et al. (1991) to define the ESES syndrome. Other authors, however, criticized this view and applied the term "ESES" even if the SW index was under 85%, (Calvet, 1978; Billard et al., 1982). Beaumanoir (1995b) reviewed the sleep EEG data of the new cases labeled as ESES presented during the Venice Colloquium and found that an SW index of at least 85% was reached in 64% of the observations. He separated the patients into two groups according to the SW index and found that 27% of patients belonging to the group with an SW index below 85% did not present a significant drop in their performance scores.

Other relevant features of ESES concern the morphology and distribution of the paroxysms during slow-wave sleep. In the original series (Tassinari et al., 1982, 1985, 1992b; Morikawa et al., 1985), ESES was described as consisting of generalized or "diffuse" slow SWs at 1.5-2 Hz. However, cases displaying slow spikes devoid of the wave component (Michelucci et al., 1987) or sharp waves (Fulgham et al., 1990) have been reported. Moreover, cases with relatively focal, albeit continuous, discharges mainly involving the temporal or frontal regions or markedly asymmetrical SW activity over the two hemispheres have been described (Billard et al., 1982; Morikawa et al., 1985; Michelucci et al., 1987; Veggiotti et al., 1999).

Typically the paroxysmal activity becomes less continuous and the SW index is under 25% in rapid eye movement (REM) sleep; however, the focal discharges, predominantly frontal in location, may become prominent during REM sleep. In general, the EEG patterns during REM sleep are similar to those in the awake record. Finally, ESES disappears as abruptly on awakening as it appears at sleep onset.

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