Generation Of Epileptic Discharges

FIGURE 8.8 Schematic representation of the interplay between generators of epileptic discharges and thalamocortical circuits. In primary generalized epilepsy (PGE), the epileptic activity is closely related to the thalamocortical pathways. The focal Iesional (FL) spiking involves an intermediate position between the thalamus and the cerebral cortex, while the functional rolandic bursts (BERS) are confined in a far-field cortical position.

FIGURE 8.8 Schematic representation of the interplay between generators of epileptic discharges and thalamocortical circuits. In primary generalized epilepsy (PGE), the epileptic activity is closely related to the thalamocortical pathways. The focal Iesional (FL) spiking involves an intermediate position between the thalamus and the cerebral cortex, while the functional rolandic bursts (BERS) are confined in a far-field cortical position.

subtype is determined, it can be noticed that there is a striking preference for the portions characterized by EEG synchrony. In effect, the EEG paroxysms tend to occur throughout the entire length of subtypes A1 (totally expressed by EEG synchronized patterns), while the IIDs are mostly concentrated in the initial portions of the A2 and in the A3 subtypes that almost invariably start with a K-complex or a delta burst.

The activating power of EEG synchrony is also confirmed by the distribution of IID within the different segments of the sleep cycle. Although the descending branches (prevalence of A1 subtypes) and the ascending branches (prevalence of A2 and A3 subtypes) express equivalent levels of arousal instability (CAP rates: 48 and 44%, respectively), the CAP-related percentages of ID are significantly higher during deepening compared with lightening sleep (67 versus 31%;/? < .03).

cyclic alternating pattern and nocturnal motor seizures

Although the continuum from subclinical EEG paroxysms to clinical seizures is still incompletely understood, there is, however, general agreement on the assumption that sleep instability facilitates both interictal and ictal phenomena. The close relationship between CAP and spike occurrence actually finds an extensive confirmation in sleep-related seizures. In a study conducted on patients affected by focal epilepsy, 43 of 45 nocturnal partial motor seizures occurred during NREM sleep (Terzano et al., 1991a). Among the NREM seizures, 42 appeared in CAP (p < .0001) and always during a phase A (Fig. 8.9). An investigation confirmed that 83% of temporal lobe seizures recorded in stage 2 NREM sleep occurred during CAP with a predominant activating action manifested by phase A (Arunkumar et al., 1997).

In patients with nocturnal paroxysmal dystonia (NPD) characterized by repeated episodes of abnormal stereotyped movements (dystonic-dyskinetic) with duration mostly 10-60 s, motor events are closely related to periods of unstable sleep, as evidenced by the CAP sequences (Fig. 8.10), and occur during an A phase (Sforza et al., 1993; Terzano et al., 1997). NPD recordings are characterized by prolonged and irregular sleep cycles and by significantly higher values of CAP rate compared with normal controls. After effective medication (carba-mazepine), sleep showed decreased amounts of CAP rate and a more regular architecture (Terzano et al., 1997).

Confirming that seizure manifestations are strictly connected to fluctuations of arousal (Shouse et al., 1989), these findings also suggest a direct relationship between CAP and motor events. In addition to epileptic manifestations, CAP can trigger other motor activities from physiological body movements to nocturnal myoclonus (Parrino et al., 1996), sleep bruxism (Macaluso et al., 1998), night terrors, and sleepwalking (Zucconi et al., 1995). The definition of clear-cut boundaries between physiological and pathological movement patterns is in progress (Zucconi et al., 1997), while promising results are supplied by the genetic investigation of patients with exclusive nocturnal seizures (Scheffer et al., 1995; Oldani et al., 1998). It is known that the number and distribution of nocturnal movements is a personal characteristic of the sleeper, who is endowed with a given pool of opportunities for the accomplishment of motor episodes

0 0

Post a comment