Polysomnographic assessment of epileptic state: a dynamic mode.

Dear Editor, Epilepsy is a clinical diagnosis. Electroencephalography (EEG) has remained the most important investigative tool to provide supportive evidence and other characteristics in diagnosing and classifying the epileptic state. However, a routine EEG is insufficient to assess the epileptic state, especially with the ongoing, dynamic nature of the epileptic disorder. More important, a routine EEG fails to comment on the severity or future course of the epileptic state, especially regarding possible progress toward intractability, that occurs in as many as one-third of patients. Anecdotal experiences (including the author's) claim that the EEGs of patients with severe or intractable epilepsy are not significantly different in either background or paroxysmal (especially interictal) activity from EEGs of patients who respond to medication. Advances in neu-roimaging have also failed to provide superior assessment of the epileptic state in comparison with routine EEG. Furthermore, there have been no findings pertaining to the dynamic nature of epilepsy. This letter presents a novel approach to a comprehensive assessment of an epileptic state, which may also aid in understanding its ongoing nature. Sleep and epilepsy are known to bear an inherent, intricate , and complex relation with one another; sleep influences the epileptic state and vice versa. There is robust literature that non–rapid eye movement (NREM) sleep increases seizure susceptibility (excitatory or proepileptic influence), whereas rapid eye movement (REM) sleep increases seizure resistance (inhibitory or antiepileptic influence). In keeping with this ideology, REM sleep deprivation is associated with increased cortical excitability 2 and increased proepileptic influence. 3-5 As a general mechanism, epileptic activation during NREM sleep has been found to be linked to phasic activation of reactive delta bursts, which is believed to hold a global relation to sleep, valid for almost all epilepsies. 6 REM sleep is also reduced in several forms of intractable epilepsy, 7 and its restoration or enhancement contributes to the therapeutic efficacy of alternative therapies, such as ketogenic diet, 8 vagal nerve stimulation, 9 and temporal lobe surgery, 10 in intractable epilepsy. Based on this strong clinical relation between REM sleep and intractable epilepsy, REM sleep has been proposed as a biomarker of intractability in epilepsy. 11 Polysomnography (PSG) has been suggested as a superior investigative tool compared with EEG in assessment of the epileptic state. 12 Thus, it can be postulated that seizure susceptibility , and/or severity, bears an explorable relation with reduction or disruption of REM sleep. In keeping with …