Stimulus-induced bilateral central periodic discharges, cortical myoclonus and arousal responses in mild reversible coma

Objective: To study the association between stimulus-induced periodic epileptiform discharges (PEDs), arousal EEG responses and limb jerking in a comatose patient with reversible viral encephalitis. Methods: We recorded video EEG in Intensive Care Unit (ICU) for strictly clinical purposes. Back averaging was performed off-line using Neuroscan 4.3. Results: We recorded spontaneous and stimulus-induced bilateral central PEDs (bi-central PEDs) that were followed by phasic vertex potentials, customarily considered as EEG arousal responses. Bi-central PEDs were associated with myoclonus when provoked by strong and protracted stimuli, but remained subclinical when elicited by auditory or mild tactile stimuli. Spontaneous and stimulus-induced bi-central PEDs disappeared after full neurological recovery. Conclusion: These findings link stimulus-induced PEDs to epileptic cortical myoclonus, and further suggest that in certain comatose patients they may represent reflex epileptic activity, even when clinically silent. The term "reflex seizures of the critically ill" may be appropriate in such patients. Our findings may also provide a model of the reciprocal relationship between arousals and epileptiform activity. Significance: Consideration of the possibility that stimulus-induced PEDs are reflexive epileptic phenomena in some comatose ICU patients may rationalise further their acute management, including antiepileptic treatment.