Unihemispheric burst suppression

Abstract

Burst suppression (BS) consists of bursts of high-voltage slow and sharp wave activity alternating with periods of background suppression in the electroencephalogram (EEG). When induced by deep anesthesia or encephalopathy, BS is bihemispheric and is often viewed as a non-epileptic phenomenon. In contrast, unihemispheric BS is rare and its clinical significance is poorly understood. We describe here two cases of unihemispheric BS. The first patient is a 56-year-old woman with a left temporoparietal tumor who presented in convulsive status epilepticus. EEG showed left hemispheric BS after clinical seizure termination with lorazepam and propofol. The second patient is a 39-year-old woman with multiple medical problems and a vague history of seizures. After abdominal surgery, she experienced a convulsive seizure prompting treatment with propofol. Her EEG also showed left hemispheric BS. In both cases, increasing the propofol infusion rate resulted in disappearance of unihemispheric BS and clinical improvement. The prevailing view that typical bihemispheric BS is non-epileptic should not be extrapolated automatically to unihemispheric BS. The fact that unihemispheric BS was associated with clinical seizure and resolved with propofol suggests that, in both cases, an epileptic mechanism was responsible for unihemispheric BS.

Keywords: burst suppression; electroencephalogram; propofol; seizure; status epilepticus; unihemispheric.

Figure 1.

Electroencephalogram of Patient A showing left-sided burst suppression 45 minutes after status epilepticus termination with fosphenytoin 1000 mg, lorazepam 4 mg, and propofol 2 mg/kg load. The occasional right-sided sharp waves that stand out against the low-amplitude slow background activity are most likely the result of volume conduction from the left hemisphere source. Unihemispheric burst suppression persisted as propofol was being infused at 2 mg/kg/hr and disappeared 4 hours later when the infusion rate was 5 mg/kg/hr. Propofol was discontinued after 12 hours with no recurrence of seizure activity and uni-hemispheric burst suppression.

Figure 2.

Electroencephalogram of Patient B showing left-sided burst suppression 30 minutes after clinical seizure termination with intravenous levetiracetam 1000 mg and propofol 2 mg/kg load. Fragments of burst activity, spilling over the right hemisphere are most likely due to volume conduction from the left hemisphere source. Unihemispheric burst suppression was present during propofol infusion at 2 mg/kg/hr. It disappeared 2 hours later when the propofol infusion rate was 5 mg/kg/hr. Propofol was discontinued after 18 hours with no recurrence of seizure and unihemispheric burst suppression.