cEEG monitoring provides independent prognostic information in patients with poor-grade SAH, even after controlling for clinical and radiological findings. Unfavorable findings include periodic epileptiform discharges, electrographic status epilepticus, and the absence of sleep architecture.

We propose a comprehensive review of the subject of epileptiform and potentially harmful EEG patterns that lie on the interictal continuum (IIC) to help with therapeutic decision-making and target future research. This approach to "electro-physiological SE" encompasses five dimensions of the IIC: it characterizes a periodic or rhythmic pattern, not only regarding its ictal morphology and potential harm with secondary neuronal injury, but also addresses the "metabolic footprint," clinical repercussion, and epileptogenic potential. Recent studies have attempted to determine and qualify the ictal nature and the epileptogenic potential (i.e., risk of subsequent acute seizures) of particular IIC patterns and their intrinsic EEG characteristics. Others have correlated non-convulsive seizures with cognitive outcomes beyond mortality; non-convulsive seizures and sporadic, periodic, or rhythmic discharges to encephalopathy severity; and the spectrum of periodic or rhythmic patterns to measurable secondary brain injury. Equivocal periodic or rhythmic patterns on the IIC are frequently encountered in critical care neurology where clinicians often incorporate advanced neuroimaging, metabolic neuromonitoring, and anti-seizure drug short trials, in an effort to gauge these patterns. We propose portraying the IIC with a multiaxial graph to disambiguate each of these risks. Quantification along each axis may help calibrate therapeutic urgency. An adaptable scoring system assesses which quasi-ictal EEG patterns in this spectrum might reach the tipping point toward anti-seizure drug escalation, in neurocritically ill patients.

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