This chapter focuses on several of the most common actionable EEG abnormalities. This includes defining and describing epileptiform discharges, which are abnormal EEG waves that serve as markers of increased seizure risk. This also includes seizures themselves, and their characteristics and electrographic criteria. Prolonged and repetitive seizures known as status epilepticus are described, including their specific electrographic characteristics and criteria. The treatment resistant form of status epilepticus known as refractory status epilepticus is also described. Finally, the chapter describes a high risk electrographic phenomenon known as brief potentially ictal rhythmic discharges (BIRDs).

This chapter describes recognizing seizures, brief potentially ictal rhythmic discharges (BIRDs), and sporadic epileptiform discharges using a case-based approach. Electrographic seizures are patterns 10 seconds or longer of epileptic activity occurring at >2.5 Hz or other evolving patterns. If these patterns are associated with a clinical correlate, they are called electroclinical seizures, even if they are less than 10 seconds in duration. A high seizure burden may be associated with neurological decline. Patterns of rhythmic activity too short to qualify as seizures are termed BIRDs. Sporadic epileptiform discharges such as spikes or sharp waves are associated with increased seizure risk and epilepsy. Epilepsy itself is a clinical diagnosis of recurrent and unprovoked seizures.

Ictal patterns represent ongoing electrographic seizures. They are recognized by their clinical accompaniments (may be subtle) and electrographic features. Evolution is the electrographic hallmark of an ictal pattern, plus features (such as overriding fast activity) also render a pattern more ictal in appearance. Electrographic seizures will typically have a clear onset, evolution and offset. Conventionally, they should last for greater than 10 seconds. Electrographic seizures are common in after convulsive seizures, acute brain injury and in critically ill patients with altered mentation. Continuous EEG monitoring is the preferred method of diagnosing electrographic seizures. Typically, a duration of 24 hours is sufficient, but this should be extended in certain high-risk populations.