What is the role of Electroencephalography (EEG) in diagnosing and managing seizure disorders, such as epilepsy?

Role of Electroencephalography (EEG) in Diagnosing and Managing Seizure Disorders

EEG is the definitive diagnostic test for detecting seizure activity and is essential for diagnosing epilepsy, identifying seizure types, monitoring treatment response, and detecting nonconvulsive seizures that would otherwise be missed by clinical observation alone. 1

Diagnostic Applications of EEG

Epilepsy Diagnosis

• EEG is the most specific method to define epileptogenic cortex, with sensitivity and specificity dependent on factors such as age and recording procedures 2
• EEG reveals characteristic findings in several epilepsy syndromes, helping to classify the type of epilepsy which guides treatment decisions 3
• A normal interictal EEG does not rule out epilepsy and must always be interpreted in a clinical context 4
• EEG can help differentiate seizures from other conditions that mimic seizures, such as syncope, when clinical data are equivocal 4

Seizure Classification

• EEG findings are crucial for the classification of seizures and epilepsy syndromes 1
• Classification of seizure type enables identification of the brain region where the seizure originated and guides initial diagnostic testing 3
• Ictal video/EEG recording is considered critical in localizing the epileptogenic zone 2

Detection of Nonconvulsive Seizures

• EEG is recommended in all patients with acute brain injury and unexplained persistent altered consciousness 4
• Nonconvulsive status epilepticus can present as acute confusional states, behavioral changes, or encephalopathy that would be missed without EEG 4
• Routine EEG (typically 30 minutes) will miss nonconvulsive seizures in approximately half of patients with seizures compared to prolonged monitoring 4

Specific Clinical Scenarios for EEG Use

Status Epilepticus

• Emergent EEG is recommended in patients suspected of being in nonconvulsive status epilepticus or subtle convulsive status epilepticus 4
• EEG should be used in patients who have received a long-acting paralytic or are in a drug-induced coma 4
• A recent trial examining treatments for generalized convulsive status epilepticus found that 25% of patients had evidence of continuing electrical seizures when generalized convulsive status epilepticus was present 4

Autoimmune Encephalitis

• EEG can provide evidence of focal or multifocal brain abnormality when MRI is negative, supporting encephalitis over metabolic encephalopathy 4
• Findings suggestive of autoimmune encephalitis include focal slowing/seizures, lateralized periodic discharges, and extreme delta brush (occasionally seen in NMDAR-antibody encephalitis) 4
• A normal EEG does not exclude autoimmune encephalitis but can support primary psychiatric disorders when investigating patients with isolated new psychiatric symptoms 4

Post-Seizure Evaluation

• EEG is recommended when patients do not return to functional baseline within 60 minutes after convulsive status epilepticus 4
• An altered level of consciousness after a motor seizure may be due to nonconvulsive status or subtle convulsive status epilepticus, which can only be detected by EEG 4

EEG Monitoring Approaches

Continuous vs. Routine EEG

• Continuous EEG monitoring is superior to routine EEG for detecting seizures in critically ill patients 4
• Continuous monitoring can detect cyclic seizure patterns that would be missed by routine recordings 4
• For acute encephalopathy with refractory, repetitive partial seizures, continuous EEG monitoring can reveal frequent subclinical seizures missed by direct observation 5

Invasive EEG Monitoring

• Invasive EEG recordings are used when the epileptogenic zone cannot be located with noninvasive methods or is adjacent to eloquent cortex 2
• Common invasive electrodes include stereotactically implanted depth electrodes and subdural strip or grid electrodes 2
• Invasive EEG is essential for planning epilepsy surgery in selected patients 1

Practical Considerations and Limitations

Timing and Access

• The average response time from request to initial EEG reading is approximately 3 hours, which exceeds ideal availability for treatment of time-critical conditions 4
• Most facilities require neurologic consultation before emergent EEG can be obtained 4
• Local access to neurologic and EEG expertise, technical personnel, and equipment will likely continue to limit performance of EEGs in emergency departments 4

Interpretation Challenges

• EEG interpretation is a specialized province within neurology, making neurologic consultation before obtaining an EEG reasonable 4
• Quantitative EEG algorithms have been developed to support the time-consuming expert review of continuous EEG recordings in the ICU setting 4
• Bispectral index score (BIS) measurements are not recommended for brain-injured patients due to large intra- and inter-individual variability 4

Common Pitfalls to Avoid

• Failing to obtain an EEG in patients with altered consciousness who may have nonconvulsive status epilepticus 4
• Relying solely on routine EEG when continuous monitoring would be more appropriate for detecting seizures 4
• Misinterpreting normal EEG findings as ruling out epilepsy 4
• Using EEG when syncope is the most likely cause of transient loss of consciousness 4
• Placing invasive electrodes without exhaustive noninvasive evaluations, as they are subject to sampling errors if misplaced 2