From the Guidelines
Subclinical seizure activity is characterized by abnormal electrical discharges in the brain that do not produce noticeable symptoms, and can only be detected through electroencephalogram (EEG) monitoring, with the most recent definition and criteria established by the American Clinical Neurophysiology Society as referenced in the 2024 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations 1.
Definition and Criteria
The definition of subclinical seizure activity is crucial for accurate diagnosis and treatment. According to the 2024 consensus, terms such as electrographic seizure, electroclinical seizure, and electroclinical status epilepticus are defined based on specific EEG patterns and durations, providing a framework for identifying and managing subclinical seizures 1. For instance, an electrographic seizure is defined as epileptiform discharges averaging >2.5 Hz for ≥10 s, highlighting the importance of precise EEG interpretation.
Diagnosis and Monitoring
Continuous EEG monitoring is essential for detecting subclinical seizures, especially in high-risk patients such as those in intensive care settings or with a history of epilepsy. The use of continuous EEG allows for the early identification of abnormal electrical activity, enabling prompt intervention to prevent potential neurological damage 1. However, the cost-effectiveness and labor intensity of continuous EEG monitoring are considerations that must be weighed against the potential benefits of early detection and treatment.
Treatment and Management
Treatment of subclinical seizures typically involves antiepileptic medications, with the goal of suppressing abnormal electrical activity and preventing neurological damage. Medications such as levetiracetam, valproic acid, and lacosamide may be used, with the specific choice depending on the patient's medical history and condition. While there is evidence to support the effectiveness of these medications in suppressing epileptiform activity, the potential benefits and risks must be carefully considered, particularly in comatose post-cardiac arrest patients where the use of sedating agents may delay awakening 1.
Importance of Addressing Subclinical Seizures
Addressing subclinical seizures is crucial because persistent abnormal brain activity may contribute to neurological damage and cognitive decline if left untreated. Early detection and treatment can help prevent these outcomes, emphasizing the importance of continuous EEG monitoring and prompt intervention in high-risk patients. By prioritizing the management of subclinical seizures, healthcare providers can help mitigate the risk of long-term neurological consequences and improve patient outcomes.
From the Research
Definition and Characteristics of Subclinical Seizure Activity
- Subclinical seizures (SCSs) are characterized by paroxysmal rhythmic epileptiform discharges that evolve in time and space in the absence of objective clinical manifestation or report of a seizure 2.
- SCSs are often detected using continuous electroencephalography (cEEG) or intracranial EEG monitoring 3, 4, 5.
- The mean duration of SCSs is shorter than complex partial seizures and generalized tonic-clonic seizures but similar to simple partial seizures 4.
- SCSs rarely propagate beyond the site of origin and the majority of SCSs have the same area of origin as clinical seizures 4.
Clinical Significance and Impact on Surgical Outcome
- The presence of SCSs is not uncommon in children with localization-related epilepsy, particularly in younger children, those with developmental disability, and those with a medically refractory clinical course 2.
- The colocalization rate of SCSs and clinical seizures may impact seizure-free outcome after epilepsy surgery 4.
- However, the presence of SCSs was not associated with epilepsy surgical outcomes in some studies 5.
- Completeness of resection remains the most important predictor of seizure outcome, regardless of the presence of SCSs 5.
Patient Characteristics and Subclinical Seizure Activity
- Patient characteristics such as age, developmental delay, and history of infantile spasms are associated with the presence of SCSs in some studies 2.
- However, other studies found no significant patient characteristics associated with the presence of SCSs 5.
- SCSs are often captured in patients with refractory focal epilepsy, and they may provide useful localization information to guide surgical resection plans 5.