Definition of Seizure
A seizure is defined as a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain 1.
Core Characteristics
The definition established by the International League Against Epilepsy (ILAE) emphasizes several key features:
- Transient nature: Seizures are brief, self-limited episodes
- Neuronal dysfunction: Results from abnormal excessive or synchronous neuronal activity in the brain
- Clinical manifestations: Can present as involuntary movements affecting part or all of the body, sometimes accompanied by loss of consciousness and sphincter control 2
Distinction from Epilepsy
It is critical to understand that not all individuals with seizures have epilepsy 3. The ILAE defines epilepsy as requiring one of the following 1:
- At least two unprovoked seizures occurring more than 24 hours apart
- One unprovoked seizure with a probability of further seizures similar to the general recurrence risk after two unprovoked seizures (occurring over the next 10 years)
- Diagnosis of an epilepsy syndrome
Classification of Seizures
Seizures are categorized based on their origin 1:
- Focal onset: Arising within networks of a single cerebral hemisphere, may remain localized or become more widely distributed
- Generalized onset: Rapidly affecting both hemispheres and both sides of the body
- Unknown onset: When the origin cannot be determined
Types of Seizures by Etiology
Acute Symptomatic Seizures
These occur at the time of a systemic insult or in close temporal association with a documented brain insult 4, 3. Common causes include:
- Traumatic brain injury
- Cerebrovascular disease
- Drug withdrawal
- Metabolic derangements
- Active CNS infection
Unprovoked Seizures
Seizures occurring in the absence of precipitating factors, which may be caused by static injury (remote symptomatic) or progressing injury (progressive symptomatic) 3.
Clinical Pitfalls
Avoid overdiagnosis: There is a documented tendency to overdiagnose epilepsy and excessive use of anticonvulsant drugs 2. Conditions frequently confused with seizures include:
- Syncope
- "Daydreams" (absence-like episodes)
- Functional seizures (pseudoseizures)
The classification system is operational rather than mechanistic, as the fundamental mechanisms of epileptic seizures have not been fully elucidated 1.