Epilepsy Definition
Epilepsy is defined as recurrent unprovoked seizures, specifically requiring either at least two unprovoked seizures occurring more than 24 hours apart, one unprovoked seizure with a probability of recurrence ≥60% over the next 10 years, or diagnosis of an epilepsy syndrome. 1, 2, 3
Core Diagnostic Criteria
The International League Against Epilepsy (ILAE) established three pathways to diagnose epilepsy:
- Two or more unprovoked seizures separated by more than 24 hours 2, 3
- One unprovoked seizure with a high probability (≥60%) of recurrence over the next 10 years 2, 3
- Diagnosis of a specific epilepsy syndrome based on characteristic clinical and electroencephalographic features 2
What Constitutes a 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, 2. This represents the intermittent and self-limited clinical manifestations resulting from abnormally excessive and synchronous neuronal activity 4.
Critical Distinction: Unprovoked vs. Provoked Seizures
Unprovoked seizures occur without acute precipitating factors and define epilepsy—they indicate an enduring predisposition to generate seizures 5, 3. These include remote symptomatic seizures resulting from a CNS or systemic insult that occurred more than 7 days in the past 5.
Provoked seizures (also called acute symptomatic seizures) occur at the time of or within 7 days of an acute neurologic, systemic, metabolic, or toxic insult 5. These do NOT constitute epilepsy, as they represent a natural response of the normal brain to transient noxious insults 6.
Important Clinical Pitfalls
- A single seizure does not equal epilepsy unless there is documented high recurrence risk (≥60% over 10 years) or an identified epilepsy syndrome 3
- Isolated provoked seizures from metabolic causes (hyponatremia, hypocalcemia, hypoglycemia), medications (tramadol), or acute brain injury should not be labeled as epilepsy 5
- Reactive seizures occurring within 7 days of stroke, trauma, infection, or metabolic derangement are excluded from the epilepsy definition 5, 6
Epidemiology and Impact
Epilepsy affects approximately 1.2% of the US population (3.4 million people) and 50 million people worldwide 2. An estimated 2% to 5% of the population will have at least one nonfebrile seizure during their lifetime, but only those meeting the criteria above are diagnosed with epilepsy 1.
What Epilepsy Is NOT
Epilepsy is not a single disease but rather a heterogeneous group of disorders sharing the characteristic of recurrent, usually unprovoked seizures 4. It encompasses specific etiology, associated neurologic abnormalities, genetic background, environmental factors, and responses to therapies 4. The disability and effect on quality of life vary significantly for each individual 4.