What are the three criteria for diagnosing epilepsy?

Three Criteria for Diagnosing Epilepsy

The International League Against Epilepsy (ILAE) defines epilepsy as meeting any one of three specific criteria: (1) at least two unprovoked seizures occurring more than 24 hours apart, (2) one unprovoked seizure with a probability of recurrence ≥60% over the next 10 years (similar to the risk after two unprovoked seizures), or (3) diagnosis of an epilepsy syndrome. 1, 2, 3

The Three Diagnostic Criteria Explained

Criterion 1: Two Unprovoked Seizures

• At least two unprovoked (or reflex) seizures must occur more than 24 hours apart 1, 2, 3
• This is the traditional and most straightforward criterion, providing high diagnostic certainty 3, 4
• The 24-hour separation distinguishes epilepsy from acute repetitive seizures or status epilepticus 3
• This criterion has been the historical standard and maintains consistency with past epidemiologic studies 4

Criterion 2: Single Seizure with High Recurrence Risk

• One unprovoked (or reflex) seizure AND a probability of further seizures ≥60% over the next 10 years 1, 2, 3, 5
• This criterion recognizes that certain clinical features predict high recurrence risk after a single seizure 3, 4
• Risk factors that increase recurrence probability to ≥60% include:
  • Structural brain lesions identified on neuroimaging 6
  • Epileptiform abnormalities on electroencephalography (EEG) 6
  • History of prior brain insult (stroke, trauma, infection) 7, 6
  • Specific imaging findings suggesting epileptogenic potential 6
• This criterion allows earlier diagnosis and treatment initiation in high-risk patients rather than waiting for a second seizure 3, 5

Criterion 3: Epilepsy Syndrome Diagnosis

• Diagnosis of a recognized epilepsy syndrome, even with a single seizure 1, 2, 3
• Epilepsy syndromes are defined by constellation of features including seizure type, age at onset, EEG patterns, imaging findings, and genetic factors 1, 7
• Examples include juvenile myoclonic epilepsy, childhood absence epilepsy, and other well-characterized syndromes 1
• Syndrome diagnosis provides insight into natural history, prognosis, and appropriate treatment selection 7

Important Clinical Distinctions

Unprovoked vs. Provoked Seizures

• Only unprovoked seizures count toward epilepsy diagnosis 3, 7
• Provoked (acute symptomatic) seizures occur due to acute brain injury, metabolic derangements, toxins, or other temporary factors 7, 6
• Provoked seizures are treated by addressing the underlying cause, not with chronic antiepileptic drugs 7

When Epilepsy is Considered Resolved

• Epilepsy is considered resolved (not necessarily cured) when patients have been seizure-free for 10 years AND off antiseizure medications for at least 5 years 3, 5
• Age-dependent epilepsy syndromes are considered resolved once the patient passes the applicable age range 3, 5

Clinical Application

The 2014 ILAE revision allows clinicians to diagnose epilepsy earlier in appropriate circumstances (Criterion 2) rather than waiting for a potentially dangerous second seizure 3, 5. This practical definition balances the need for diagnostic certainty against the risks of delaying treatment in high-risk patients 4, 6. The diagnosis carries significant medical, social, and emotional consequences, so it should be made with careful consideration of all three criteria 6.