What is the difference between a diagnosis of epilepsy and a seizure?

Distinguishing Seizure from Epilepsy: Diagnostic Definitions

A seizure is a single transient event of abnormal brain activity, while epilepsy is a chronic disease defined by recurrent unprovoked seizures—specifically, at least two unprovoked seizures occurring more than 24 hours apart, or one unprovoked seizure with high probability of recurrence (≥60%), or diagnosis of an epilepsy syndrome. 1, 2

Core Definitional Differences

Seizure: The Acute Event

• A seizure represents a single episode of transient signs and/or symptoms caused by abnormal, excessive, or synchronous neuronal activity in the brain 1, 3
• Seizures can be provoked (acute symptomatic) occurring during systemic illness or brain insult, or unprovoked occurring without precipitating factors 4
• Approximately 10% of the population will experience at least one seizure during their lifetime, but this does not mean they have epilepsy 1, 5
• A single unprovoked seizure has an incidence of 23-61 per 100,000 person-years 4

Epilepsy: The Chronic Disease

• Epilepsy is diagnosed when any of three criteria are met: 1, 2

  • At least two unprovoked seizures occurring more than 24 hours apart
  • One unprovoked seizure with probability of recurrence similar to the general recurrence risk after two unprovoked seizures (≥60%)
  • Diagnosis of a specific epilepsy syndrome

• Epilepsy is not a single disease but a heterogeneous group of disorders characterized by recurrent, usually unprovoked seizures 6

• Active epilepsy affects approximately 1.2% of the US population (3.4 million people) and 50 million people worldwide 1

Clinical Implications of the Distinction

When to Initiate Treatment

• Provoked (acute symptomatic) seizures are treated by addressing the underlying cause; antiepileptic drugs are not indicated 5
• A single unprovoked seizure may warrant antiepileptic drug therapy if high-risk features are present: history of brain insult, epileptiform abnormalities on EEG, or structural lesion on neuroimaging 5, 3
• Epilepsy (recurrent unprovoked seizures) requires antiepileptic drug therapy as standard treatment 5

Prognostic Differences

• A single unprovoked seizure carries a standardized mortality ratio (SMR) of 2.3 4
• Newly diagnosed epilepsy (unprovoked seizures) has an SMR ranging from 2.5 to 4.1, highest in young patients and those with symptomatic seizures 4
• Persistent seizures in epilepsy are associated with 20-40% risk of bodily injuries (fractures, burns, concussions) over 12-month follow-up 3

Diagnostic Approach to Classification

Essential Distinguishing Features

• Correct identification of seizure type (focal onset, generalized onset, or unknown onset) is crucial before determining if epilepsy is present 1, 7
• Epilepsy syndrome classification requires multiple factors beyond just seizure recurrence: age at onset, seizure types, intellectual development, neurologic examination findings, EEG patterns, and neuroimaging results 6, 5
• Understanding the epilepsy syndrome provides powerful prognostic and treatment guidance that extends beyond simply counting seizure episodes 6

Key Diagnostic Pitfall

• Do not confuse seizure frequency with epilepsy diagnosis—a patient having multiple seizures in a 24-hour period (such as in status epilepticus or during acute illness) does not automatically meet epilepsy criteria if these are provoked seizures 4
• When uncertain about epilepsy diagnosis, it is better to postpone the diagnosis than to falsely diagnose it, as this has significant treatment and psychosocial implications 8