What is the difference between seizures and epilepsy?

Seizures vs. Epilepsy: Understanding the Difference

A seizure is defined as a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain, while epilepsy is defined as having at least two unprovoked seizures occurring more than 24 hours apart, one unprovoked seizure with a high probability of recurrence, or diagnosis of an epilepsy syndrome. 1

Key Definitions

Seizures

• A seizure is a single, temporary event characterized by abnormal excessive or synchronous neuronal activity in the brain 1
• Approximately 10% of the population will experience at least one seizure during their lifetime 1, 2
• Seizures can be classified as:
  • Provoked seizures: Occur at the time of or within 7 days of an acute neurologic, systemic, metabolic, or toxic insult (e.g., electrolyte abnormalities, withdrawal, toxic ingestions) 1
  • Unprovoked seizures: Occur without acute precipitating factors, including remote symptomatic seizures (resulting from a CNS or systemic insult that occurred more than 7 days in the past) 1

Epilepsy

• Epilepsy is defined by the International League Against Epilepsy (ILAE) as:
  1. At least two unprovoked seizures occurring more than 24 hours apart, OR
  2. One unprovoked seizure and a probability of further seizures similar to the general recurrence risk after two unprovoked seizures (over the next 10 years), OR
  3. Diagnosis of an epilepsy syndrome 1
• Active epilepsy affects approximately 1.2% of the US population (3.4 million people) and 50 million people worldwide 1
• Epilepsy is a chronic neurologic disorder in which spontaneous recurrence of unprovoked seizures is the main symptom 2

Classification of Seizures

• The ILAE classification of seizures was last revised in 2017 1
• Seizures are classified as:
  • Focal onset: Arising within networks of a single cerebral hemisphere; may remain localized or become more widely distributed 1
    • Can be further characterized by motor onset or nonmotor onset symptoms
    • Can be characterized by aware or impaired awareness
  • Generalized onset: Rapidly affect both hemispheres and both sides of the body 1
    • Further subdivided into tonic-clonic, other motor, or nonmotor (absence)
  • Unknown onset: When the origin cannot be determined 1

Clinical Implications

• Correct identification of seizure type and epilepsy syndrome is crucial for:
  • Etiologic diagnosis
  • Appropriate treatment selection
  • Accurate prognostication 1
• Certain types of seizure disorders are associated with structural brain lesions, including tumors, infection, infarction, traumatic brain injury, vascular malformations, and developmental abnormalities 1
• Epilepsy has significant impact on mortality, morbidity, and quality of life, affecting approximately 65 million people worldwide 3

Diagnostic Approach

• Diagnosis often depends on careful history, supported by electroencephalogram (EEG) and neuroimaging 3
• Neuroimaging plays a critical role in identifying structural causes:
  • CT is useful in emergent situations to identify structural pathology requiring immediate intervention 1
  • MRI is more sensitive for detecting subtle abnormalities, especially in orbitofrontal and medial temporal regions 1

Treatment Considerations

• Provoked seizures are treated by addressing the underlying cause; antiepileptic drugs (AEDs) are not typically indicated 2
• For epilepsy, first-line treatment includes medical management with AEDs selected based on seizure type, patient comorbidities, and side effect profiles 3
• Drug-resistant epilepsy may require referral to an epilepsy specialist for consideration of additional medications, epilepsy surgery, neurostimulation, or dietary therapy 3

Common Pitfalls and Caveats

• Many conditions can mimic seizures, including pseudoseizures, syncope, migraine, cerebrovascular disease, movement disorders, and sleep disorders 2
• Not all epileptic seizures indicate epilepsy; many represent a natural response of the normal brain to transient insults (reactive seizures) 4
• Failure to distinguish between a single seizure and epilepsy can lead to unnecessary long-term medication use 2, 4
• Genetic factors can influence both seizures and epilepsy, with certain genetic syndromes having high rates of both epilepsy and other neurological conditions 1