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Seizures
Seizures & Epilepsy
Key Definitions
Seizure
A seizure is an acute, transient neurological event (typically less than 5 minutes in duration) caused¬ by abnormal (excessive or synchronous) electrical discharges within the brain.
Epilepsy
Epilepsy is a syndrome of recurrent, unprovoked seizures. Provoked seizures can occur from conditions like intracranial hemorrhage or metabolic causes; unprovoked seizures do not have a triggering cause.
Status Epilepticus
Status epilepticus refers to seizure activity that fails to terminate within the anticipated time period (variably defined as anywhere from 5 – 30 minutes) OR it refers to a series of consecutive seizures without intervening recovery.
Status epilepticus has a mortality of 15 – 20%; however, it is the underlying etiology for the seizures that is the major contributor to this poor prognosis. Thus, as clinicians, we should never "give-up" on a patient no matter how long the duration of the status epilepticus, as the seizures can persist for weeks and patients can still have a good outcome if the underlying etiology resolves or is treated. For more information on the management of status epilepticus, see the lecture primer Seizure Evaluation & Managment.
Key Epidemiology
Seizure Prevalence
- 5 to 10% of people will have a seizure at some point in their life; most often in early childhood or late adulthood.
Epilepsy Prevalence
- 1 to 4% of people have epilepsy; different organizations and societies provide widely varying estimates.
- The World Health Organization (WHO) and Centers for Disease Control (CDC) an epilepsy prevalence of ~ 1% whereas the American Epilepsy Society reports a figure of ~ 4%.
Common Causes of Provoked Seizures
- Stroke
- Brain tumor
- Brain injury
- CNS infection
Most Common Cause of Epilepsy, Worldwide
- Neurocysticercosis (taenia solium) is the most common cause of epilepsy, worldwide.
Seizure Categorization
Onset Pattern
Focal (aka Partial)
- Focal (aka partial) onset seizures originate from networks within one hemisphere (typically in a discrete region).
Generalized
- Generalized onset seizures originate from networks that involve both hemispheres.
Focal to Generalized (aka Secondarily Generalized)
- If a seizure begins in one hemisphere and subsequently involves both hemispheres, we call this a focal to bilateral seizure (aka secondarily generalized seizure).
Focal
- In focal onset seizures, awareness (ie, consciousness) can be impaired (aka complex partial seizures) or preserved (aka simple partial seizures).
- Note, that in generalized seizures, by definition, awareness is almost always impaired.
- Clinically, focal seizures can have either motor or non-motor features.
Generalized
- Motor & Non-Motor seizures.
- Major types of motor seizures:
- Tonic-clonic
- Myoclonic
- Atonic
- Major non-motor seizure type:
- Absence
Generalized Seizures
Tonic-Clonic
- Most prominent generalized, motor seizure
Semiology
- Tonic phase = stiffening; Clonic phase = rhythmic jerking.
Mimicker
- A key mimicker of tonic-clonic seizure is convulsive syncope, which are convulsions brought on by syncope, a loss of adequate cerebral perfusion, rather than by abnormal electrical activity in the brain.
- Bear in mind that one of the most common mimickers of generalized seizures, and most seizure types, is actually non-epileptic spells (aka psychogenic seizures).
Syndromes
- Generalized tonic-clonic seizures can occur in a wide-variety of epilepsy syndromes.
Nomenclature
2017 ILAE (International League Against Epilepsy) classification system
Seizure Description
Although the following terms are still widely used, the 2017 ILAE classification system has made the following updates:
- Partial seizures are now referred to as focal seizures
- Complex partial seizures are now referred to as focal onset that resulted in loss of awareness.
- Simple partial seizures are now referred to as focal seizures with NO loss of awareness.
- Secondarily generalized seizures are now referred to as seizures of focal onset that ultimately generalized; these are now called focal to bilateral tonic-clonic seizures.