Seizures

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 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 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.

• 5 to 10% of people will have a seizure at some point in their life; most often in early childhood or late adulthood.

• 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%.

• Stroke
• Brain tumor
• Brain injury
• CNS infection

• Neurocysticercosis (taenia solium) is the most common cause of epilepsy, worldwide.

For more on seizure epidemiology, see the whiteboard tutorial Causes of Seizures & Epilepsy.

• Focal (aka partial) onset seizures originate from networks within one hemisphere (typically in a discrete region).

• Generalized onset seizures originate from networks that involve both hemispheres.

• If a seizure begins in one hemisphere and subsequently involves both hemispheres, we call this a focal to bilateral seizure (aka secondarily generalized seizure).

• 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.

• Motor & Non-Motor seizures.
• Major types of motor seizures:
• Tonic-clonic
• Myoclonic
• Atonic
• Major non-motor seizure type:
• Absence

• Most prominent generalized, motor seizure

• Tonic phase = stiffening; Clonic phase = rhythmic jerking.

• 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).

• Generalized tonic-clonic seizures can occur in a wide-variety of epilepsy syndromes.

For more on seizure categorization, see Presentation of Seizures & Epilepsy.

• 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.

For more information on this subject, see: Epilepsy Nomenclature