A seizure is a sudden, erratic increase of abnormal electrical activity in the brain that temporarily affects actions and/or cognition and perception. Seizures can last for a few seconds as in absence seizures (formerly called “petit mal” seizures) or up to a few minutes as seen in complex-partial seizures. Symptoms can be as mild as a momentary blank facial expression caused by impaired consciousness in absence seizures, or as severe as the violent convulsions of tonic-clonic seizures (formerly called “grand mal” seizures). In some cases, seizures can be life threatening. A condition in which seizures last longer than five minutes or when one seizure immediately follows another is called status epilepticus. This can cause significant brain damage and death if not promptly treated. A seizure is not a disorder itself, but rather a symptom indicating an underlying central nervous system (CNS) disturbance. Individual symptoms and prognosis vary depending on the type of seizure and causative agent.
While most seizures occur as part of an epileptic disorder, sometimes they can be isolated events. Seemingly unrelated conditions like a high fever (febrile seizures) can lead to seizures, particularly in young children. A stroke can cause single-incident seizures in adults as well. Approximately 5 percent of the population has experienced a single-incident seizure, whereas only 1—2 percent of the population has epileptic seizures. The risk of developing recurrent epileptic seizures can increase after an individual has a single-incident seizure. There are many different types of epilepsy, and they can come from genetic, structural-metabolic, or unknown sources.
Subtypes and Symptoms
The wide variation not only in seizures, but also in etiology has led to the opinion that “epilepsy” is more accurately termed “the epilepsies.” The International League against Epilepsy (ILAE) is currently responsible for the governing of terminology and classification relating to the different types of seizures and epilepsies.
Depending on the subtype of epilepsy, seizure symptoms can vary from visible muscle contractions to sensory and psychic symptoms only perceived by the person experiencing the seizure. Focal seizures were formerly called partial seizures, and though this terminology is now outdated it is useful in describing the symptoms. Motor symptoms in simple partial seizures cause visible muscle twitches. Sequential involvement of muscle groups is called a “march” and is identified as Jackson Ian seizures. Sensory symptoms are usually not noticeable to a bystander, but can cause considerable distress to the patient. These include both somatosensory and special sensory disturbances. Tingling, visual, auditory, olfactory, and gustatory hallucinations may ensue. The sensory aspect of the partial seizures preceding the generalized tonic-clonic seizure is called an “aura.” People with this type of epilepsy often come to recognize an aura as an indicator before the start of a seizure. Psychic symptoms include senses of déjà vu and jamais vu (failure to recognize familiar scenes, people, or words). When the autonomic nervous system is involved, changes in blood pressure and heart rate have been observed along with diaphoresis and pupil dilation.
Absence seizures are a subtype of epilepsy and are typically only seen in children. Victims of this type of epilepsy will either outgrow the seizures or the seizures will progressively worsen. Symptoms present as almost unnoticeable blank stares or unresponsiveness, but can also include some autonomic and mild clonic symptoms. Increased disturbances in muscle tone and more gradual onset are atypical traits of this type of seizure.
Atonic seizures are characterized by momentary loss of muscle tone, whereas myoclonic seizures are brief involuntary muscle contractions. Tonic seizures are rigid contraction of muscles, particularly those of the limbs. Major muscle groups repeatedly contract and relax during clonic seizures. The notorious tonic-clonic seizures involve nearly immediate loss of consciousness followed by both tonic and clonic symptoms.
Complex-partial seizures originating in or involving the mesial temporal limbic structures are the most common type of seizures, and the most common cause is temporal lobe epilepsy (TLE). These seizures will frequently evolve into secondarily generalized seizures. Most patients with TLE have had some prior brain injury such as trauma to the head from riding a bicycle or a car accident, febrile convulsions, or status epilepticus. TLE is usually a permanent condition with variable seizure frequencies within a population of afflicted individuals.
Erin Slocum and Jennifer L. Hellier
See also: Limbic System; Somatosensory Cortex; Somatosensory System
Eadie, M. J. (1994). The understanding of epilepsy across three millennia. Clinical & Experimental Neurology, 31, 1—12.
Fisher, Robert S., & Maslah Saul. (2012). Genetic causes of epilepsy. Stanford School of Medicine. Retrieved from http://neurology.stanford.edu/epilepsy/patientcare/videos/e_09.html
International League against Epilepsy. (2012). Resource Center. Retrieved from http://www.ilae.org/Visitors/Centre/ctf/documents/ILAEHandoutV10_000.pdf