Types of Seizures
The International Classification of Epileptic Seizure identifies seizure types by the site of origin in the brain. The two main categories of seizures include partial seizures and generalized seizures. A partial seizure can evolve to a generalized seizure. There are several subtypes of each. Only the most common are described here.
The site of origin is a localized or discreet area in one hemisphere of the brain. The two most common types of partial seizure are simple partial and complex partial.
Simple Partial—These produce symptoms associated with the area of abnormal neural activity in the brain: motor signs, sensory symptoms, autonomic signs and symptoms (involuntary activity controlled by autonomic nervous system), and psychic symptoms (altered states of consciousness). There is no impairment of consciousness in simple partial seizures.
Complex Partial—Impairment of consciousness, characteristic of complex partial seizures (CPS), results in the inability to respond to or carry out simple commands or to execute willed movement, and a lack of awareness of one's surroundings and events. Automatisms may occur. An automatism is a more or less coordinated, involuntary motor activity (e.g., lip smacking, picking, patting, chewing, swallowing). A simple complex seizure may begin as a simple partial seizure.
At the onset, seizure activity occurs simultaneously in large areas of the brain, often in both hemispheres. Seizures can be convulsive or nonconvulsive. The two most common types are tonic-clonic and absence.
Tonic-clonic (in the past, sometimes referred to as grand mal seizures) —There is loss of consciousness during the seizure. The tonic phase, consisting of increased muscle tone (rigidity), is followed by the clonic phase, which involves jerking of the extremities. Automomic symptoms may also be present.
Absence (in the past, sometimes referred to as petit mal seizures) —This type occurs most often in children, usually beginning between the ages of 5 and 12 years and often stopping spontaneously in the teens. The loss of consciousness is so brief that the child usually does not even change position. Most absence seizures last 10 seconds or less. There is no postictal state, but the person usually lacks awareness of what occurs during the seizure.
Myoclonic—These seizures are so brief that they may go unnoticed. They involve sudden muscle contractions that occur much more rapidly than clonic activity and are often confused with tics. Myoclonic seizures occur at all ages and are associated with epileptic syndromes such as West syndrome and Lennox-Gastaut syndrome.
Syndrome- and Situation-Related Epilepsy
Infants and Children—Epilepsy is one of several symptoms that occur in West syndrome and Lennox-Gastaut syndrome. West syndrome, also called infantile spasm, is a rare disorder of infancy and early childhood. It is characterized by epilepsy, hydrocephalus, congenital anomalies, and mental retardation and usually develops in the first year of life.
Lennox-Gastaut syndrome usually develops between the ages of 1 and 8 years old and is characterized by atonic, absence, and myoclonic seizures. Many of these children are developmentally delayed and have behavioral problems.
Adults—Several medical conditions may precipitate epilepsy in adults, notably drug withdrawal, withdrawal from chronic alcohol abuse, eclampsia (during pregnancy), and local insults (e.g., stroke, head trauma, tumors, scar tissue).