Uncontrolled electrical activity in the brain, which may produce a physical convulsion, minor physical signs, thought disturbances, or a combination of symptoms. The type of symptoms and seizures depend on where the abnormal electrical activity takes place in the brain, what its cause is, and such factors as the patient’s age and general state of health. Seizures can be caused by head injuries, brain tumors, lead poisoning, maldevelopment of the brain, genetic and infectious illnesses, and fevers. In fully half of the patients with seizures, no cause can yet be found.
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1. An attack; the sudden onset of a disease or of certain symptoms. 2. An epileptic attack. SYN: convulsion (2). [O. Fr. seisir, to grasp, fr. Germanic]
- absence s. a s. characterized by impaired awareness of interaction with, or memory of, ongoing events external or internal to the person; may comprise the following elements: mental confusion, diminished awareness of environment, inability to respond to internal or external stimuli, and amnesia. (The term absence was first used by Louis-Florentin Calmeil (1798–1895) to introduce the concept of epileptic absence for the brief loss of consciousness or confusion seen in epileptic patients.)
- akinetic s. SYN: atonic s..
- anosognosic seizures SYN: anosognosic epilepsy.
- astatic s. s. causing loss of erect posture.
- atonic s. a s. characterized by sudden, brief (1–2 s.) loss of muscle tone, involving postural muscles; the term usually applies to bilaterally synchronous events. SYN: akinetic s..
- atypical absence s. an absence s. associated with an EEG pattern of irregular or slow spike and wave at less than 2.5 Hz or paroxysmal fast activity on an abnormally slow background EEG.
- audiogenic s. a reflex s. precipitated by loud noises, rare in humans. Audiogenic seizures in rodents are an animal model of epilepsy.
- automotor s. s. characterized by an automatism predominantly involving the distal limbs.
- autonomic s. s. characterized by objectively documented dysfunction of the autonomic nervous system, usually involving cardiovascular, gastrointestinal, or sudomotor functions.
- clonic s. a s. characterized by repetitive rhythmical jerking of all or part of the body.
- complex motor s. s. characterized by muscles of each limb contracting asynchronously and sequentially to produce a movement that may resemble voluntary activity.
- complex partial s. a s. with impairment of consciousness, occurring in a patient with focal epilepsy.
- convulsive s. s. with clonic or tonic-clonic motor activity.
- dileptic s. s. characterized by impaired awareness of, interaction with, or memory of ongoing events.
- early s. a s. occurring within one week after craniocerebral trauma.
- electrographic s. SYN: subclinical s..
- epileptic s. clinical and/or laboratory manifestations of an epileptic attack.
- febrile s. SYN: febrile convulsion.
- focal motor s. a simple partial s. with localized motor activity.
- gelastic s. a s. characterized by bursts of involuntary laughter or giggling, usually without an appropriate affective tone; most often related to hypothalamic lesions, such as hamartomas.
- generalized seizures seizures characterized by generalized clinical manifestations.
- generalized tonic-clonic s. a generalized s. characterized by the sudden onset of tonic contraction of the muscles often associated with a cry or moan, and frequently resulting in a fall to the ground. The tonic phase of the s. gradually give way to clonic convulsive movements occurring bilaterally and synchronously before slowing and eventually stopping, followed by a variable period of unconsciousness and gradual recovery. SYN: cryptogenic epilepsy, generalized tonic-clonic epilepsy, grand mal s., grand mal, idiopathic epilepsy (2), major epilepsy.
- grand mal s. SYN: generalized tonic-clonic s..
- hypermotor s. s. characterized by automatisms involving predominantly proximal limb muscles and producing marked limb displacement.
- hypomotor s. s. characterized by complete or partial arrest of ongoing motor activity in a patient whose level of consciousness cannot be determined accurately ( e.g., newborns, infants, mentally retarded patients).
- jacksonian s. a motor s. that initially involves one part of the body and then progressively spreads to other parts of the body on the same side; may become generalized; often originates in or near the contralateral rolandic neocortex. SYN: jacksonian epilepsy.
- late s. a s. that occurs greater than one week after a craniocerebral trauma or CNS insult.
- major motor s. a grand mal s. or other convulsive s..
- minor motor s. old term for nonconvulsive s. seen in patients with secondary generalized epilepsies.
- myoclonic s. a s. characterized by sudden, brief (200-ms) contractions of muscle fibers, muscles, or groups of muscles of variable topography (axial, proximal, or distal limb).
- negative myoclonic s. s. characterized by abrupt, brief cessation of muscular activity, occasionally preceded by a single myoclonic contraction; term usually is applied to unilateral, distal muscles.
- nonconvulsive s. a s. without clonic or tonic activity or other convulsive motor activity. SEE ALSO: complex partial s., absence s..
- nonepileptic s. any behavior that resembles a s., but is not epileptic, i.e., not associated with abnormal cerebral EEG activity. SEE ALSO: psychogenic s..
- partial s. s. characterized by localized cerebral ictal onset. The symptoms experienced are dependent on the cortical area of ictal onset or s. spread.
- petit mal s. obsolescent term for a cerebral s. not manifested by tonic-clonic movements ( i.e., grand mal); formerly thought to be the clinical manifestation solely of a 3-s. spike in wave pattern, as seen on electroencephalography, but now known to be associated with several different EEG patterns.
- psychic s. a simple partial s. characterized by an attack of psychic phenomena such as a dreamy state, déjà vu, autonomic sensation or emotion; commonly, but not exclusively, associated with temporal lobe epilepsy.
- psychogenic s. a clinical spell that resembles an epileptic s., but is not due to epilepsy. The EEG is normal during an attack, and the behavior is often related to psychiatric disturbance, such as a conversion disorder.
- psychomotor s. a s. characterized by psychic manifestation, and a complex motor s.. See psychic s..
- secondarily generalized tonic-clonic s. a generalized tonic-clonic s. that begins with a partial s. and evolves into a generalized tonic-clonic s..
- simple partial s. a partial s. that is not associated with impairment of consciousness; seen in patients with focal epilepsy.
- subclinical s. a s. detected by EEG, which has no clinical correlate, i.e., an EEG s. alone. SYN: electrographic s..
- tonic s. a s. characterized by a sustained increase in muscle tone, of abrupt or gradual onset and offset, lasting a few seconds to a minute, usually 10–20 s.; tonic seizures affecting proximal muscles bilaterally frequently lead to the adoption of a posture.
- tonic-clonic s. a s. characterized by a sequence consisting of a tonic-clonic phase; when generalized, constitutes what has been known as a “grand mal” s..
- versive s. a s. characterized by sustained, forced conjugate ocular and cephalic and/or truncal deviation.

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sei·zure 'sē-zhər n
1) a sudden attack (as of disease) esp the physical manifestations (as convulsions, sensory disturbances, or loss of consciousness) resulting from abnormal electrical discharges in the brain (as in epilepsy)
2) an abnormal electrical discharge in the brain

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sei·zure (seґzhər) 1. the sudden attack or recurrence of a disease. 2. a single episode of epilepsy; often a seizure is named for the kind of epilepsy it represents (see under epilepsy). Called also convulsion.

Medical dictionary. 2011.

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