Generalized seizures are thought to be caused by a nearly simultaneous activation of the entire cerebral cortex, perhaps caused by an electrical discharge originating deep in the brain and spreading outward. The attacks begin with abrupt loss of consciousness. This may be the only clinical manifestation of the seizures (as in absence attacks), or there may be a variety of motor manifestations (myoclonic jerks, tonic posturing, clonic jerking of the body and extremities, etc.).
Generalized tonic-clonic seizures (grand mal) are the most familiar and dramatic of the generalized seizures. They begin with abrupt loss of consciousness; there is usually no warning or aura. In a typical attack, the patient suddenly becomes rigid, trunk and extremities are extended, and the patient falls to the ground. Patients are often apneic during this period and may be deeply cyanotic. They often urinate and may vomit. As the rigid (tonic) phase subsides, there is increasing coarse trembling that evolves into a symmetrical rhythmic (clonic) jerking of the trunk and extremities. As the attack ends, the patient is left flaccid and unconscious, often with deep, rapid breathing. Typical attacks last from 60 to 90 s (occasionally longer). Bystanders generally overestimate the duration of the seizure. Consciousness returns gradually, and postictal confusion and fatigue may persist for several hours or longer.
Absence seizures (petit mal) are very brief, generally lasting only a few seconds. The patients suddenly lose consciousness without losing postural tone. They appear confused, detached, or withdrawn, and current activity ceases. They may stare and have twitching of their eyelids. They do not respond to voice or to other stimulation, exhibit voluntary movements, or lose continence. The attack ceases abruptly, and the patients are able to resume their previous activity with no postictal symptoms. Both the patients and witnesses may be unaware that anything has happened. Classic absence seizures are limited to school-aged children and are often attributed by parents and teachers to daydreaming or not paying attention. The attacks may be very frequent, sometimes occurring 100 or more times daily, and may result in poor school performance. Petit mal attacks may occur alone or in association with other kinds of seizures. They usually resolve as the child matures. Similar attacks in adults are more likely to be minor complex partial seizures and should not be called absence. The distinction is important, because the causes and treatment of the two seizures are quite different.
There are four less-common seizure classifications with which the clinician should be familiar. Myoclonic seizures are characterized by brief, "shock-like" muscular contractions that may be generalized or limited to one or more extremities. Clonic seizures involve repetitive clonic jerks without the tonic element. Tonic seizures have a prolonged, strained, contraction of the body with deviation of the head and eyes. The patient becomes pale, flushed, then cyanotic, and the body may rotate around in position. Atonic seizures are characterized by a sudden loss of postural tone in the head, trunk, and/or limbs, which may be associated with a brief loss of consciousness.
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