Individuals may experience just one type, or a combination of many; this can depend on which part (and how much) of the brain is affected by the kind of electrical disturbance that produces seizures. The two main categories of seizures include generalized (tonic-clonic, myoclonic, atonic, and absence), and partial (simple and complex).
Generalized seizures indicate that both cerebral hemispheres (sides of the brain) are affected at the start of the seizure. This can result in loss of consciousness (either briefly or for several minutes), and is sub-categorized into several major types: generalized tonic clonic; myoclonic; absence; and atonic.
Generalized Tonic Clonic Seizures
Tonic clonic seizures (formerly known as “grand mal” seizures) are the most common, and usually begin with a stiffening of the limbs (the tonic phase), followed by a jerking of the limbs and contortion of the facial muscles (the clonic phase).
Myoclonic seizures are rapid, brief contractions of bodily muscles which usually occur at the same time on both sides of the body, usually involving a single arm or foot. Most people think of these seizures as a surprising and sudden jerk, or a feeling of momentary “clumsiness”. A variant of that experience (common among people who do not have epilepsy) is the sudden jerk of a foot during the first stages of sleep.
Atonic (“drop attack”) seizures produce an abrupt loss of muscle control. They result in head dropping, loss of upright posture, or even a sudden bodily collapse. Because they are so abrupt, people who experience them can fall with surprising force. Obviously, this can result in severe injuries to the head and face (protective headgear is often used by children and adults to prevent sudden injury). At this time, atonic seizures seem resistant to drug therapy.
Absence seizures (formerly known as “petite mal” seizures) manifest in what is observed as a prolonged lapse of awareness, sometimes accompanied by “blank” staring that can begin and end quite abruptly–usually lasting no more than a few seconds. There is no warning and no after-effect. More common in children than in adults, absence seizures are frequently so brief that they escape detection, even if the child is experiencing 50 to 100 seizures daily!
In partial seizures, electrical disturbance is limited to a specific area of one cerebral hemisphere (side of the brain). Partial seizures are subdivided into two categories:
Simple Partial Seizures
Consciousness is retained with a Simple Partial Seizure.
Complex Partial Seizures
Consciousness is impaired with a Simple Partial Seizure.
The electrical activity causing simple partial seizures can sometimes spread out to produce a much larger generalized seizure (known as secondarily generalized). Partial seizures are the most common type of seizure experienced by people with epilepsy. Virtually any movement, sensory, or emotional symptom can occur as part of a partial seizure, including complex visual or auditory hallucinations.
Key Things to Remember about Partial Seizures
Although partial seizures affect different physical, emotional, or sensory functions of the brain, they have certain traits in common:
- Their duration isn’t long: most last only a minute or two, although people may be confused and need some time following the seizure to recover.
- They end naturally: excepting rare cases, the brain has its own way of bringing the seizure to an end after a minute or two.
- They can’t be externally stopped while in progress: in an emergency, doctors may use drugs to bring a lengthy (or non-stop) seizure to an end. However, the average person must wait for the seizure to run its course, and other individuals in close proximity should protect the person experiencing the seizure from harm while his or her consciousness is clouded by the circumstance.
- They are not dangerous to others: the movements produced by a seizure are almost always too vague, “disorganized” or personal to threaten the safety of those nearby.