Focal Bilateral Tonic Clonic Seizures (Secondarily Generalized Seizures)


These seizures are called focal to bilateral tonic-clonic, because they start in a limited area on one side of the brain and spread to involve both sides. This is different from a generalized onset tonic-clonic seizure, which starts on both sides of the brain.

Focal onset seizures have an abnormal region of brain leading to the electrical storm of a seizure. The place and cause of focal onset may not be detectable by testing. Generalized onset seizures are believed to result from neurochemical and genetic abnormalities widespread throughout brain, and no focal injured brain region is involved.

  • Bilateral tonic-clonic seizures happen in more than 3 out of 10 people with focal epilepsy.
  • Sometimes the person does not recall the beginning of the seizure or the seizure spreads quickly so the first part is hard to see. This part usually lasts seconds to less than a minute.
  • The bilateral tonic-clonic part of these seizures usually lasts less than 2 or 3 minutes.

They can happen in people of any age who have focal onset seizures.

  • These seizures may look dramatic. They start suddenly and the movements can be strong or forceful.
  • The seizure may begin with an aura or focal onset aware seizure (previously called simple partial seizure). For example, the seizure may start with a smell, feeling of nausea, or change in sensation or movement. The eyes or head may turn forcefully to one side. The person is fully aware of what’s happening at this point.
  • This seizure type can also begin with a focal onset impaired awareness seizure (previously called complex partial seizure). The person may be confused or not aware of what happens during the seizure.
  • The bilateral tonic-clonic part usually begins with stiffening of the muscles (called the tonic phase).
    • Air being forced past the vocal cords causes a cry or groan. The sound probably does not reflect pain or distress, because the person is not aware at this point.
    • The person loses consciousness and falls to the floor.
    • The tongue or cheek may be bitten, so bloody saliva may come from the mouth.
    • Breathing can be temporarily impaired, and the person may look blue in the face.
  • Jerking movements happen next (called the clonic phase).
    • The arms, legs, and face begin to jerk quickly and repeatedly; bending and relaxing at the elbows, hips, and knees can be seen.
    • After a few minutes, the jerking slows and stops.
  • A person may lose control of their bladder or bowel as the body relaxes.
  • Consciousness returns slowly. The person may be drowsy, confused, agitated, or depressed after the seizure, for hours or sometimes for days.
  • The active part of the seizure generally lasts 1 to 3 minutes. It can take much longer (minutes to hours) for some people to fully recover after it.
  • A tonic-clonic seizure that lasts longer than 5 minutes is a medical emergency.
  • It may be hard to tell if a tonic-clonic seizure starts as focal or generalized onset, especially if they occur during sleep or are not seen by anyone else. Then they are called unknown onset tonic-clonic seizures.
  • Most tonic-clonic seizures during sleep begin in one area and have a focal onset.
  • After the seizure, consciousness returns slowly, and the person may be drowsy, confused, agitated, or depressed for a while. Some people may need to rest for a few hours after a seizure, while others return to their normal state within minutes.
  • If the person does not return to normal, or if another seizure occurs before they return to normal, this may be a sign of a seizure emergency called status epilepticus.

It depends and varies among people and the type of epilepsy syndrome they have. Some people can have seizures daily, several times a week, several times a month, or occasionally throughout the year. Some people only have one in their lifetime. Others may be able to control these seizures completely with seizure medication.

EEG (electroencephalogram) and MRI (magnetic resonance imaging) scans may help sort out where the seizure starts: in one area (focal onset) or on both sides of the brain (generalized onset).

  • Many convulsive seizures can be controlled with medication.
  • If a person has convulsive seizures that are not well controlled with medication, testing may be needed to see whether they might be focal to bilateral tonic-clonic seizures that begin in a limited area of the brain.
  • If they do begin in one area, surgery or neurostimulation could be an option for treatment.
  • Devices and diet therapy are also used to treat focal to bilateral tonic-clonic seizures (previously known as secondarily generalized seizures).

If you think your loved one or yourself may be having focal to bilateral tonic-clonic seizures, it is important to let your doctor know your concerns right away. Uncontrolled seizures may lead to injury, memory impairment, and in some rare cases death. Getting a diagnosis and treatment is of utmost urgency.

Authored By:

Elaine Kiriakopoulos MD, MSc

Reviewed By:

Robert Fisher MD, PhD


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