Bilateral Tonic-Clonic Seizures

By: Natalie L. Boehm, MBA, RBLP-T

What are seizures? What is epilepsy?

According to the International League Against Epilepsy (ILAE) and the International Bureau for Epilepsy (IBE), an epileptic seizure is defined as a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain. The two organizations define epilepsy as a disorder of the brain characterized by an enduring predisposition to generate epileptic seizures and by the neurobiologic, cognitive, psychological, and social consequences of this condition.

According to the ILAE and IBE to be diagnosed with epilepsy, the patient must have at least one epileptic seizures. The Center for Disease Control (CDC) states doctors diagnose epilepsy when the patient has had two or more seizures. Depending on the type of seizure the patient is having, diagnosing epilepsy can be very difficult.

What is a bilateral tonic-clonic seizure?

Bilateral tonic-clonic seizures affect both sides of the brain but does not start on both sides of the brain. The person experiences a focal seizure in one area of the brain and then the seizure spreads to other areas of the brain, turning into a tonic-clonic seizure.

Bilateral tonic-clonic vs. Generalized tonic-clonic

Bilateral tonic-clonic and generalized tonic-clonic seizures start differently in the brain and are caused by different events. Bilateral tonic-clonic seizures start as a focal seizure, located in one area of the brain. The person is aware of their surroundings at that point. The activity then crosses over to the other hemisphere of the brain, becoming a tonic-clonic. Traumatic brain injuries, brain tumors, stroke, infections, and aneurysms are a few examples of what can cause someone to have bilateral tonic-clonic seizures.

Generalized tonic-clonic seizures begin on both sides of the brain. Generalized tonic-clonic seizures are caused by genetic abnormalities and are associated with certain epilepsy syndromes.

Seizure first aid for bilateral tonic-clonic seizures

If someone has a bilateral tonic-clonic seizure remember to stay calm. They will at first show signs of a focal seizure. Symptoms may be feelings of déjà vu, strange smells or taste, extreme fear or happiness, or numbing/tingling in areas of the body. When the seizure activity spreads to the other hemisphere of the brain, that is when a tonic-clonic seizure will begin. The person will lose consciousness. If someone has a tonic-clonic seizure, please do the following:

  • First stay calm.
  • Start timing the seizure and turn the person on their side.
  • Do not put anything in their mouth.
  • Make sure the area is clear of things that could result in them sustaining injury.
  • Place a folded blanket or folded piece of clothing under their head to avoid injury.
  • If the seizure lasts for more than five minutes or repeats, call for medical help.

Treatment for bilateral tonic-clonic seizures

Anticonvulsant medication is the first source that is used to treat bilateral tonic-clonic seizures. Some people may be prescribed rescue medication to prevent the seizures from being prolonged or the person going into status epilepticus.

When medication is not enough or people are drug-resistant, options such as the keto diet can help to reduce seizure activity. A vagus nerve stimulator (VNS) or a responsive neurostimulator (RNS) is another option.


Bilateral tonic-clonic seizures start off as focal seizures and then progress to tonic-clonic seizures. It is important to recognize the signs and symptoms of a seizure and know how to administer first aid when needed.


Center for Disease Control (2020). Epilepsy: Types of Seizures. Retrieved from:

Fisher, B. (2005). Epileptic Seizures and Epilepsy: Definitions Proposed by the International League Against Epilepsy (ILAE) and the International Bureau for Epilepsy (IBE). Epilepsia. (Copenhagen), 46(4), 470-472.

International League Against Epilepsy (2020). Focal to Bilateral Tonic-Clonic Seizure. International League Against Epilepsy. Retrieved from:

John Hopkins Medicine (2020). Tonic-Clonic (Grand Mal) Seizures. John Hopkins Medicine. Retrieved from:

Kiriakopoulos, E. and Osborne Shafer, P. (2017). Focal to Bilateral Tonic-clonic Seizures (secondarily generalized seizures). Epilepsy Foundation. Retrieved from:

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