What is a Clonic Seizure?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 30 October 2018
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A clonic seizure is a type of seizure where the muscles repeatedly contract and release, causing the patient to jerk uncontrollably. There are a variety of causes for clonic seizures, ranging from seizure disorders like epilepsy to medication overdoses. Supportive therapy can be provided during a seizure to reduce the risk of injury and further medical evaluation may be recommended in some situations.

With a clonic seizure, the patient's arms and legs will jerk, sometimes on both sides of the body and sometimes just on one side. During a seizure, providing support for the head without holding the head or trying to hold the patient down is helpful. A towel or pillow under the head can reduce the risk of injury for the patient. When the seizure is over, the patient can be rolled onto her or his side to ensure that the airway is clear. Because people are sometimes confused or upset after a seizure, remaining calm, speaking in a low voice, and letting the person know what has happened is beneficial.

In some people, repeat clonic seizures can lead eventually to tonic-clonic seizures, also known as grand mal seizures. In these cases, patients will first stiffen and then jerk during an attack. This is the type of seizure many people associate with epilepsy, but it is relatively rare and not all people with epilepsy will develop grand mal seizures. In other instances, the seizure is a one time event.


If there is a known cause for a clonic seizure and a patient is already in treatment for it, additional evaluation after the seizure may not be needed unless the patient appears to be experiencing neurological deficits. If someone spontaneously has a seizure with no history to explain why, it can be advisable to consult a neurologist for an evaluation. The doctor can request an electroencephalogram to review brain activity, conduct an examination, and interview the patient to identify potential causes for the seizure.

While a clonic seizure is not a medical emergency as long as the patient is supported during the seizure and appears to be recovering well, there is a condition called status epilecticus that does require immediate medical attention. In status epilepticus, the brain persists in seizing, essentially caught in a loop. If a clonic seizure continues for more than five minutes, the patient may be experiencing status epilepticus and emergency services should be called immediately.



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