A tonic seizure is a type of seizure that causes sudden tension or stiffness in the muscles of the arms, legs, or trunk. During a tonic seizure, the muscle tone is greatly increased, causing the body, arms, or legs to become suddenly stiff or tense. Tonic seizures usually happen during sleep and usually involve all or most of the brain, affecting both sides of the body. They are short, usually lasting less than 20 seconds. A person may be aware or have only a small change in awareness during a tonic seizure. If a person is standing when a tonic seizure starts, they may fall.

Tonic seizures can start on one side of the brain (partial or focal seizures) or on both sides of the brain simultaneously (generalized). When a tonic seizure starts in one area of the brain, stiffening of a part of the body may begin in one area and stay local. These are called focal tonic seizures. When it starts on both sides of the brain, the whole body or both sides of the body may become stiff or tense from the beginning. These are called generalized tonic seizures.

Tonic seizures are a prominent seizure type in Lennox-Gastaut syndrome (LGS) and other types of epilepsy with mixed seizures. However, they can happen to anyone. Stiffening or other movements can be seen in other neurological problems, especially in children, so it is important to get an EEG to confirm tonic seizures. A written description or video of what happens during the seizure is very important for diagnostic purposes.

If someone near you has a tonic seizure, do not put anything in their mouth, do not restrain them, and make sure the area around them is clear of objects that could injure them. If they fall, roll them on their side so they don’t breathe any saliva or other secretions into their lungs (aspirate), make sure they are breathing okay, and ensure they don’t injure themselves. A seizure that lasts more than 5 minutes (status epilepticus), or th...