Dravet syndrome is a severe type of inherited epilepsy that begins in infancy. Patients generally start experiencing seizures accompanied by a high fever in the first year of life.

One of the most common types of seizures seen in Dravet syndrome is what are called tonic-clonic seizures. Although more rare, tonic seizures are also known to occur in these patients.

What are tonic seizures?

Tonic seizures are seizures that cause “increased muscle tone,” or the sudden stiffening of muscles. Muscle tone is defined as the level of tension in the muscles, with a residual level always present to maintain posture. When parts of the brain are overstimulated because of a tonic seizure, muscle tone suddenly increases. This pulls muscles taut and causes them to stiffen.

Tonic seizures are usually generalized, starting in both sides of the brain simultaneously. They can also originate on only one side of the brain, being known as focal tonic seizures.

Generalized tonic seizures may affect both sides of the body, or the entire body, from the onset. Focal tonic seizures initially cause seizure symptoms in one area, and may either remain localized in that area or spread elsewhere.

What happens in a tonic seizure?

Tonic seizures are generally short, lasting no longer than a minute and typically less than 20 seconds. During a tonic seizure, different muscle groups may stiffen and the patient generally loses consciousness. Tonic seizures are not associated with convulsions or jerking movements.

Depending on what muscles are affected, the patient’s back may arch, their legs may stretch or contract, their arms may raise, their neck may extend, and their eyes may open and roll upwards. The person may make involuntary noises, or have trouble breathing as chest muscles tighten.

If the seizure is generalized, all of these symptoms may occur simultaneously; if it is focal, only a few of them may be present.

The seizure’s outcome can depends on what the person was doing when it began, and what muscles are affected. Preventing injury is key. For example, a person who was standing at seizure onset may fall — heavily — to the ground if leg muscles stiffen.

If a tonic seizure is prolonged, the patient’s skin may begin to turn blue due to a lack of oxygen (a tightening in chest muscles can breathing difficult). Immediate medical help should be sought in prolonged tonic seizures.

Once the seizure has ended, affected muscles should relax and the patient regain consciousness. He or she may be sleepy or confused.

Tonic seizure management

Tonic seizures can be managed with anticonvulsant medications, or lifestyle modifications if there are known triggers.

Falls have the potential to cause serious injury. If falls from tonic seizures are frequent, it may be wise to a have the person wear a helmet to protect the head.

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