Dravet syndrome is a severe form of epilepsy characterized by prolonged seizures that usually appear in the first year of life. As the disease progresses, different types of seizures start to occur.
Seizures are classified into three major types depending on the part of the brain they affect: focal onset or partial seizures, generalized seizures, and unknown onset seizures. Focal onset seizures start on one side of the brain while generalized seizures affect both sides of the brain simultaneously. In unknown onset seizures, the location in the brain where the seizure starts is not known.
Seizures also may be classified based on their cause such as, for example, febrile seizures, or seizures caused by high temperature, as well as symptoms they cause, myoclonic seizures, clonic seizures, tonic seizures, tonic-clonic seizures, absence seizures, atonic seizures, focal impaired-awareness seizures.
Febrile seizures usually are of generalized seizure. They are a convulsion triggered by a fever that often accompanies childhood illnesses. In children with Dravet syndrome, they usually occur within the first year after birth and often are much more severe than those seen in children with other diseases.
Most febrile seizures are brief and do not usually cause long-term health problems. However, repetitive prolonged febrile seizures increase children’s risk of developing epilepsy and are the first sign that a child may have Dravet syndrome.
Myoclonic seizures are another type of generalized seizure. This type of seizure causes children’s muscles to rapidly contract and relax, resulting in jerky movements. In children with Dravet syndrome and other epilepsy disorders, these jerking movements occur on both sides of the body. These seizures usually do not affect the child’s consciousness, leaving them aware and able to think during the episode. When these seizures are present in children with Dravet syndrome they usually occur by the age of two.
Clonic seizures can be either focal onset or generalized onset in origin. This type of seizure causes jerky movements in which the person’s muscles stiffen and relax. It often is difficult to differentiate a myoclonic seizure from a clonic seizure, but clonic seizures usually involve a more rhythmic jerky movement. This type of seizure most commonly occurs in babies and may last from a few seconds to one minute. These seizures cannot be stopped by restraining the child.
Tonic seizures can be either focal onset or generalized onset in origin. This type of seizure causes a person’s body to become suddenly stiff. They usually occur while the person is sleeping and last less than 60 seconds. A person experiencing a tonic seizure may be fully aware of the episode or their awareness may be slightly impaired. They may feel tired or confused after the event and have a headache. Tonic seizures are very rare in Dravet syndrome.
Tonic-clonic seizures usually are generalized onset, but also can be focal onset. This type of seizure involves a combination of symptoms from tonic and clonic seizures. The tonic phase of the convulsion begins first with the person’s body suddenly becoming stiff, followed by the clonic phase in which the person’s body jerks rhythmically. These seizures typically last one to three minutes. Toward the end of the seizure, the jerky movements slow to a stop and the person’s body relaxes. During this time, the person may lose control of the bladder or bowels. A tonic-clonic seizure lasting more than five minutes requires immediate medical help.
Absence seizures are a type of generalized onset seizure. This type of seizure causes children to have lapses of consciousness where they have no memory of the incident afterward. These seizures are abrupt and last only a few seconds. They are characterized by non-motor symptoms, although brief twitches may be present. A common symptom of this type of seizure is blank staring that is often mistaken for daydreaming. Once diagnosed, absence seizures can be controlled with anti-seizure medications. It is possible for children to outgrow absence seizures and this commonly happens in their teenage years.
Children with Dravet syndrome also can have another type of absence seizure known as atypical absence seizure. These seizures also are a type of generalized onset seizures and usually occur after age two. Unlike regular absence seizures, children experiencing atypical absence seizures may be able to respond to external stimuli.
Atonic seizures can be either focal onset or generalized onset in origin. These seizures also are known as drop attacks because there is a loss of muscle control that results in limp muscles. They usually last for less than 15 seconds. They cause no direct damage, but may result in indirect injuries from falling. Head protection often is recommended for children with this type of seizure.
Focal impaired-awareness seizures
Focal impaired-awareness seizures usually occur after age two and typically last one to two minutes. They originate in one side of the brain. The patient loses consciousness, so the main symptoms are unresponsiveness and confusion. In addition, children may have automatisms such as lip-smacking or fumbling.
Status epilepticus may occur in children with Dravet syndrome. This is when a seizure lasts more than five minutes or when multiple seizures occur close together with no recovery time in-between. There are two types of status epilepticus — convulsive and non-convulsive. Convulsive status epilepticus usually occurs from a prolonged tonic-clonic seizure. This type requires emergency medical treatment because it is life-threatening. Non-convulsive status epilepticus usually occurs from prolonged absence or focal impaired awareness seizures. These seizures are harder to recognize because the symptoms are more subtle.
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