Febrile Seizures

Febrile seizures are common in children between the ages of three months and five years. They happen when a child has a fever and are considered provoked seizures, rather than a true epilepsy syndrome. They are frightening, but usually do not cause harm, and go away on their own when the child is older.

What are other terms for febrile seizures?

Other terms for febrile seizures that you may come across include:

• febrile convulsions
• febrile fits
• fever convulsions
• fever seizure
• pyrexial seizures

What causes febrile seizures?

Three things interact to put young children at risk for febrile seizures:

• a child’s developing brain
• a genetic predisposition to seizures
• fever

Because febrile seizures occur during a specific age range, we know that the stage of a child’s brain development is an important factor.

There is a strong genetic component to febrile seizures. The parents of children with febrile seizures often had febrile seizures as well, and the risk that a child’s brother or sister will also have febrile seizures is about 25%. Although the specific genes involved have not been identified in most cases, researchers have associated several different chromosomes with febrile seizures, including chromosomes 8, 19, and 2. It is possible that some families have more than one affected gene.

The rare syndrome of generalized epilepsy with febrile seizures plus (see below) is caused by an autosomal dominant mutation that affects the sodium channels of neurons.

Fever may be caused by almost any common childhood illness or infection, including:

• upper respiratory infection (colds or flu)
• ear infection
• pneumonia
• gastroenteritis (“stomach flu”)
• roseola

Note that if a seizure is provoked by a CNS infection such as meningitis, it is not considered a febrile seizure.

Risk factors for a first febrile seizure include:

• a relative with febrile seizures
• delayed discharge from hospital after birth (more than 28 days)
• delayed development
• attending day care, probably due to more frequent illnesses with fever

If a child has two or more of these risk factors, she has about a 30% chance of having a first febrile seizure.

What are the features of febrile seizures?

Most febrile seizures happen between the ages of six months and three years, although they can occur in younger or older children.  There are two types of febrile seizures:

• Simple febrile seizures are generalized tonic-clonic seizures that last for less than 15 minutes. The child does not have another seizure for at least 24 hours, if at all. At least 75% of febrile seizures are simple.
• Febrile seizures are considered complex if they are partial seizures, if they last for more than 15 minutes, if there are clusters of two or more seizures within 24 hours, or if they occur in a child with a developmental disability.

Febrile seizures usually happen quite early in the course of the illness. Sometimes the seizure happens even before a parent knows that the child is ill or has a fever.

Febrile status epilepticus is fairly common, and can be the first sign of chronic epilepsy. However, the risk of epilepsy, brain damage, or death as a result is low.

Generalized epilepsies with febrile seizures plus

This is a group of several syndromes which has recently been described in the medical literature. In these syndromes, multiple members of a family may have different types of seizures. In most cases, some family members have febrile seizures, which may persist beyond the age when they would normally grow out of them. Other members of the family may have generalized tonic-clonic, myoclonic, or absence seizures. This condition has been associated with several different genetic mutations. They appear to be inherited in an autosomal dominant fashion. Only a small fraction of febrile seizures are caused by these syndromes.

How many other children have febrile seizures?

Febrile seizures are common. Between 3% and 4% of children have had one or more febrile seizures by age seven. They are slightly more common in boys than in girls.

How do you know that a child has febrile seizures?

To diagnose a febrile seizure, the doctor will ask the child’s parent or whoever observed the seizure to describe it carefully. He will conduct a physical and neurological examination. If the cause of the fever is known, and the child is not confused or unconscious, he will not usually ask for any laboratory tests. However, if he suspects something else is wrong, he may order some blood tests.

It is important to rule out other possible causes of seizures, such as a CNS infection. In babies who are less than a year old, or older children who have been treated with antibiotics, the symptoms of meningitis may not be obvious and the doctor may order a lumbar puncture to rule this out.

Unless the doctor suspects that the seizures have some other cause besides the fever, he will probably not order an EEG or imaging tests such as an MRI or CT scan.

How are febrile seizures treated?

A child having a febrile seizure should be given normal first aid. If the seizure lasts longer than five minutes, she should be taken to an emergency department. It is rarely necessary to admit a child with a first, simple febrile seizure to hospital.

If the child has a fever, it may be helpful to give her an anti-fever medication such as acetaminophen to keep the fever down and make her more comfortable, although one study has found that this does not prevent seizures.

Diazepam may be prescribed to prevent or shorten seizures in a child with fever. However, this is rarely prescribed because the medication can cause drowsiness and may mask the signs of serious infection.

It is usually not necessary to give anti-epileptic drugs to a child who has febrile seizures, since the potential side effects probably outweigh the possible benefits. There is no evidence that giving anti-epileptic drugs will prevent the child from developing epilepsy later on.

What is the outlook for a child with febrile seizures?

One researcher has noted that the only serious long-term effect of febrile seizures is parental anxiety. In fact, the outlook for a child with febrile seizures is good. Most children with one febrile seizure never have another, and very few children with febrile seizures go on to develop epilepsy.

Between 30% and 40% of children who have had one febrile seizure will have at least one more, usually within a year of the first one. A child is more likely to have another febrile seizure if:

• she is less than a year old
• she has a family history of febrile seizures
• she had a seizure soon after her fever began
• her temperature was not very high when she had the seizure

Between 1.5% and 4.6% of children with any type of febrile seizure will later develop epilepsy. The risk factors for developing epilepsy include:

• neurological or developmental problems before the first seizure
• family history of non-febrile seizures
• complex febrile seizures

Children with two or more of these risk factors have a 10% chance of developing epilepsy. Children with none of these risk factors have about the same risk of developing epilepsy as children without febrile seizures.

About 15% of children with epilepsy have a history of febrile seizures. They are particularly common in children who later develop mesial temporal sclerosis. Mesial temporal sclerosis is a condition in which neurons in part of the temporal lobe die; it is linked to temporal lobe epilepsy. However, there is no evidence that uncomplicated febrile seizures cause epilepsy. Rather, children with febrile seizures may have some underlying genetic predisposition to seizures and epilepsy.

There is no evidence that a short febrile seizure damages the brain. Studies of children with febrile seizures and their siblings without febrile seizures showed no difference in intelligence, school achievement, behaviour, height, or head circumference.