Febrile seizures affect children under 6 years who have a temperature of 38° Celsius or more. It is most common between 6 months and 5 years, and especially from 6 months to 3 years. About 2 percent to 5 percent of children experience a febrile convulsion before they are 5 years old.
Seizures can look alarming to parents or caregivers, but most seizures are harmless and do not indicate a long-term medical problem. They are usually caused by a sudden spike in temperature.
If a child with a high temperature has a seizure and there is no clear cause or previous diagnosed neurological or developmental issue, it will be considered a febrile seizure.
Types of febrile seizure
It is not uncommon for young children to experience a seizure when they have a fever.
There are two types of febrile seizure:
- Simple febrile seizures last under 15 minutes and do not happen again during an infection
- Complex febrile seizures may happen several times during an infection, and may last longer than 15 minutes
About 9 in every 10 febrile seizures are simple febrile seizures.
What causes febrile seizures?
Febrile seizures tend to occur because the child's body temperature suddenly rises.
They mostly happen during the first day of the fever, but may occur as the high body temperature is coming down.
Far less common but very serious are infections of the central nervous system that affect the brain and the spinal cord, including encephalitis and meningitis. Seizures linked to these conditions may have a more serious cause.
Do vaccinations cause seizures?
There is a very small risk of a febrile seizure after vaccination. Some studies suggest that 25 to 34 children out of every 100,000 have a febrile seizure after the measles, mumps, and rubella (MMR) vaccine.
The risk is even lower following the antidiphtheria, whooping cough, tetanus, polio, and hemophilus influenza type b vaccine (DTaP/IPV/Hib). The rate is around 6 to 9 cases out of every 100,000 vaccinations.
After a routine vaccination, there is a very small chance of febrile seizure.
A febrile seizure that occurs soon after a vaccination is probably caused by the fever itself, rather than the vaccination.
The vaccination can cause the temperature to rise as the body "ramps up" to fight the intruder. This can lead to a febrile seizure.
After a DTP immunization, the risk is highest on the day of the vaccination when the fever is most likely to rise, but after the MMR vaccination, it may happen between 8 and 14 days later.
Research shows that while there is a small risk of a seizure following a vaccination, any long-term adverse effects are unlikely.
Doctors encourage immunization, and they urge parents to complete the vaccination schedule, even if a child has febrile seizures after a jab. This is because the risks and complications of diseases such as measles are far greater.
How can parents recognize a febrile seizure?
A febrile seizure often happens at the beginning of an illness, as the fever starts, and often before the parents realize the child is sick.
The parents or caregivers may notice the following signs:
- The child's body becomes stiff
- Arms and legs start to twitch, shake or jerk on both sides of the body
- They may have trouble breathing
- They will lose consciousness
- They may lose control of their bladder or their bowels
- They may vomit
- They may foam at the mouth
- Their eyes may roll back in the head
- They may cry or moan.
Most seizures last only a few minutes, but they may cause drowsiness for up to an hour.
Complex febrile seizures may last over 15 minutes, and the child may experience several seizures while they are ill. The child may twitch on only one side of the body, known as a focal seizure.
Even though a fever triggers a febrile seizure, the severity of signs and symptoms are not necessarily linked to the severity of the fever.
How are febrile seizures diagnosed?
Blood and urine tests can detect an infection, and what kind it is. If the child is very young, it may be difficult to get a urine sample. This may have to take place in the hospital.
If the physician suspects an infection in the brain and spinal cord, a spinal tap, or lumbar puncture, may be needed. Using a local anesthetic, the doctor inserts a needle into the child's lower back to remove a small amount of spinal fluid.
This will determine whether there is any infection in the fluid surrounding the brain and spinal cord.
If the child has a complex febrile seizure, further tests may be needed.
What is the treatment for febrile seizures?
A child who has a febrile seizure should be placed in the recovery position, on their side, with their face turned to one side.
This will stop them from swallowing any vomit, it will keep their airways open, and it will help prevent injury.
A caregiver should stay with the child and time the seizure, if possible.
If it lasts less than 5 minutes, the caregiver should call the doctor.
If it lasts longer, they should call for an ambulance. Even though it is probably not serious, it is a sensible precaution.
In rare cases, where the seizure continues until the child arrives at the emergency room, a hospital doctor may give medication to stop the seizure.
If the seizure is particularly long, if the infection appears to be a serious one, or if doctors do not know what is causing it, the child may have to stay in the hospital for observation.
Nobody should put anything into the child's mouth during the seizure.
A person who is having a seizure cannot "swallow their tongue," but putting something in the mouth could be dangerous, potentially breaking a tooth, which could then be inhaled into the lungs.
Treating recurring febrile seizures
About 1 in 3 children will have another seizure within the next 12 months, when they have another infection. This is more likely if:
- The first febrile seizure happened before the age of 18 months
- The first seizure accompanied a low fever
- The child has previously had a complex febrile seizure
- There is a family history of seizures
- There is a family history of epilepsy
- The child attends a day nursery, where more childhood infections are likely.
Complications or lasting effects are unlikely. A simple febrile seizure does not cause brain or neurological damage, learning disabilities, or other disorders.
Febrile seizures and epilepsy
A febrile seizure is different from an epileptic seizure.
If a child has a seizure without a fever, this could indicate epilepsy.
There is a risk of developing epilepsy following a febrile seizure, but it is small.
The chance of a non-febrile seizure disorder, such as epilepsy, developing after one or more simple febrile seizures is between 2 percent and 5 percent, compared with 2 percent in a child who has never had a febrile seizure.
Epilepsy is more likely if:
- There are neurological abnormalities
- There was a developmental delay before febrile seizures started
- There is a family history of epilepsy
- The seizures are complex
- The seizure occurred within an hour of the onset of fever.
Preventing febrile seizures
Doctors do not generally recommend taking anti-seizure medication following a febrile seizure, because the effect of taking medication long term is greater than that of a seizure, which is normally harmless and relatively rare.
A doctor may prescribe medication for a child who has long febrile seizures.
If a child has a fever, acetaminophen or ibuprofen can help to bring it down.