Febrile Seizures

Our one-year-old had what the ER doctor called a “febrile seizure” last night. It scared us to death and we want to know how to keep this from ever happening again. Can you help?

We understand why you were scared to death. It’s a terrifying thing to watch your child have a seizure and to feel helpless to stop it. And yes, we can help by explaining what we know of this problem and by providing you with some guidance and importantly, some reassurance.

A febrile seizure refers to an episode that occurs in infancy or childhood, usually between the ages of six months and five years. It is associated with a fever, but without evidence of anything serious going on in the brain. And it’s not a form of epilepsy. In order to be considered a “febrile seizure,” there are a few things that need to be present:

• A seizure associated with an elevated temperature greater than 100.4 degrees (all temperatures are expressed in Fahrenheit degrees)
• Your child has to be older than 6 months and younger than 5 years
• No evidence of any brain infection or inflammation
• No evidence or history of any medical problems that might precipitate seizure activity (kidney disease, diabetes)
• There is no history of any seizure activity without a fever (epilepsy)

Essentially, this an episode of seizure activity in a child who has previously enjoyed good health.

These febrile seizures are divided into two categories, simple and complex. This is important to know, since the type of seizures tells us a lot about what to expect in the future.

A simple febrile seizure is the more common of the two, and is described as being generalized. This means a child’s body is jerking all over – arms, legs, torso. It should last less than 15 minutes and should not happen again within a 24-hour period. Most don’t last more than 5 minutes, and some experts now use 10 minutes as the cut-off. If it’s your child, 5 minutes is going to be an eternity. Should this happen, keep an eye on the clock (if you’re calm enough to do so) and note the duration, since this will be important information for your physician.

A complex febrile seizure is defined as having a focal onset, which means the initial shaking starts in one arm, one leg, or one side of the body. It lasts longer than 15 minutes or occurs more than once in a 24 hour period. This type of febrile seizure is associated with a higher rate of recurrence and a slightly increased rate of epilepsy. We’ll consider that in more detail a little later.

I had never heard of this until our boy had one. How common is it?

This is the most common neurologic problem of infants and children and occurs in somewhere between 2 and 4 percent of children younger than five years of age. That’s about 4 in every 100 children. As a comparison, appendicitis occurs in 2 of every 10,000 children under the age of 4 years. So this is common, and it affects boys slightly more than it does girls.

The risk factors include:

• A young age. This is an age-dependent problem, since an infant’s or toddler’s brains are still developing and their seizure threshold (the point at which a fever occurs) is lower due to this immaturity.
• High fever. We mentioned that the elevated temperature needs to be above 100.4, but the usual temperatures we see will be higher—somewhere around 103 or a little more. We were taught (as are most new physicians) that it’s not the height of the fever that’s important, but the rate of rise of the temperature. It turns out that there’s no evidence to support that view. The height of the fever is apparently the culprit here. That will be important to keep in mind when we talk about how to prevent these seizures.
• The presence of infection. Most commonly, this will be a virus. If it’s caused by a bacteria, we need to be more concerned about an infection that involves the brain or its lining. The type of virus is not important, though there are several that cause most of these seizures. While that’s interesting, we’re not going to have this information when your child comes into the ER or the doctor’s office.
• Recent immunizations. The risk for this is increased with certain vaccinations, including the ones for diphtheria, tetanus, and pertussis, as well as the MMR. This risk is minimal, and if a child has a febrile seizure following an immunization, most experts would recommend repeat vaccinations in the future, since the benefits of doing so will outweigh the risks.
• We’re not sure why, but there is a clear genetic predisposition for febrile seizures. That 4 % incidence we noted early can be as high as 20% if a child’s parents had febrile seizures. That same 20% number is true for the brother or sister of a child who experiences one.
• Prenatal exposure to nicotine (smoking and now “vaping”) causes a slight increase in risk, but there’s no apparent link with alcohol.
• Allergic-type problems, such as eczema, allergic rhinitis, and even asthma. This is interesting, but the increased risk is only minimal.

So what does this look like? Again, we know the age range, and it seems that the greatest risk is between the ages of 12 and 18 months. The majority of these seizures occur on the first day of illness, and sometimes it will be the first sign that your child is sick. With a “simple febrile seizure,” we will see a generalized shaking, with facial and respiratory muscles commonly involved. This can last up to 15 minutes, but fortunately the usual duration is only 3 to 4 minutes. Your child will quickly return to their normal baseline, though some confusion, agitation, or drowsiness might persist for a short time—up to 30 minutes or so. Longer than that and we will be concerned that something else is going on. When a seizure is over, the shaking will stop and your child’s eyes should be closed with their breathing slow and deep. If their eyes remain open and they’re looking off to one side, their seizure probably hasn’t stopped.

“Complex seizures” frequently occur in younger infants, and more so in those with developmental abnormalities/delay. Again, we’ll see shaking in one arm or leg and it will last more than 15 minutes. Another important reason to try to note the time of onset and duration of the seizure.

How will I know it’s a seizure and not something else? 

It’s going to be hard to miss this problem. However, parents (and even physicians) can misinterpret the involuntary movements of “shaking chills” for a febrile seizure. The tip-off is that shaking chills are much more common and usually involve milder, more rhythmic movements around a joint (shoulders, elbows, wrists). We’re not going to see facial involvement with a shaking chill, nor that of the respiratory muscles. Both sides of the body are usually involved at the same time, but there will not be a loss of consciousness. Another clue is that you should be able to stop the shaking of a chill by placing your hands on the involved joints/extremities of your child. You won’t be able to do this with a febrile seizure.

The ER doctor ordered a bunch of lab work and talked about doing a lumbar puncture. He was about to send our son to radiology to get a CT scan of his head, but by then Jeffy was wide awake and running around the room. We said no to that other stuff, and took him home. Did we do the right thing?

It sounds like it. Remember the points that define this condition: age range, no evidence of any serious infection, some degree of fever, previous good health. If all those are present, coupled with a normal exam and quick return to their previous condition, we’ve probably got the diagnosis. A lumbar puncture is not needed in most well-appearing children and should only be done if there is evidence or significant suspicion of possible meningitis. And a CT scan or MRI is not going to be required in these children who quickly return to a normal baseline. If you find yourself in the emergency department, the challenge is going to be to have an open discussion with the ER doctor about the need for any invasive studies or excessive radiation exposure. A significant part of their motivation will be based on a perceived medico-legal risk. Unfortunate, but true. Another reason to know as much about this as possible.

Most of the time, a febrile seizure has ended on its own when the child gets to the doctor’s office or ER, and the child has quickly returned to their normal baseline. If you called 911 and your boy was taken to the ER by ambulance, in some areas of the country, the paramedics may use anti-seizure medication, given as a shot or through an IV line. That’s okay, but the drowsiness caused by the medication will make evaluation a little more difficult and will take longer. But most of the time, the child has stopped seizing before EMS gets to the house and this medication is not needed. The good news is that with a simple febrile seizure and a normal exam, most children don’t require hospitalization and can safely be sent home.

But what if it happens again?

There’s a risk of that, since children with a febrile seizure have an increased chance of having another one. Maybe more than one. Here’s what one large study found:

• The overall rate of recurrence is about 35%.
• The risk varies with age, from 50-65% in children younger than one year, to as low as 20% in those older.
• 50-75% of recurrences happen within one year of the initial seizure.
• Almost all recurrences will happen within two years.

So recurrence is common—about one in three children. There are some factors that when present, can help us identify the child most at risk.

• A young age at onset. Closer to that 6 month cut-off.
• A history of febrile seizures in a parent or sibling.
• A low degree of fever while in the office or emergency department.
• A short duration of time between the onset of fever and the initial seizure.

If a child has all four of these factors, their risk of having a recurrence is high, upwards of 70%. This compares with a risk of only 20% in the child who has none.

For children who have had one or more febrile seizures, the use of fever medication early on in a febrile illness may make the child feel better—even lower their temperature—but it doesn’t appear to lower the incidence of another seizure. That’s troubling, and frustrating. As parents, we want to do something—we want to prevent another of those alarming and distressing events. It’s still reasonable to give your child acetaminophen or ibuprofen if they’re running a fever and are uncomfortable, but it’s not going to stave off another seizure. The good news is that most of the time (at least 66%), your child is not going to have a recurrence. The odds are even better if none of those risk factors noted above are present.

I read somewhere that if a child had a febrile seizure, they would be more likely to develop epilepsy when they get older. Is that true?

Probably. But the risk is only slightly more than those who never have a febrile seizure. The risk is greatest in those children who have complex febrile seizures (focal and prolonged) and those who have repeated seizures during the first 24 hours of the same illness. But again, the overall risk is small.

The bottom line is that febrile seizures are terrifying. We know that. And if your child has ever had one, you know that too. But be reassured, in its most common and “simple” form, this is frequently a “one-and-done” kind of problem. And if there’s a recurrence, it can be managed and doesn’t mean your child is destined to have a life-long seizure disorder.

Knowledge. It’s really going to help us with this one. And it will be reassuring.

“It is the absence of facts that frightens people…” ~Hilary Mantel