A febrile seizure is a convulsion in a child triggered by a fever. Such convulsions occur without any underlying brain or spinal cord infection or other neurologic cause.

About 3-5% of otherwise healthy children between the ages of 9 months and 5 years will have a seizure caused by a fever. Toddlers are most commonly affected. There is a tendency for febrile seizures to run in families. Most occur well within the first 24 hours of an illness, not necessarily when the fever is highest. The seizure is often the first sign of a fever.

The first febrile seizure is one of life's most frightening moments for parents. Most parents are afraid that their child will die or have brain damage. Thankfully, simple febrile seizures are harmless. There is no evidence that simple febrile seizures cause death, brain damage, epilepsy, mental retardation, a decrease in IQ, or learning difficulties.

Most febrile seizures are triggered by fevers from viral upper respiratory infections, ear infections, or roseola. Meningitis causes less than 0.1% of febrile seizures but should ALWAYS be considered, especially in children less than one year old or those who still look ill when the fever comes down.

A simple febrile seizure stops by itself within a few seconds to 10 minutes, usually followed by a brief period of drowsiness or confusion. Anticonvulsant medicines are generally not needed.

A complex febrile seizure is one that lasts longer than 15 minutes, occurs in an isolated part of the body, or recurs during the same illness.

About a third of children who have had a febrile seizure will have another one with a subsequent fever. Of those who do, about half will have a third seizure. Few children have more than three febrile seizures in their lifetime.

If there is a family history, if the first seizure happened before 12 months of age, or if the seizure happened with a fever below 102, a child is more likely to fall in the group that has more than one febrile seizure.

A febrile seizure may be as mild as the child's eyes rolling or limbs stiffening. Quite often a fever triggers a full-blown convulsion that involves the whole body.

Febrile seizures may begin with the sudden sustained contraction of muscles on both sides of a child's body -- usually the muscles of the face, trunk, arms, and legs. A haunting, involuntary cry or moan often emerges from the child, from the force of the muscle contraction. The contraction continues for seemingly endless seconds, or tens of seconds. The child will fall, if standing, and may pass urine.

He may vomit. He may bite his tongue. The child may not be breathing, and may begin to turn blue.

Finally, the sustained contraction is broken by repeated brief moments of relaxation -- the child's body begins to jerk rhythmically. The child is unresponsive to the parent's voice.

Febrile seizures are different than tremors or disorientation also seen with fevers. The movements are the same as in a grand mal seizure.

A febrile seizure may be diagnosed by the health care provider when a grand mal seizure occurs in a child with a fever and no prior history of seizure disorders (epilepsy). In infants and young children, it is important to rule out other causes for a first-time seizure, especially meningitis.

In a typical febrile seizure, the examination usually shows no abnormalities other than the illness causing the fever. Typically, a full seizure workup including an EEG, head CT, and lumbar puncture (spinal tap) is not warranted.

However, the child's condition must meet strict medical criteria if these tests are to be avoided:

• The child must be developmentally normal.
• The seizure must be generalized (not focal), meaning more than one part of the body is involved.
• The seizure may not last longer than 15 minutes.
• The child cannot have had more than one febrile seizure in 24 hours.
• The child's neurologic exam performed by a health care provider must be normal to be called a simple febrile seizure.

If all of these criteria are met, no further studies are likely to be required.