An Elusive Cause
There are so many explanations for how fever might trigger seizures that it's hard to know which is ultimately responsible. And doctors continue to study and debate why some fevers cause seizures in some children and others do not. For many years the accepted wisdom was that febrile seizures are brought on by a fast-spiking fever -- and that it is the speed of a fever's rise, not how high it rises, that causes the electrical surge in the brain. Recent research has called this notion into question, though most febrile seizures do occur while the temperature is rising -- usually in the first 24 hours of an illness.
A high temperature can itself increase "excitability" in the brain, making it more prone to electrical outbursts, and kids' brains tend to respond to illnesses with a higher temperature than do adults' brains. And neurons are more excitable when rapid breathing disrupts the balance of oxygen and carbon dioxide in the brain. Doctors are also focused now on the role of cytokines in seizures. These are a kind of protein, released by the immune system in response to illness, that both increase electrical activity between neurons and turn up our internal thermostat.
While seizures more commonly appear with a higher fever, there does not seem to be a "minimum" temperature required to trigger one. "A febrile seizure is likely caused by a combination of the rate of a fever's rise and individual susceptibility," Dr. Joshi explains. Some kids are simply more vulnerable to febrile seizures and at a higher risk of getting subsequent ones. What's more, certain viral illnesses are more likely to cause febrile seizures; roseola and ear infections seem to be the most common culprits, says Dr. Joshi. Febrile seizures are far more often the result of a virus than a bacterial infection. This could be due to the unique set of cytokines triggered by the different types of germs.