Most febrile seizures occur because of a sudden spike in body temperature, and most occur during the first day of a fever.

Viral or bacterial infection

Usually, the fevers that trigger febrile seizures are caused by a bacterial or viral infection in your child's body. Typical childhood illnesses, including respiratory illnesses and infections such as roseola — a viral illness that causes swollen lymph nodes, usually in the neck, and a rash — are often associated with febrile seizures. A less common but very serious cause of sudden fever with seizures is an infection of a child's brain and spinal cord (central nervous system), such as meningitis or encephalitis. These illnesses may also cause seizures without a fever.

Post-immunization seizures

The risk of febrile seizures may increase after some childhood immunizations, such as the diphtheria, tetanus and pertussis (DTP) or measles-mumps-rubella (MMR) vaccinations. Low-grade fevers can sometimes occur after your child receives childhood vaccines. If a febrile seizure occurs, it's caused by the fever that may accompany the vaccination — not by the vaccination itself.

Jan. 24, 2012