History and exam

Key diagnostic factors

common

febrile illness

A body temperature of 100.4°F (38°C) or above, taken immediately before or at seizure onset, is often regarded as a significant fever in the diagnosis, but some children may have febrile seizures at lower temperatures.[1] [21][65]

seizure

Usually accompanied by a high temperature and soon after with loss of consciousness and generalized tonic-clonic seizure lasting <15 minutes.

Consciousness is recovered quickly, within 30 minutes.

No sequelae.

Less commonly, some seizures are prolonged, focal, or multiple, and recovery of consciousness is delayed.

Other diagnostic factors

common

normal postictal exam

Neurologic exam normal postictally.

Risk factors

strong

temperature elevation

The risk almost doubles for each degree above 100°F (37.8°C).[22][23]

The threshold convulsive temperature varies with the individual, age, and genetic and environmental factors.

young age

Incidence is rare under 6 months and after the fifth birthday; 60% of first seizures occur by the second birthday, 80% by the third, and 95% by the fifth.[12]

May be explained by age-related susceptibility and exposure to certain viral infections and changes in brain maturation.[12]

family history of febrile seizures

Family and twin studies confirm a strong genetic component underlying the risk for febrile seizures.[25] Genes have been identified for some epilepsy syndromes, but specific genes for “simple” or self-limited febrile seizures have been difficult to identify.[26]

The most consistently identified risk factor for febrile seizure is the presence of a close family history (within first-degree relatives) of febrile seizure. The more relatives affected, the greater the risk. In cohorts of children with febrile seizure, the risk that siblings will have a febrile seizure is 10% to 45%.[6]

viral or bacterial infection outside the central nervous system

Bacterial infection (e.g., otitis media) is sometimes the source of fever.

Certain viruses (i.e., human herpesvirus-6 and influenza A) are associated with a relatively high incidence of febrile seizures.

Viral infections occur with equal frequency in febrile patients with or without seizures, and factors other than the virus may explain the tendency to have a seizure.

Multiple factors, including proinflammatory cytokines and immune response, may be involved, temperature elevation being the essential trigger.[11][24][27]

weak

male sex

Boys are affected more than girls, with a ratio of 1.6 to 1.[7]

vaccinations

The measles, mumps, and rubella (MMR) vaccine accounted for 25 to 34 cases per 100,000 children and the diphtheria, tetanus, and pertussis (DTP) vaccine accounted for 6 to 9 cases per 100,000 children.[28]

Highest risk on the day of vaccination with DTP and at 7 to 14 days after vaccination with MMR, coincident with a febrile period.[28][29] [ Cochrane Clinical Answers logo ]

The risks declined significantly with the introduction of acellular pertussis vaccine (1997-1998), whereas frequency related to MMR showed no significant change between 1995 to 1996 and 1998 to 2001.[30]

MMR-varicella combination vaccine is associated with a greater risk of seizures than MMR and varicella vaccines administered separately.[31]

Vaccination with the combined diphtheria-tetanus toxoids-acellular pertussis-inactivated poliovirus-Haemophilus influenzae type b (DTaP-IPV-Hib) vaccine is associated with a small increase in the risk of febrile seizures on the day of administration at 3 and 5 months of age, but not when the vaccine is given at 12 months of age.[32]

Risk of fever and seizure following a measles-containing vaccine is significantly lower when administered at 12 to 15 months than at 16 to 23 months of age.[33]

prenatal exposure to nicotine

Slightly increased risk in children if mothers smoked 10 or more cigarettes a day during pregnancy.[34]

No documented association with maternal alcohol and coffee consumption.[34]

iron deficiency

Iron insufficiency has a possible role in the occurrence of first seizures.[35]

Mean ferritin levels were significantly lower in affected children than in controls (29.5 versus 53.3 micrograms/L; P = 0.0001).[35] Lower levels of hemoglobin and mean corpuscular volume were not significantly different.

Two meta-analyses suggested that iron-deficiency anemia is associated with an increased risk of febrile seizures in children.[36][37]

complications of pregnancy, labor, and delivery

In a large pediatric population followed prospectively, complications of labor and delivery were not important risk factors.[38]

Fetal growth retardation is associated with an increased risk of febrile seizures.[39]

In a community-based prospective case-control study, prenatal and perinatal risk factors were compared. There were no differences between cases and controls in factors occurring during delivery such as occurrence of acute or elective cesarean section, signs of fetal distress in amnion fluid, abnormalities of fetal heart rate, or duration of delivery. Perinatal asphyxia was uncommon and there was no difference between cases and controls.[40]

Use of this content is subject to our disclaimer