Febrile Seizures: Evaluation and Treatment
Case 2: Complex Febrile Seizure
A 1-year-old child presents to the emergency department. Mother was with the child and she noticed stiffness followed by jerking of the left arm and leg, which quickly became noted in both arms and legs. The episode appeared to last for 15 minutes before EMS arrived to the house. A medication was given to the child by EMS that stopped the event. EMS noted the child had a temperature of 101.5°F. The child was previously healthy and has had normal development thus far.
What is the epidemiology of complex febrile seizure?
A complex febrile seizure is one with focal onset, or one that occurs more than once during a febrile illness or lasts more than 10 minutes. They are less common, representing only 20% to 30% of all febrile seizures [18–20]. In The National Collaborative Perinatal Project (NCPP), 1706 children with febrile seizures were identified from 54,000 and were followed from birth until 7 years of age. The initial febrile seizure was defined as complex in about 28%. For all febrile seizures, focal features were present in 4%, prolonged duration (> 10 minutes) in 7.6%, and recurrent episodes within 24 hours in 16.2% [21]. Similar observations have been reported by Berg and Shinnar [5,6]. Of 136 children who had recurrences, 41.2% had one or more complex features and the strongest correlate of having recurrent complex febrile seizure was the number of recurrent seizures. They also found that children with complex recurrences had other recurrences that were not complex; however, complex features had a tendency to recur. Further, a strong association between focal onset and prolonged duration was found [5,6]. Previous studies established a correlation between complex attacks, particularly prolonged ones and young age (age < 1 year) [5,6]. Additionally, children with seizures with a relatively low fever (< 102°F) were slightly more likely to have a complex febrile seizure as the initial episode [5,6].
Children with febrile seizures are already at 4- to 5-fold increased risk for subsequent unprovoked seizures. A history of febrile seizures has been found in 13% to 18% of children with new-onset epilepsy. In the NCPP study, the predictors identified for the development of epilepsy following febrile seizures were an abnormal neurological and developmental status of the child before the seizure, a history of afebrile seizures in a parent or prior-born sibling, or complex features [21]. Ten percent of children with 2 or more of the previously mentioned risk factors (including complex features) developed epilepsy and 13% of them had seizures without fever [20,22]. Further, intractable epilepsy and neurological impair-ment have been found to be more common in children with prior prolonged febrile seizure, with no association to any specific seizure type [18,23–25]. The association between febrile seizures and mesial temporal sclerosis (MTS) is a commonly debated topic. Retrospective studies have reported an association between prolonged or atypical febrile seizures and intractable temporal lobe epilepsy. Epidemiological studies fail to show a causal relationship between febrile seizures and temporal lobe epilepsy [26]. This suggests that febrile seizures are a marker of susceptibility to seizures and future epilepsy (in some cases) rather than a direct cause. It is clear that a minority of cases of MTS or complex partial seizures are associated with prior febrile seizures [20,22].
What is the risk of intracranial pathology in complex febrile seizure?
Patients with complex febrile seizures usually seek medical attention [27]. However, the risk of acute pathology necessitating treatment changes based on neuroimaging was found to be very low and likely not necessary in the evaluation of complex febrile seizures during the acute presentation [27]. Imaging with a high-resolution brain MRI could be considered later on a routine basis for prolonged febrile seizures due to the possible association between prolonged febrile seizures and mesial temporal sclerosis [19,28,29].
Neuroimaging has provided evidence that hippocampal injury can occasionally occur during prolonged and focal febrile seizures in infants who otherwise appear normal. It has been speculated that a pre-existing abnormality increases the propensity to focal prolonged seizures and further hippocampal damage. Hesdorffer and colleagues [30] found definite abnormalities on MRI in 14.8% of children with complex febrile seizures and 11.4 % of simple febrile seizures among 159 children with a first febrile seizure. However, MRI abnormalities were related to a specific subtype of complex seizures: focal and prolonged. The most common abnormalities observed were subcortical focal hyperintensity, an abnormal white matter signal, and focal cortical dysplasia.
What are important aspects of the clinical evaluation?
The evaluation and management of the child with complex febrile seizures is debated as well. The most important part in the history and examination is to look for the source of the fever and rule out the presence of a CNS infection, since complex febrile seizures are much more frequently associated with meningitis than simple febrile seizures [16]. The American Academy of Pediatrics recommended that a lumbar puncture be strongly considered in infants younger than 12 months after a first febrile seizure and should be considered in children between 12 and 18 months of age, since signs of meningitis may be absent in young children [13]. If the threshold for a lumbar puncture is low in infants with febrile seizures in general, it should be even lower for children with complex febrile episodes for all the factors mentioned above. The guidelines developed in 1990 by the Royal College of Physicians and the British Paediatric Association concluded that indications for performing an lumbar puncture were complex febrile seizure, signs of meningismus, or a child who is unduly drowsy and irritable or systematically ill [21].
Obtaining an EEG within 24 hours of presentation may show generalized background slowing, which could make identifying possible epileptiform abnormalities difficult [22]. Therefore, a routine sleep deprived EEG when the child is back to baseline can be more useful in identifying if epileptiform abnormalities are present. If epileptiform abnormalities are present on a routine sleep deprived EEG, this may suggest the patient is at higher risk for developing future epilepsy and the febrile illness lowered the seizure threshold; however, it is unclear whether clinical management would change as a result [31].
