Ten percent of children and adolescents with a first seizure presented in SE, comparable to prior studies.1–3,16
The most common etiology was prolonged febrile convulsion, followed by cryptogenic. The most common acute symptomatic cause was CNS infection, and the most common remote symptomatic cause was cerebral dysgenesis. Combined CT and MRI provided a diagnosis in 30% and directed acute management in 24%.
Hypoglycemia and hypocalcemia can be triggers for seizures. In our population, these abnormalities were rare, which may be attributed to the probability that serum electrolytes were checked after the administration of IV fluids with glucose. Although all patients with lumbar punctures had negative CSF cultures, many had CSF pleocytosis, indicating a primary CNS infection. However, postictal pleocytosis up to 12 cells/μL has been observed in patients with repetitive seizure activity and also single seizures.17
In our cohort, 9% of patients with lumbar punctures had CSF leukocytes >12 cells/μL, 22% of which were febrile.
Recent epidemiologic studies argue that febrile convulsions should be a separate entity from acute CSE because they have an overall more favorable prognosis. Moreover, studies that do not separate febrile CSE from acute symptomatic CSE are likely to overamplify the severity of outcome of febrile CSE, thus attenuating the severity of acute neurologic insults.1,18
Previously reported epidemiologic studies on CSE are primarily based on adult populations, which may not be applicable to children.3,10–11,15,19–21
In adults with previously diagnosed epilepsy, AED noncompliance and resultant withdrawal is the most common cause of SE. While pediatric new-onset SE is often due to febrile CSE, the most common causes in adults are acute symptomatic from anoxic injury, acute cerebrovascular events, or CNS infections.5,10–11,15,19–21
These differences are likely because the physical and neurochemical characteristics of the developing brain differ from those of the mature brain.22
Prior pediatric studies have been broad epidemiologic studies, and few have looked specifically at SE, the most recent being the North London study. The North London study has the advantage of being community-based in which patients were identified by telephone interviews, cards, and chart reviews, but is a retrospective design. The patients in our study were prospectively identified upon presentation to a tertiary care hospital, which may confer a different selection bias. Compared to the North London study, our group had fewer cases of prolonged SE, no cases of mortality, and different rates of cryptogenic and idiopathic etiologies. The lower rates of mortality and SE greater than 1 hour at our institution may be representative of out-of-hospital treatment patients receive in the United States en route to the hospital and the early transfer to a tertiary care center. Compared to the pediatric cohort in the Richmond study, our group had a similar age distribution, but varied in seizure type with a lower mortality.19
Compared to a large multicenter study in children, our group had a similar distribution of age, but the younger age group varied in etiology, with cryptogenic and acute symptomatic being more common than remote symptomatic causes, especially in those less than 2 years of age.23
For the evaluation of any child with newly recognized seizures, the Subcommittee of the American Academy of Neurology, Child Neurology Society, and American Epilepsy Society recommends EEG as a standard part of diagnostic investigation, and neuroimaging is considered optional.24
Recent literature emphasizes the yield of prolonged video EEG monitoring in identifying nonconvulsive SE (NCSE), an important subtype of SE, yet difficult to identify and treat. The incidence of NCSE in pediatric patients undergoing long-term monitoring in the intensive care setting ranges from 16 to 32 percent.25–27
In patients who had an EEG for coma, 8% were found to be in NCSE, including 12% of children 18 years of age or younger.28
In our study, all patients with electrographic seizures were captured only with prolonged video monitoring; NCSE was captured in 22% of those with prolonged monitoring. Although this study was not intended to evaluate the yield of prolonged video EEG monitoring, patients in SE may benefit from monitoring, especially if there is a protracted impairment of consciousness, comatose state, or postictal behavior.29
Several studies have addressed the utility of neuroimaging in patients who present with a first-time seizure, with the incidence of abnormalities ranging from 13% to 32%.30–32
Studies have concluded there is little evidence to support routine imaging for those who have no risk factors for epilepsy and that neuroimaging in these patients may not warrant a change in the acute management.31–34
These studies did not address imaging in the context of SE. In a large study of 613 children with newly diagnosed epilepsy, nearly 80% had neuroimaging, with relevant lesions in 13%.30
In our study evaluating neuroimaging in new-onset SE, CT was helpful in identifying acute vascular lesions and acute edema in patients, whereas MRI was superior, particularly in identifying subtle abnormalities and remote symptomatic etiologies. The choice of imaging modality, often debated, depends on urgency, availability, and resolution. However, CT confers radiation exposure that may not be trivial especially for the youngest children.35
Although this study was not intended to directly compare imaging modalities, the results of our cohort of patients with a more severe presentation highlight the importance of neuroimaging to help establish an etiology, inform management, and provide information relevant to long-term prognosis.
Imaging abnormalities must be placed in the context of those of the normal population. The NIH Clinical Center study, one of few large-scale normative imaging studies, reported on 1,000 normal volunteers aged 3–83 years. Fifteen percent had incidental findings that did not require further follow-up or evaluation, 1% had findings that required urgent evaluation, and 1.8% had findings that required routine evaluation.36
In contrast, our study had incidental neuroimaging findings in 6%. It is possible in the NIH study that some patients may have entered the study to obtain an MRI for underappreciated reasons.
One limitation of this study is that with our standardized database SE was defined as a tonic, clonic, or tonic-clonic unremitting seizure lasting greater than 20 minutes, and did not include other definitions, of 2 or more such seizures between which consciousness was not regained (intermittent convulsive SE), or which lasted for at least 30 minutes.6,37
In one study, seizures of 20–29 minutes duration were more likely to stop spontaneously or with medical treatment and have a lower mortality than those ≥30 minutes.38
However, we could not evaluate distinctions based on this time frame.
Understanding the epidemiologic and etiologic basis of pediatric SE is important due to the significant risk of recurrent SE, which has been reported as 11%–16% at 1 year and 18% at 2 years.1,39
Our findings are similar to those outlined in a recent review of the evaluation of pediatric SE.40
This study adds to the literature the evaluation of a child with new-onset seizures that are SE. In this setting, a routine EEG follows the recommended guidelines for new-onset seizures.24
From this study, we cannot determine whether routine EEG is helpful in a patient with a known history of epilepsy or SE. For any child who presents in SE and who has not yet returned to baseline, the possibility of nonconvulsive SE should be considered; these patients may benefit from long-term video EEG monitoring. The use of long-term EEG in both populations merits further study.
We recommend imaging in this population, as a substantial proportion of children had abnormalities that helped establish etiology and direct therapy. The role for imaging in patients with known epilepsy and SE remains undefined. Access to imaging modality varies among institutions. CT is often more widely available, especially in the urgent setting, but may be falsely reassuring and exposes the patient to radiation.35
Due to the superior yield, strong consideration for MRI should be given when available.