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Two Populations Are Better than One

Commentary Given that febrile seizures (FSs) are the most common seizure “syndrome” of childhood occurring in 2 to 4 percent of individuals, one would think that clear definitions and descriptors based upon data are available. However, when one digs not very far below the surface, one finds some fundamental gaps. In 1980, the National Institutes of Health (1) convened a consensus conference to approach a number of critical questions such as, “What is a febrile seizure?” as well as attendant risks (injury, repeat febrile and afebrile seizures, benefits and risks of prophylaxis and management). The consensus suggested that these seizures usually occurred between 3 months and 5 years, but otherwise did not provide guidance as to how long the seizures last or any basis for distinguishing those that were prolonged from those that were not. However, a prolonged seizure was identified as one of the important risk factors predisposing the child to afebrile seizures. One of the seminal studies upon which this recommendation was based (and which we have used to counsel our families) defined prolonged as greater than 15 minutes and reported that this will occur in almost 8 percent of children with FS (2). The use of 10 to 15 minutes as the cut-point to identify seizures as prolonged has been adopted by subsequent reports (3–6). What are the implications embedded in the concept of a cut-point ? A meaningful risk factor for afebrile seizures? A marker for current and/or future developmental delay? Does it reveal something about the neurobiology of seizure pathophysiology, and, specifically, termination? The answers to these questions can play a role in how we evaluate children with FS, considerations for acute and prophylactic therapies (especially if anti-epileptogenesis agents become available), referral for developmental services, and creation of novel treatments based on known (and perhaps common) pathophysiologies. So determining seizure duration is not a trivial matter, and the accuracy of 10 to 15 minutes becomes crucial. So how long do FSs really last? If you ask family members who witnessed the event, “It seemed like forever” may be the most common response. Is there any real data? The answer is “Yes,” but only very recently. Hesdorffer et al. (4) prospectively ascertained children with a first FS from the emergency department logs and hospital discharges in a metropolitan medical center spanning the years 1999 to 2004 (4). Information regarding seizure duration and developmental status was obtained from the medical record and parent interviews, in addition to patient demographics and family history. Subsequently, an MRI and formal developmental testing were performed on each child. A total of 158 patients with “complete data on exact seizure duration” were studied. Visual analysis of the plotted seizure durations suggested at least two populations of durations, with the transition point occurring at approximately 10 minutes. In fact, Distribution of Febrile Seizure Duration and Associations with Development.