What condition looks like epilepsy, is frequently called “epilepsy,” is frequently counted as epilepsy in epidemiologic studies, but in general has a different basis from that of epilepsy and is seldom treated as epilepsy? The answer is acute symptomatic seizures, also referred to as reactive seizures, provoked seizures, or situation-related seizures. Acute symptomatic seizures are seizures that occur at the time of a systemic insult or in close temporal association with a documented brain insult.^7,8,16 This class of seizure falls into the category of situation-related seizures in the Revised Classification of Epilepsies and Epileptic syndromes suggested by the International League Against Epilepsy.⁷

Acute symptomatic seizures differ from epilepsy in several important aspects: First, unlike epilepsy, these seizures have a clearly identifiable proximate cause, to the extent that one can never be certain of a causal association. When one considers the temporal sequence of acute symptomatic seizures (e.g., uremia, head injury, or stroke immediately preceding a seizure), the biologic plausibility (acute disruption of brain integrity or metabolic homeostasis) and in many cases the dose effect (severity of injury correlated with the risk for seizures) all quite compellingly indicate causation. Although a risk ratio for the immediate association between cause and effect has not been calculated, it must be enormous. Second, unlike epilepsy, acute symptomatic seizures are not characterized by a tendency to recur. The risk for subsequent epilepsy may be increased in individuals experiencing such insults; in general, one does not expect seizures to recur unless the underlying condition recurs. As a corollary, such individuals usually do not need to be treated with antiseizure medication on a long-term basis, although such treatment may be warranted on a short-term basis until the acute condition is resolved.³⁴

Few epidemiologic studies report the frequency of acute symptomatic seizures. This may be caused in part by the difficulties involved in identification. Such seizures are seldom indexed as acute symptomatic seizures; rather, the underlying condition is likely to be diagnosed and coded. This makes a study design relying on medical record review inefficient and probably leads to gross underenumeration. Individuals with acute symptomatic seizures are seldom referred to neurologists for long-term follow-up, and given the acute nature of the condition, an electroencephalographic evaluation may not be warranted or appropriate. These important sources of patient identification are thus eliminated. In studies relying on field surveys, a moderate amount of sophistication is necessary to distinguish acute symptomatic seizures from unprovoked seizures. Thus, even though causation and prognosis of acute symptomatic seizures are quite different from those of epilepsy, some recent epidemiologic studies have categorized individuals with such seizures as having “epilepsy,”³¹ have failed to distinguish between unprovoked and acute symptomatic seizures,²⁸ or have not provided detailed information on cause, age, or gender.^13,20,21 To study acute symptomatic seizures properly, it is more efficient to study the associated conditions, such as head injury or stroke. This procedure is not usually undertaken by most epileptologists, and seizures are not a major interest to specialists treating underlying conditions such as stroke or hyponatremia. Nonetheless, in aggregate, acute symptomatic seizures account for more than half, and in some geographic areas as much as 80%, of all newly occurring seizures. Failure to consider these conditions separately will greatly modify the apparent epidemiologic characteristics of what is called “epilepsy.” In addition to greatly increasing the apparent incidence of “epilepsy” mortality, age and gender structure of those affected is quite different if such cases were included as epilepsy, as has been suggested by some.^14,18,27 At present, acute symptomatic seizures continue to be a useful concept for classification and prognosis, and the suggestions by some that the term (and presumably the concept) be abolished seems inappropriate.

A major difficulty with acute symptomatic seizures remains their definition. For conditions such as stroke or brain trauma, seizures occurring in the first week of an insult have generally been classified as acute symptomatic. This is clearly an artificial cut-point of convenience and would better include all seizures occurring until the point of clinical stabilization. For metabolic conditions, it is frequently unclear for systemic metabolic derangements how severe a derangement must be or for what duration it must persist. For some conditions (e.g., neurocysticercosis), the acute insult may persist for weeks or months, defying a strict temporal definition.¹¹ This chapter reviews the incidence of acute symptomatic seizures and the incidence of seizures in conditions associated with acute symptomatic seizures. Although febrile seizures in childhood are by definition acute symptomatic seizures, they differ from other acute symptomatic seizures in their unique age specificity, high frequency in the population (up to 9%), and universality of exposure. It therefore seems appropriate that they be discussed separately.