ESSENTIALS OF DIAGNOSIS
Paroxysmal spells with sudden onset; generally brief (lasting <5 minutes)
Presentation varies across populations and age groups, ranging from subtle staring to generalized shaking and falling down
Episodes are stereotyped
Diagnosis often depends on eyewitness account
Epilepsy—defined by recurrent, unprovoked seizures
Status epilepticus—defined by prolonged seizures (lasting >5 minutes)
Seizures are episodes of temporary brain dysfunction secondary to abnormal electrical activity. They are common, affecting approximately 10% of individuals at some point in their lives. Approximately 25% of seizures have a clearly identifiable, temporally associated cause. These seizures, labeled acute symptomatic seizures or provoked seizures, do not have a tendency to recur, unless the underlying condition returns.
In contrast, epilepsy is defined as two or more unprovoked seizures (ie, having no identifiable acute, proximal cause). Individuals with epilepsy have a significantly increased risk of recurrent seizures. According to the World Health Organization, epilepsy is the most common primary disorder of the brain. More than 2.3 million people in the United States have epilepsy, and an estimated 181,000 Americans are diagnosed with the disorder each year.
In industrialized countries, epilepsy has an age-specific incidence, highest in the very young and the very old (Figure 7–1). This finding has important implications. As the US population ages, it is expected that the prevalence of epilepsy will also increase. This finding also mirrors what are well-established risk factors for epilepsy. Disorders manifesting in the very young (eg, cerebral palsy and mental retardation) and diseases of the elderly (eg, clinically detected stroke and Alzheimer dementia) increase an individual’s risk of epilepsy by more than 10-fold (Figure 7–2).
Age-specific incidence of epilepsy in the United States (y-axis incidence/100,000).
Risk factors for epilepsy. A risk ratio of 1 (baseline) indicates that there is no increased risk. (CP = cerebral palsy; MR = mental retardation.)
Seizures are a common final pathway in a myriad of diseases of the central nervous system (CNS); however, not all individuals with clinically evident brain injury develop epilepsy. Further confounding the situation, many individuals without any clinical evidence of structural or functional brain abnormalities have epilepsy. Epileptogenesis, defined as the process by which a region of brain, over time, becomes hyperexcitable and develops the ability to spontaneously generate seizures, is not well understood. Clinicians still have no means by which they can prevent the development of epilepsy in high-risk individuals, and for almost two thirds of patients, no cause for their epilepsy can be identified.
Some regions of the brain, for example, the hippocampus, entorhinal cortex, and amygdala (which constitute the mesial or middle temporal lobe), appear to be ...