The International League Against Epilepsy (ILAE) defines seizures as a transient occurrence of signs or symptoms due to abnormal, excessive, or synchronous neuronal activity in the brain.¹ The ILAE categorizes seizures by the location of onset in the brain: focal, generalized, or unknown; they are subcategorized by the presence or absence of motor symptoms and loss of awareness.¹

In generalized onset seizures, abnormal electrical activity initiates throughout the brain. These types of seizures always include loss of awareness.¹ Focal onset seizures begin in one area of the brain, although they may generalize to involve the entire brain and may or may not include loss of awareness.¹ Motor symptoms can include the classic tonic-clonic movements as well as myoclonus or atonic seizures.¹ Nonmotor symptoms of seizures may include emotional, sensory, and cognitive changes, or a lack of movement due to absence seizures.¹

Most people with a first seizure do not have epilepsy. Epilepsy usually requires two unprovoked seizures occurring at least 24 hours apart, but the diagnosis can be made based on a single unprovoked seizure with at least a 60% risk of a second seizure in the next 10 years, or in the setting of an epilepsy syndrome.² Determining the risk of a second seizure is an important part of the evaluation of the first seizure, although no formula exists to calculate risk and factors should be considered individually.

Epidemiology

The lifetime risk of having a seizure for an adult is up to 10%, although only 3% will be diagnosed with epilepsy.³ The incidence of a first seizure increases with age starting at approximately 55 years, with the highest risk in people older than 75 years.⁴

The rate of first seizures is higher in low-income countries than in the United States.⁵ Low- and middle-income countries account for approximately 80% of epilepsy worldwide. This may be because of higher rates of risk factors for epilepsy, such as congenital conditions, intracranial infections, and traumatic brain injury.⁵ In high-income countries, first seizures are more common in people affected by social and economic deprivation.⁶ Worldwide, seizures are increased where there is inadequate access to health care.⁷

Types of Seizures

ACUTE SYMPTOMATIC (PROVOKED) SEIZURES

Acute symptomatic seizures, also known as provoked or situation-related seizures, are manifestations of an acute insult to the central nervous system. Stroke and central nervous system infection are the most identified provoking factors.⁸ Other provoking factors include metabolic derangements, such as electrolyte abnormalities, or toxic effects of medications, alcohol, or drugs, including overdoses.⁹ Provoking factors may be infectious, inflammatory, metabolic, structural, or toxic in nature¹⁰ (Table 1^11–15).

Approximately 40% of first seizures are associated with provoking factors. The evaluation after a first seizure should focus on identifying these factors¹⁰ (Figure 1^3,7,16–20). This allows for the treatment of an underlying condition, or an assessment of an increased risk of seizure recurrence, to reduce the risk of subsequent seizures.⁷

UNPROVOKED SEIZURES

Unprovoked, or idiopathic, seizures do not have an acute cause identified on evaluation. Unprovoked seizures are most common in younger people.⁸ Unprovoked seizures are more likely to recur than those with a provoking cause found on evaluation.⁹

Unprovoked seizures are divided into two categories: those with no known etiology, and those related to progressive, preexisting, or remote central nervous system injury. Unprovoked seizures with known etiologies include prior traumatic brain injury, congenital cerebral palsy, and remote central nervous system infection.²¹ Unlike in acute symptomatic seizures, the central nervous system insult does not occur within the same time frame as the seizure. Recurrence is more common in unprovoked seizures with known etiologies.²²