The epilepsies are chronic neurological disorders in which clusters of nerve cells, or neurons, in the brain sometimes signal abnormally and cause seizures. Neurons normally generate electrical and chemical signals that act on other neurons, glands, and muscles to produce human thoughts, feelings, and actions.
During a seizure, many neurons fire (signal) at the same time—as many as 500 times per second, much faster than normal. This surge of excessive electrical activity happening at the same time causes involuntary movements, sensations, emotions, and behaviors and the temporary disturbance of normal neuronal activity may cause a loss of awareness.
Epilepsy can be considered a spectrum disorder because of its different causes, different seizure types, its ability to vary in severity and impact from person to person, and its range of co-existing conditions. There also are many different types of epilepsy, resulting from a variety of causes. Recent adoption of the term “the epilepsies” underscores the diversity of types and causes:
About 2.3 million adults and more than 450,000 children and adolescents in the U.S. currently live with epilepsy. Each year, an estimated 150,000 people are diagnosed with epilepsy. In the U.S. alone, the annual costs associated with the epilepsies are estimated to be $15.5 billion in direct medical expenses and lost or reduced earnings and productivity.
Anyone can develop epilepsy. Epilepsy affects both males and females of all races, ethnic backgrounds, and ages. However, Black Americans are more likely to be diagnosed with epilepsy than white Americans due to contributing factors, such as strokes.
According to the U.S. Census Bureau and the Centers for Disease Control and Prevention (CDC), 578,000 Black Americans have epilepsy or a seizure disorder. Over 25,000 Black Americans are diagnosed with seizures or epilepsy each year.
The epilepsies have many possible causes, but as about half people living with epilepsy do not know the cause. In other cases, the epilepsies are clearly linked to genetic factors, developmental brain abnormalities, infection, traumatic brain injury (TBI), stroke, brain tumors, or other identifiable problems. Anything that disturbs the normal pattern of neuronal activity—from illness to brain damage to abnormal brain development—can lead to seizures.
The epilepsies may develop because of an abnormality in brain wiring, an imbalance of nerve signaling in the brain (in which some cells either over-excite or over-inhibit other brain cells from sending messages), or some combination of these factors. In some pediatric conditions abnormal brain wiring causes other problems such as intellectual impairment.
In other people, the brain’s attempt to repair itself after a head injury, stroke, or other problem may inadvertently generate abnormal nerve connections that lead to epilepsy. Brain malformations and abnormalities in brain wiring that occur during brain development may also disturb neuronal activity and lead to epilepsy.
Genetic mutations may play a key role in the development of certain epilepsies. Many types of epilepsy affect multiple blood-related family members, pointing to a strong inherited genetic component. In other cases, gene mutations may occur spontaneously and contribute to development of epilepsy in people with no family history of the disorder (called “de novo” mutations). Overall, researchers estimate that hundreds of genes could play a role.
Several types of epilepsy have been linked to mutations in genes that provide instructions for ion channels, the “gates” that control the flow of ions in and out of cells to help regulate neuronal signaling. For example, most infants with Dravet syndrome, a type of epilepsy associated with seizures that begin before the age of one year, carry a mutation in the SCN1A gene that causes seizures by affecting sodium ion channels.
Genetic mutations have been linked to disorders known as the progressive myoclonic epilepsies, which are characterized by ultra-quick muscle contractions (myoclonus) and seizures over time. For example, Lafora disease, a severe, progressive form of myoclonic epilepsy that begins in childhood, has been linked to a gene that helps to break down carbohydrates in brain cells.
Mutations in genes that control neuronal migration—a critical step in brain development—can lead to areas of misplaced or abnormally formed neurons, called cortical dysplasia, in the brain that can cause neurons to misfire and lead to epilepsy.
Other genetic mutations may not cause epilepsy, but may influence the disorder in other ways. For example, one study showed that many people with certain forms of epilepsy have an abnormally active version of a gene that results in resistance to anti-seizure drugs. Genes also may control a person’s susceptibility to seizures, or seizure threshold, by affecting brain development.
Epilepsies may develop as a result of brain damage associated with many types of conditions that disrupt normal brain activity. Seizures may stop once these conditions are treated and resolved. However, the chances of becoming seizure-free after the primary disorder is treated are uncertain and vary depending on the type of disorder, the brain region that is affected, and how much brain damage occurred prior to treatment. Examples of conditions that can lead to epilepsy include:
Cerebral palsy or other developmental neurological abnormalities may also be associated with epilepsy. About 20 percent of seizures in children can be attributed to developmental neurological conditions. Epilepsies often co-occur in people with abnormalities of brain development or other neurodevelopmental disorders. Seizures are more common, for example, among individuals with autism spectrum disorder or intellectual impairment. In one study, a third of children with autism spectrum disorder had treatment-resistant epilepsy.
Seizure triggers do not cause epilepsy but can provoke “first seizures” in those who are susceptible or can cause seizures in people with epilepsy who otherwise experience good seizure control with their medication. Seizure triggers include:
In surveys of people with epilepsy, stress is the most commonly reported seizure trigger. Exposure to toxins or poisons such as lead or carbon monoxide, street drugs, or even excessively large doses of antidepressants or other prescribed medications also can trigger seizures.
Sleep deprivation is a powerful trigger of seizures. Sleep disorders are common among people with the epilepsies and appropriate treatment of co-existing sleep disorders can often lead to improved control of seizures. Certain types of seizures tend to occur during sleep, while others are more common during times of wakefulness, suggesting to physicians how to best adjust a person’s medication.
For some people, visual stimulation can trigger seizures in a condition known as photosensitive epilepsy. Stimulation can include such things as flashing lights or moving patterns.
Seizures are divided into two major categories: Focal seizures and generalized seizures. However, there are many different types of seizures in each of these categories. In fact, doctors have described more than 30 types.
Focal seizures originate in just one part of the brain. About 60 percent of people with epilepsy have focal seizures. These seizures are frequently described by the area of the brain in which they originate. Many people are diagnosed with focal frontal lobe or medial temporal lobe seizures.
In some focal seizures, the person remains conscious but may experience motor, sensory, or psychic feelings (for example, intense dejà vu or memories) or sensations that can take many forms. The person may experience sudden and unexplainable feelings of joy, anger, sadness, or nausea. He or she also may hear, smell, taste, see, or feel things that are not real and may have movements of just one part of the body, for example, just one hand.
In other focal seizures, the person has a change in consciousness, which can produce a dreamlike experience. The person may display strange, repetitious behaviors such as blinks, twitches, mouth movements (often like chewing or swallowing, or even walking in a circle). These repetitious movements are called automatisms. More complicated actions, which may seem purposeful, can also occur involuntarily. Individuals may also continue activities they started before the seizure began, such as washing dishes in a repetitive, unproductive fashion. These seizures usually last just a minute or two.
Some people with focal seizures may experience auras—unusual sensations that warn of an impending seizure. Auras are usually focal seizures without interruption of awareness (e.g., dejà vu or an unusual abdominal sensation) but some people experience a true warning before an actual seizure. An individual’s symptoms, and the progression of those symptoms, tend to be similar every time. Other people with epilepsy report experiencing a prodrome, a feeling that a seizure is imminent lasting hours or days.
The symptoms of focal seizures can easily be confused with other disorders. The strange behavior and sensations caused by focal seizures also can be mistaken for symptoms of narcolepsy, fainting, or even mental illness. Several tests and careful monitoring may be needed to make the distinction between epilepsy and these other disorders.
Generalized seizures are a result of abnormal neuronal activity that rapidly emerges on both sides of the brain. These seizures may cause loss of consciousness, falls, or massive muscle contractions. The types of generalized seizures and their effects include:
Not all seizures can be easily defined as either focal or generalized. Some people have seizures that begin as focal seizures but then spread to the entire brain. Other people may have both types of seizures but with no clear pattern.
Some people recover immediately after a seizure, while others may take minutes to hours to feel as they did before the seizure. During this time, they may feel tired, sleepy, weak, or confused.
Following focal seizures or seizures that started from a focus, there may be local symptoms related to the function of that focus. Certain characteristics of the post-seizure (or post-ictal) state may help locate the region of the brain where the seizure occurred. A classic example is called Todd’s paralysis, a temporary weakness in the part of the body that was affected depending on where in the brain the focal seizure occurred. If the focus is in the temporal lobe, post-ictal symptoms may include language or behavioral disturbances, even psychosis. After a seizure, some people may experience headache or pain in muscles that contracted.
Just as there are many different kinds of seizures, there are many different kinds of epilepsy. Hundreds of different epilepsy syndromes—disorders characterized by a specific set of symptoms that include epilepsy as a prominent symptom—have been identified. Some of these syndromes appear to be either hereditary or caused by de novo mutations. For other syndromes, the cause is unknown. Epilepsy syndromes are frequently described by their symptoms or by where in the brain they originate.
There are many other types of epilepsy that begin in infancy or childhood. For example:
