What Is a Seizure?

A seizure can be a feeling or, more commonly, a set of behaviors, usually involving shaking of the body and loss of awareness, resulting from a sudden, uncontrolled surge in electrical activity in clusters of nerve cells in the brain. Some patients have behaviors that look like seizures but are not triggered by an abnormal surge in electrical activity in the brain. These events are called non-epileptic seizures.

Diagnostic testing with continuous EEG is the best way to determine whether an action or behavior is due to epileptic seizure. Epileptic seizures can be divided into two categories: those that are provoked by a reversible problem such as elevated blood sugar or acute renal failure, and those that are unprovoked.

The Centers for Disease Control and Prevention estimates that more than 2.2 million people in the United States are affected by epilepsy, seizure disorders or both. If you or someone you love has experienced a seizure, it can be frightening and overwhelming. However, remarkable advancements have been made in the world of neuroscience, and many adults can be treated successfully with a proper diagnosis.

Types of Seizures

The first step in deciding whether someone has epilepsy is making sure that the seizures are an epileptic seizure and not a non-epileptic seizure, such as syncope (fainting) or a psychogenic process. The second step is ruling out a provoked seizure, which can be treated by fixing the underlying issue, such as correcting the amount of sodium in the blood. If the events are epileptic seizures, an effort is made to classify the seizures as generalized or focal.

Generalized seizures occur when electrical impulses spread in both halves of the brain. They include:

  • Myoclonic seizures, which produce sporadic jerking on both sides of the body
  • Absence seizures, which are marked by a short loss of consciousness that produces a “blank stare” and “lost time”
  • Generalized tonic-clonic seizures (formerly called grand mal seizures), in which the person usually loses consciousness and collapses, followed by a stiffening of the body and violent jerking
  • Atonic seizures, which are marked by sudden and general muscle tone loss, usually in the arms and legs

Focal seizures are caused by electrical impulses generated by, and limited to, one hemisphere (half) of the brain. They include:

  • Aura seizures (“warnings” or very small events that occur in isolation or are precursors to larger seizures) – these are focal seizures without impairment in consciousness, involving only psychic phenomenon such as fear or smell.
  • Simple focal seizures – patient retains consciousness and has altered sense of hearing, smelling, tasting, seeing and tactile perception. These are focal seizures without impairment of consciousness or awareness, with observable motor or autonomic components such as arm twitches, hyperventilation, sweating and increased heart rate.
  • Complex focal seizures (impairment of awareness or responsiveness) – these are focal seizures with impairment of consciousness or awareness, or dyscognitive features.
  • A fourth kind of focal seizure that evolves into a generalized seizure – these are focal seizures that evolve to bilateral, convulsive seizures.

Most patients with focal seizures have an abnormal brain region that is triggering the seizures. These seizures can be treated with drugs, but can often be treated successfully with surgery.

Multiregional seizures are focal seizures that come from more than one part of the brain.

What Causes Seizures?

It can be difficult for doctors to identify the exact cause of seizures. They can be classified as either provoked or unprovoked. Provoked seizures are caused by factors such as drug and alcohol use or withdrawal, a lack of sleep, an adverse reaction to medication, a brain tumor, elevated blood sugar or low sodium levels in the blood. In general, such seizures are readily remediable by medical or surgical therapies directed at the provoking factor.

Unprovoked seizures are caused by factors that are not easy to readily correct, such as a congenital brain malformation, scarring from a brain trauma or old stroke, or from a genetic problem. Nonepileptic events can be caused by syncope (fainting spells), movement disorders or psychiatric disorders such as psychogenic non-epileptic spells, conversion disorder or depression.

Seizures vs. Epilepsy

Having a seizure does not necessarily mean a person has epilepsy. There are many reversible causes of seizures, including meningitis and other infections in the brain, hyperglycemia, hypoglycemia, hyponatremia (low salt levels in the blood), drug and alcohol withdrawal, and certain medications. If these problems are resolved, then the seizure does not recur and the person does not have epilepsy. Seizures triggered by these kinds of factors are called provoked seizures. Unprovoked seizures cannot be explained by an obvious reversible problem. A person who experiences more than one unprovoked seizure is typically diagnosed with epilepsy.

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