How is EEG used to diagnose seizures?

Electroencephalography (EEG) Clinicians can find evidence of abnormal electrical activity in the brain and figure out the type or types of seizures a patient is having, as well as the origin(s), by measuring brain waves over minutes to a couple of hours.

What is considered seizure activity?

What is a seizure? A seizure is a burst of uncontrolled electrical activity between brain cells (also called neurons or nerve cells) that causes temporary abnormalities in muscle tone or movements (stiffness, twitching or limpness), behaviors, sensations or states of awareness.

What is a normal EEG result?

Most waves of 8 Hz and higher frequencies are normal findings in the EEG of an awake adult. Waves with a frequency of 7 Hz or less often are classified as abnormal in awake adults, although they normally can be seen in children or in adults who are asleep.

What is spike-and-wave in EEG?

Spike-and-wave is a pattern of the electroencephalogram (EEG) typically observed during epileptic seizures. A spike-and-wave discharge is a regular, symmetrical, generalized EEG pattern seen particularly during absence epilepsy, also known as ‘petit mal’ epilepsy.

How far back can an EEG detect a seizure?

EEG: If performed within 24-48 hours of a first seizure, EEG shows substantial abnormalities in about 70% of cases. The yield may be lower with longer delays after the seizure. If the standard EEG is negative, sleep-deprived EEG will detect epileptiform discharges in an additional 13-31% of cases.

What does a seizure look like on a EEG?

Certain other patterns indicate a tendency toward seizures. Your doctor may refer to these waves as “epileptiform abnormalities” or “epilepsy waves.” They can look like spikes, sharp waves, and spike-and-wave discharges.

Can an EEG show if you had a seizure?

An EEG can usually show if you are having a seizure at the time of the test, but it can’t show what happens to your brain at any other time. So even though your test results might not show any unusual activity it does not rule out having epilepsy. Some types of epilepsy are very difficult to identify with an EEG.