Over 10 Conditions Diagnosed With an EGG

An electroencephalogram (EEG) is a noninvasive test that measures certain aspects of brain activity that reflect a person’s level of consciousness. It is used to diagnose epilepsy and certain types of brain damage and is part of a polysomnogram (comprehensive sleep study) that is used to diagnose sleep disorders.

Neurons communicate with each other through electrical signals. The EEG measures the synchrony and rhythm of electrical signals throughout the brain.

10-Plus Conditions Diagnosed With EEG

An EEG test examines the rhythm of brain activity and the symmetry of nerve activity throughout the brain. The pattern of your EEG brain waves differs between waking and sleeping and cycles through stages while you’re sleeping.

Additionally, some medications, such as sedatives (medications that make you drowsy) and anesthetics (medications that reduce pain), can alter a person’s level of consciousness, which can be reflected in an EEG.

Severe brain damage, such as due to brain injury or oxygen deprivation, can cause EEG changes.

Seizures

A common use for EEG is evaluating for epilepsy (a group of neurologic disorders characterized by recurrent seizures). Epilepsy can be confused with non-epilepsy conditions that may produce similar disordered movements. An EEG is very helpful in distinguishing between epilepsy and these conditions.

An EEG would change during an ongoing seizure. Sometimes, EEG changes can be detected interictally (when a seizure is not occurring). In certain situations, an EEG test is accompanied by video recording to correlate the clinical symptoms with the EEG changes.

Additionally, an EEG technician may use techniques that can trigger a seizure to make the test more sensitive. Hyperventilation (breathing really fast) or flashing lights can trigger a seizure. When such techniques are used during an EEG, anti-epilepsy medication is kept nearby in case a seizure develops.

Seizures and seizure-like conditions include:

• Epilepsy: If you experience one or more episodes of involuntary movement or impaired consciousness, an EEG can help in determining whether the episodes are seizures. Different types of epilepsy are associated with specific EEG patterns during a seizure and interictally.
• Psychogenic nonepileptic seizures (PNES): A type of seizure known as PNES involves seizure behavior without seizure activity in the brain. This can be precipitated by anxiety, stress, and other underlying mental health conditions. Usually, an EEG that is used to evaluate potential PNES is done with video monitoring to see if the clinical seizure symptoms correlate with EEG changes.
• Movement disorders: Some movement disorders, such as tics and tremors, appear similar to seizures. The involuntary movements that occur in movement disorders are not associated with EEG changes. Sometimes, EEG is ordered to help distinguish between epilepsy and movement disorders.
• Migraine: Migraine aura, which involves neurological symptoms such as sensory changes, speech impairment, or visual changes, can be part of a migraine episode. The symptoms can be similar to symptoms of a seizure, but migraine does not cause EEG changes. Sometimes, an EEG is ordered to distinguish the two conditions.
• Encephalopathy: Liver failure, kidney failure, and multisystem organ failure can cause substantial disruption of brain functions, which is often diagnosed as encephalopathy. This condition can cause diminished responsiveness and seizures, as well as characteristic alterations in EEG patterns.
• Confusion: There are numerous causes for confusion, including drug or alcohol intoxication, encephalopathy, dementia, epilepsy, stroke, or a psychotic reaction. An EEG can often help identify patterns that guide diagnosis in these situations.

Sleep Disorders

An EEG is part of a polysomnogram sleep study. This type of sleep study also involves monitoring your blood oxygen level, muscle movement, heart rate, and body temperature, which can help diagnose sleep disorders.

Sleep disorders that can be diagnosed with the aid of EEG include:

• Central sleep apnea: This condition is characterized by breathing pauses during sleep due to alterations in brain activity.
• Obstructive sleep apnea: This common sleep disorder is characterized by intermittent episodes of blocked airway flow during sleep. During these episodes, people wake up for a few seconds and then fall asleep again.
• Narcolepsy: This sleep disorder is characterized by abrupt episodes of falling asleep during the day.
• REM (rapid eye movement) sleep behavior disorder: This sleep disorder causes changes in behavior during the dreaming stage of sleep.

Prognosis

Sometimes an EEG is used as a medical assessment of severe brain damage to help in guiding prognosis and understanding expectations for recovery.

EEG uses in prognosis include:

• Prolonged unconsciousness: If your loved one has been unconscious for a long period of time and it’s unclear whether they will be able to recover, an EEG may be used to help determine whether there is significant brain damage.
• Hypoxia: Oxygen deprivation to the brain can cause a type of brain damage that’s described as hypoxic injury. This can happen at any age, including before a baby is born, during extensive blood loss, or as a result of substantial heart or lung failure. Often, an EEG shows patterns of brain activity that can help identify the extent of hypoxic brain injury.
• Brain death: In cases of extensive brain damage, mechanical support can keep body organs functioning, even when the brain does not have viable activity. An EEG can help in assessing whether a person is expected to have a recovery.

Reasons a Provider Orders EEG

You or your loved one may need an EEG test if you’re being evaluated for possible seizures or an unexplained change in mental status. If you have a polysomnogram to evaluate a sleep disorder, an EEG is usually part of this test.

Typically, EEG testing is ordered by a neurologist, psychiatrist, intensive care physician, emergency medicine physician, or sleep specialist. Sometimes, in special circumstances, other healthcare providers may order an EEG, but insurance providers usually require an order from a physician.

Timing of Test

The timing of an EEG test can be important, particularly in relation to sleep. Sleep deprivation can trigger a seizure in people who have epilepsy. An EEG that’s done for epilepsy evaluation may be more likely to detect signs of epilepsy if a person has not had a full night’s sleep.

You may be instructed to stop taking certain medications prior to an EEG if those treatments are expected to make the results less reliable.

If you’re having a polysomnogram for evaluation of a possible sleep disorder, you may be asked to sleep as you normally do the night before your study and then to stay awake throughout the rest of the day before your evening sleep study.

Polysomnograms for some sleep disorders, such as narcolepsy, may be done during the day to assess daytime sleepiness.

EEG Accuracy

Many factors determine the accuracy of an EEG. You will be instructed to try to lie still without moving during the study. Movement can often make the results unreliable.

Anti-epilepsy medications can suppress seizure activity and may sometimes make it less likely to identify seizure patterns.

Medications used for sedation can suppress brain activity. These medications are often discontinued before or during the EEG, so the study will provide an accurate reflection of brain activity that is not being inhibited by medication.

Drugs and alcohol can also alter EEG patterns, so EEG may be delayed until the effects of these substances wear off.

Interpreting Abnormal Results

The interpretation of an EEG study is very complex and requires specialized healthcare providers. Usually, an official EEG reading will not be available immediately because it takes time for a comprehensive review of the study.

Possible EEG results include:

• Evidence of seizure occurring during that study
• Localization of a seizure focus, which is one or more areas of the brain that could potentially predispose to seizures
• Interruptions in sleep correlating with low oxygen, indicative of obstructive sleep apnea or central sleep apnea
• Shortened sleep onset latency, which is indicative of sleep deprivation or narcolepsy
• Severe hypoxic brain injury, which can be reflected by certain patterns of altered brain activity on both sides of the brain
• Brain death, which can be reflected by an absence of consistent brain activity

Follow-Up and Next Steps

Your EEG results can help guide the next steps in your care. If you’ve been diagnosed with epilepsy, the EEG results may help to determine medication choices or in planning epilepsy surgery. Additionally, if your healthcare providers are trying to distinguish between a movement disorder, migraine, or epilepsy, your EEG results can help in your diagnosis.

When EEG is done as part of a polysomnogram, diagnosis of your specific sleep disorder will aid in pointing to the right treatment. For example, obstructive sleep apnea is often treated with lifestyle measures and devices that help to open the airways. Narcolepsy is treated with specific prescription medication.

If you or a loved one has had an EEG to assess changes in consciousness, the results can help determine prognosis and guide the discussion of how to proceed in light of the anticipated outcome.

Summary

An EEG is a noninvasive brainwave test that is used to evaluate and diagnose epilepsy, sleep disorders, and changes in consciousness. Sometimes EEG is necessary to help distinguish epilepsy from conditions that may have similar symptoms, such as movement disorders or migraine.

You may be instructed to prepare for your EEG by adjusting your medication or your sleep in the days before your test is scheduled. After your EEG, your healthcare providers will discuss the results and treatment plan with you.