Evidence-Based Reviews

EEGs and epilepsy: When seizures mimic psychiatric illness

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If a patient with psychiatric illness has seizure-like episodes, an abnormal EEG may help confirm the diagnosis. This neurologist offers five case studies as a quick primer for making the most of EEGs.


 

References

Behaviors during seizures can mimic psychiatric disorders, and patients with epilepsy have higher-than-normal rates of many types of psychiatric illness. That’s why it is important for psychiatrists to be familiar with epilepsy and electroencephalography (EEG)—the key diagnostic tool for epileptic disorders.

As a neurologist who specializes in epilepsy treatment, I offer five case studies that highlight basic concepts about epilepsy and EEGs. My goal is to help psychiatrists answer common clinical questions such as:

  • If a patient with bipolar illness has an abnormal EEG, should this guide the treatment choice?
  • In a patient with episodes of fear, tachycardia, and other autonomic symptoms, how does one differentiate between panic attacks, complex partial seizures, and psychogenic nonepileptic seizures?
  • When is EEG indicated in a patient with attention-deficit/hyperactivity disorder (ADHD)?
  • Can complex partial status epilepticus present as a psychiatric disorder?
  • In patients with epilepsy, why is it important to categorize psychiatric symptoms as ictal (occurring at the time of seizure), interictal (between seizures), or postictal (following seizures)?

How EEG is used today

EEG is used mainly to evaluate epilepsy and diffuse brain dysfunction (e.g., coma and confusional states). Modern brain imaging, including magnetic resonance imaging (MRI) and computerized tomography (CT), has replaced EEG for evaluating structural brain abnormalities.

Two basic EEG findings with which psychiatrists should be familiar are slowing and epileptiform activity:

Slowing is a nonspecific finding that indicates dysfunction of the underlying white matter, with or without gray matter involvement. Focal slowing indicates a focal area of cortical dysfunction usually caused by a focal structural lesion (tumor, stroke, trauma, etc.), although a lesion is not always found. Brain imaging, usually MRI, is indicated.

Epileptiform activity, which is seen as spikes or sharp waves, indicates potential for epileptic seizures (Box). EEG technologists may use activation procedures such as hyperventilation and photic stimulation to enhance the ability of EEG to detect epileptiform activity. Special electrodes (e.g., anterior temporal electrodes) may be used to improve recordings taken from the temporal lobe. In selected inpatients, epilepsy centers may use sphenoidal electrodes—wires inserted under the skin of the cheek to record temporal lobe activity.

Video/EEG monitoring has been used since the 1960s and is the gold standard in evaluating patients with seizures or episodes that resemble seizures. The technique involves simultaneously recording brain activity on an EEG and behavior on tape or digital video. Usually patients are admitted to a specialized hospital unit, medications are reduced or discontinued, and the seizures or other behaviors are recorded. Neurologists with special training in EEG and epilepsy evaluate the EEG for changes before, during, and after the behavioral event. Clinical characteristics of seizures and nonepileptic events detected on the video also help with the evaluation.

Video/EEG is most helpful in:

  • determining whether the events are epileptic or nonepileptic
  • determining—if epileptic—the precise seizure type for treatment decisions
  • localizing the site of seizure onset in patients with medication-resistant epilepsy who may be candidates for epilepsy surgery

Normal variants occur frequently on EEG and may be misinterpreted because they resemble epileptiform activity. They include:

  • benign epileptiform transients of sleep
  • mu rhythm
  • rhythmic midtemporal variant
  • subclinical rhythmic epileptiform discharge in adults.

Experienced electroencephalographers can readily identify these normal variants, but some neurologists may misidentify or misinterpret these EEG findings, potentially leading to unnecessary treatment with antiepileptic drugs.

Hundreds of medications can alter an EEG, usually by increasing either slowing or beta activity. The most common change is excessive beta activity, which is seen in most patients taking benzodiazepines or barbiturates. Enhanced beta activity is an appropriate response of a normal brain to certain medications and does not indicate underlying brain pathology.

If a patient with psychiatric illness has seizure-like episodes, an abnormal EEG may help in diagnosis. A neurologist can help direct the patient evaluation. Whether or not interictal EEG abnormalities are present, video/EEG monitoring can often make the diagnosis by capturing the events.

Case 1: Does this patient have epilepsy?

For Mr. A, age 27, lithium has stabilized his bipolar I disorder for 2 years without significant adverse effects. An EEG ordered for unknown reasons by his primary care physician shows large amounts of beta activity and a single sharp wave from the right temporal region. Should you add an antiepileptic drug to his regimen?

In this patient, lithium probably caused the large amounts of beta activity. A rule of thumb says that if an EEG shows increased beta activity, a medication is almost certainly the cause. If an EEG finds increased generalized slowing, medication effect is one of many possible causes.

The single sharp wave from the right temporal lobe raises the possibility of increased susceptibility to seizures but is not diagnostic of epilepsy. There is no indication to change the patient’s treatment regimen if he is well controlled without adverse effects from his current medications and there is no clear history of clinical seizures. In short, treat the patient, not the EEG.

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