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Introduction

  • Abnormal slow activity: The most common EEG manifestation of focal brain dysfunction is abnormal slow activity, particularly polymorphic or arrhythmic delta (1-3 Hz) slowing.

  • Epileptiform abnormalities: These include spikes, spike-and-wave patterns, and sharp waves, which are common in epilepsy.

  • Non-epileptiform abnormalities: These can include generalized or focal slowing, triphasic waves, and periodic discharges.

  • Focal slowing: Indicates focal cerebral pathology and can be continuous or intermittent, often associated with structural abnormalities like tumors or strokes.

  • Generalized slowing: Indicates diffuse cerebral dysfunction and can be caused by various conditions such as metabolic encephalopathy, neurodegenerative disorders, or infections.

  • Interictal Epileptiform Discharges (IED): Abnormal synchronous electrical discharges generated by a group of neurons in the epileptic focus, including spikes and sharp waves.

  • Triphasic waves: High amplitude sharp waves with three phases, often seen in metabolic encephalopathies.

  • Burst suppression pattern: Characterized by brief bursts of electrographic activity in a background of isoelectric EEG, seen in severe brain injuries or induced by sedative drugs.

Epileptiform Abnormalities [1]

  • Spikes: Very short in duration with a sharp-pointed peak, typically lasting 20 to 70 milliseconds.

  • Spike-and-wave: A spike followed by a wave component, common in absence seizures.

  • Sharps: Longer in duration than spikes, lasting 70 to 200 milliseconds.

  • Polyspike-and-wave: Repetitive spikes followed by a wave, seen in generalized epilepsy.

  • Generalized spike-and-wave: Single spike followed by a wave, seen in primary generalized epilepsy.

  • Centro-temporal spikes: Seen in benign focal epilepsy of childhood, characterized by horizontal dipoles.

  • Slow spike-and-wave: Bilaterally synchronous discharges, typical in Lennox-Gastaut syndrome.

  • Lateralized periodic discharges (LPDs): Repetitive focal discharges at regular intervals, often seen with focal structural lesions.

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Non-Epileptiform Abnormalities [1]

  • Slowing: Indicates cerebral dysfunction, can be polymorphic or rhythmic.

  • Diffuse slowing: Indicates global cerebral dysfunction, can be caused by sedative medications, metabolic encephalopathy, or infections.

  • Focal slowing: Indicates focal cerebral dysfunction, can be continuous or intermittent.

  • Triphasic waves: High amplitude sharp waves with three phases, seen in metabolic encephalopathies.

  • Burst suppression pattern: Brief bursts of electrographic activity in a background of isoelectric EEG, seen in severe brain injuries or induced by sedative drugs.

  • Electrocerebral inactivity (ECI): No detectable EEG activity, used as a supportive test in the diagnosis of brain death.

  • Breach rhythm: Focal abnormal morphology and change in voltage seen over areas of cranial or scalp defects.

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Focal Slowing [2]

  • Indicates focal cerebral pathology of the underlying brain region.

  • Can be intermittent or persistent, with more persistent slowing indicating more severe dysfunction.

  • Common causes include stroke, brain hemorrhage, tumors, traumatic injury, and infections.

  • Intermittent focal slowing may indicate subtle focal cerebral dysfunction due to sedative medications.

  • Continuous focal slowing is often indicative of structural abnormalities like brain tumors or strokes.

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Generalized Slowing [2]

  • Indicates diffuse cerebral dysfunction.

  • Can be caused by sedative medications, neurodegenerative disorders, metabolic or toxic encephalopathy, and infections.

  • Generalized background slowing in the theta and delta frequency ranges is normal in children and during sleep.

  • Persistent, unvarying, and unreactive generalized slow wave activity in a vigilant adult is considered pathologic.

  • Examples include metabolic encephalopathy, neurodegenerative disorders, and CNS infections.

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Clinical Significance [1]

  • A normal EEG does not rule out epilepsy, as the sensitivity of an EEG to identify epilepsy is less than 50%.

  • Healthy volunteers may have interictal discharges and other EEG abnormalities.

  • Unneeded EEG testing can lead to unnecessary and erroneous diagnoses.

  • Abnormalities noted on the EEG must always be clinically correlated.

  • An interprofessional team approach involving EEG technicians, nurses, and physicians provides the best care for patients with abnormal EEGs.

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EEG Test Procedure [3]

  • The test is done by an EEG technologist in a healthcare provider's office, hospital, or laboratory.

  • Electrodes are placed on the scalp and connected to a recording machine.

  • The patient needs to lie still during the test with eyes closed.

  • The test may involve breathing fast and deeply or looking at a bright flashing light.

  • An ambulatory EEG may be ordered for longer monitoring, where the patient wears a special recorder for up to 3 days.

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Related Videos

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