Seizures

Madona Plueger

Keywords: epilepsy, epilepsy monitoring unit, partial seizures, primary generalized seizures, psychogenic nonepileptic seizures, seizure semiology, status epilepticus

6.1 Seizures

A seizure is a single, temporary event that occurs when uncontrolled electrical neuronal discharges of the brain interrupt normal brain function. Seizures are a relatively common occurrence associated with most neurologic disorders, including tumors, trauma, and infectious processes such as meningitis. They may also occur with nonneurologic disorders, such as dehydration and other metabolic problems. Seizures can occur at any age, but they are most common in children and in people older than 60 years. The prevalence of seizures in the developed world is 0.5 to 1% (Box 6.1 Conditions Associated with Seizures).

In patients with epilepsy, seizures are spontaneous and may recur. Epilepsy may be idiopathic, or it can result from an underlying condition. It is one of the most common disorders of the central nervous system, affecting almost 2.9 million people in the United States alone. In 2010, the International League Against Epilepsy categorized epilepsy as a “disease.” Individuals with epilepsy commonly face obstacles to appropriate health care, and epilepsy is often misunderstood by the public, which gives rise to stigma directed at persons with the condition.

6.2 Types of Seizures

There are many different types of seizures, and a person who has epilepsy can have more than one type. Epilepsy is classified not only by seizure type (▶ Table 6.1) but also by other important distinguishing characteristics. These characteristics may include the following:

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  Precipitating factors of the seizure

  
  
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  Clinical features (e.g., behavior and type of movement)

  
  
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  Abnormal brain wave recordings (e.g., spikes and sharp waves)

  
  
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  Genetic features

  
  
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  Expected course of the disorder

  
  
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  Expected response to the treatment.

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  Table 6.1 Types of epilepsy

  Type	Partiala	Features	Generalizeda	Features
  Idiopathic (genetic)	Benign focal epilepsy of childhood	Seizures are infrequent and usually nocturnal; usually only span 1–3 y after onset	Childhood absence epilepsy (also called pyknolepsy)	Seizures occur several times a day; girls are more frequently affected than boys
  			Juvenile myoclonic epilepsy (also called Janz’s syndrome)	Occurs in the morning or in cases of stress or fatigue No associated mental decline
  			Epilepsy with seizures that occur on awakening	Grand mal seizures
  Symptomatic (known cause)	Temporal lobe epilepsy	Accounts for 60% of all epilepsy cases; auras are common	West’s syndrome	Infantile spasms
  	Frontal lobe epilepsy	Brief recurring seizures that often occur while the patient is asleep	Lennox–Gastaut syndrome	Atypical absence epilepsy
  Cryptogenic (unknown cause)
  aThese lists are not definitive and include only the most common types of epilepsy.

6.2.1 Generalized Seizure

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  The only type of seizure seen in idiopathic generalized epilepsy

  
  
  
  
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    Has a genetic component

    
    
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    Affects a younger population

    
    
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    Affects both cerebral hemispheres

    
    
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    Results in loss of consciousness

    
    
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    Symptoms include

    
    
    
    
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      Blank stare

      
      
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      Falling to the floor

      
      
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      Sudden muscle jerking

      
      
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      Repetitive stiffening and relaxing of muscles

Secondarily generalized seizures, which are partial seizures that include loss of consciousness, are particularly common.

6.2.2 Partial Seizure

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  Affects a specific area of one cerebral hemisphere

  
  
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  May evolve into prolonged seizures

  
  
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  Results from structural disruption in a specific part of the brain (type of symptoms indicate which area of the brain is affected)

  
  
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  May evolve into a condition called status epilepticus, or repeated (i.e., continuous) epileptic seizures, in which the patient does not regain consciousness between episodes

Simple Partial Seizure

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  This brief sensation of abnormality is also called an aura; it can, but does not necessarily, progress to a more serious seizure

  
  
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  Does not result in loss of consciousness

  
  
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  Depending on the part of the brain in which the seizure originates, simple partial seizures may include

  
  
  
  
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    Motor symptoms (e.g., muscle stiffening or jerking on one or both sides of the body)

    
    
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    Visual, auditory, olfactory, and gustatory abnormalities

    
    
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    Vertiginous sensation

    
    
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    Effects of autonomic involvement (e.g., pallor, sweating, flushing, pupil dilation, and abnormal epigastric sensation)

Complex Partial Seizure

A complex partial seizure usually starts in the temporal or frontal lobe of the brain before spreading to other areas of the brain. It may begin with motor impairment and typically culminates in impaired awareness. This type of seizure may be preceded by an aura. Common characteristics include

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  Loss of consciousness and several minutes of unresponsiveness

  
  
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  Blank stare and impaired awareness (e.g., confusion and unfocused mental state)

  
  
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  Unusual sensations (e.g., memory flashbacks, depersonalization of surroundings, a reported “out-of-body” experience, visual or auditory distortions, and strong emotional responses, such as rage, terror, elation, and sadness)

  
  
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  Automatisms (e.g., smacking of lips, chewing, picking up objects, walking aimlessly, disrobing in public, and repeating words and phrases)

  
  
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  Poor safety awareness (e.g., unaware of the dangers of traffic, fire, or heights)

The period of time after a seizure is referred to as the postictal period. After a complex partial seizure, the patient may experience confusion and may not even remember the event.

Psychogenic Nonepileptic Seizure

A psychogenic nonepileptic seizure is an involuntary seizure triggered by stress that often occurs without evidence of psychopathology. In other words, the patient may show signs of having had a seizure, but there is no evidence of abnormal activity in the brain. Sometimes, it is referred to as a pseudoseizure, but this term should be avoided because it implies that the seizure is feigned and the patient is malingering for secondary gain. Psychogenic nonepileptic seizures may mask actual undiagnosed disorders, such as

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  Anxiety disorders

  
  
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  Posttraumatic stress disorder

  
  
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  Conversion disorder

  
  
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  Psychosis

  
  
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  Somatization disorders

  
  
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  Reinforced behavior patterns (in cognitively impaired patients)

Nonepileptic Seizures of Physiologic Origin

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  Metabolic abnormalities

  
  
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  Cardiac dysfunction

  
  
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  Movement disorders

  
  
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  Migraines

  
  
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  Side effects of drugs

Seizure Semiology

Seizure semiology is a way to describe the clinical manifestations (i.e., symptoms) of a seizure. It can help the care team understand more about the seizure by determining the location of its focus, that is, the area of the brain from which the seizure originated (▶ Fig. 6.1 and ▶ Table 6.2).

6.2.3 Diagnosing Epilepsy

History

A thorough history of the patient’s past experience with seizures is critical to help diagnose epilepsy (Box 6.2 International League Against Epilepsy 2014 Diagnostic Criteria). This history should include

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  Types of seizures

  
  
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  Frequency of seizures

  
  
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  Age of patient at first seizure

  
  
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  Family history of seizures

  
  
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  Precipitating events

  
  
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  Antiepileptic drug (AED) usage

Imaging Studies and Noninvasive Diagnostic Tests

The imaging studies and noninvasive diagnostic tests described in the following sections can help physicians determine the type and focus of seizures that the patient is having, so that they can diagnose or rule out epilepsy (▶ Table 6.3).

Imaging Studies

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  Magnetic resonance imaging (MRI)

  
  
  
  
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    Identifies structural lesions or areas of sclerosis to locate seizure focus

  
  
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  Positron emission tomography scan

  
  
  
  
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    Identifies areas of hypometabolism to identify seizure focus

  
  
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  Ictal single-photon emission computed tomography

  
  
  
  
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    Radioactive tracer injected intravenously (IV) during a seizure helps locate the focus of the seizure by tracking blood flow in the brain

Other Diagnostic Tests

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  Electroencephalogram (EEG)

  
  
  
  
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    Noninvasive; records 20 minutes of brain wave activity (▶ Table 6.4)

    
    
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    Lateralization (determining whether the seizure originates from the left or the right hemisphere) and localization (identifying the focus within a specific region of one hemisphere) begin with standard scalp EEG recordings

    
    
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    The presence of interictal (between seizures) epileptiform discharges (sharp waves or spikes) in a single location is highly suggestive of the onset of seizure in that region

    
    
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    Ictal scalp EEGs during complex partial or secondarily generalized seizures usually show a lateralized rhythmic discharge that increases in frequency and amplitude as it spreads to the postictal stage and that varies in location

    
    
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    Two forms of provocative tests are used during a standard EEG

    
    
    
    
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      Hyperventilation: In this test, patients are asked to hyperventilate for 3 to 5 minutes; this lowers the level of intracerebral carbon dioxide and elicits epileptic and other abnormal neuronal activity

      
      
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      Photic stimulation: In this test, a strobe light is used to trigger a convulsion; the light elicits epileptic activity in 5% of patients with epilepsy

    
    
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    The EEG may not capture seizure activity, unless it is being recorded during the seizure

    
    
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    Simple partial seizures, including auras, often do not appear on scalp EEG studies

  
  
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  EEG–video monitoring

  
  
  
  
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    Cornerstone of epilepsy surgery evaluation; involves continuous EEG with concurrent video camera monitoring to observe the patient’s behavior when the seizures occur

    
    
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    Patients undergoing this type of testing are transferred to an epilepsy monitoring unit (EMU) until they have a typical seizure spell

    
    
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    AEDs are often withheld to elicit spells more quickly

    
    
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    EEG–video monitoring can confirm whether the patient’s spells are in fact epileptic

    
    
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    Roughly 25% of patients who are referred to an EMU for an epilepsy presurgical evaluation do not have epileptic seizures (most have psychogenic nonepileptic seizures)

  
  
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  Wada test

  
  
  
  
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    Helps establish which hemisphere houses language and memory centers

    
    
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    During this test, the conscious patient undergoes a cerebral angiogram after unilateral injection of amybarbital into the internal carotid artery; amybarbital anesthetizes the entire contralateral hemisphere of the brain

    
    
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    The patient is asked to remember various words

    
    
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    Language is tested by recording the patient’s ability to speak after injection (the patient is unable to speak or understand language when the language-dominant hemisphere has been anesthetized)

    
    
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    Memory is tested by asking the patient to recall the words after the effect of the anesthetic wears off.

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    Table 6.4 Brain waves seen on electroencephalogram

    Wave type	Hertz range	Location	Normal	Pathologic
    Delta	0–4 Hz	Frontal lobe	Slow-wave sleep in adults	Diffuse lesions Metabolic encephalopathy Hydrocephalus
    Theta	4–7 Hz	Both sides symmetrical if normal or focal if abnormal	Normal drowsiness	Posterior dominant rhythm in awake adult Metabolic encephalopathy or deep midline disorders
    Alpha	7–14 Hz	Posterior region of head on both sides; amplitude is higher on dominant side	Relaxed or reflecting, closing the eyes	Coma
    Beta	15–30 Hz	Both sides, symmetrical distribution, most evident frontally; low-amplitude waves	Alert or working Active, busy, or anxious thinking and active concentration	Absent in patients with cortical damage Benzodiazepine use
    Abbreviation: Hz, hertz.

Invasive Diagnostic Procedures and Invasive Monitoring

Patients for whom medical treatment has failed are usually candidates for epilepsy surgery. For these procedures, as described in the following sections, electrodes are placed directly on or in the brain during a presurgical evaluation to ensure accurate localization of the seizure focus. The two most common types of electrodes are depth electrodes and subdural electrodes.

Depth Electrodes

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  A cable with cylindrical contacts along its distal end, primarily used in cases of suspected medial temporal lobe epilepsy

  
  
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  Placed in hippocampus and amygdala for medial temporal lobe epilepsy; see also Chapter 1: Anatomy

  
  
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  Stereotactically placed through burr holes in the skull; see also Chapter 15: Neurosurgical Interventions

  
  
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  May be used in combination with subdural strip electrodes, described in the following section

Subdural Electrodes

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  A platinum or stainless steel disk embedded in a thin plastic cover

  
  
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  Can be used to record the area of seizure onset and to perform extraoperative stimulation mapping of cortical function in underlying brain tissue

  
  
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  Records activity from the surface of the brain

  
  
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  Most commonly used in neocortical epilepsy or suspected medial temporal lobe epilepsy to delineate the region of seizure onset (▶ Fig. 6.2 and ▶ Fig. 6.3)

  
  
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  Requires a craniotomy for placement.

  
  
  
  

  

  
  

  Fig. 6.2 Axial computed tomogram showing subdural electrodes.

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