Seizures & Epilepsy - Overview
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Seizures & Epilepsy
Key Definitions
Seizure
- A seizure is an acute, transient neurological event (typically less than 5 minutes in duration) caused¬ by abnormal (excessive or synchronous) electrical discharges within the brain.
Epilepsy
- Epilepsy is the syndrome of recurrent, unprovoked seizures.
- Provoked seizures can occur from conditions like intracranial hemorrhage or metabolic causes; unprovoked seizures do not have a triggering cause.
Status Epilepticus
- Status epilepticus refers to seizure activity that fails to terminate within the anticipated time period (variably defined as anywhere from 5 – 30 minutes) OR it refers to a series of consecutive seizures without intervening recovery.
- Status epilepticus has a mortality of 15 – 20%; however, it is the underlying etiology for the seizures that is the major contributor to this poor prognosis.
- Thus, as clinicians, we should never "give-up" on a patient no matter how long the duration of the status epilepticus, as the seizures can persist for weeks and patients can still have a good outcome if the underlying etiology resolves or is treated.
Key Epidemiology
Seizure Prevalence
- 5 to 10% of people will have a seizure at some point in their life; most often in early childhood or late adulthood.
- Not everyone who has a seizure will have a violent, convulsive event, however. As we'll learn, however, seizure semiology is broad and varied: they can manifest as something small and focal, such as a strange feeling or visual illusion of flashing lights or something big and generalized, such as violent stiffening and shaking activity with a loss of consciousness.
Epilepsy Prevalence
- 1 to 4% of people have epilepsy; different organizations and societies provide widely varying estimates.
- The World Health Organization (WHO) and Centers for Disease Control (CDC) an epilepsy prevalence of ~ 1% whereas the American Epilepsy Society reports a figure of ~ 4%.
Common Causes of Provoked Seizures
- Stroke
- Brain tumor
- Brain injury
- CNS infection
Most Common Cause of Epilepsy, Worldwide
- Neurocysticercosis (taenia solium) is the most common cause of epilepsy, worldwide.
- The seizures come from the accumulation of cysts within the brain, which occurs when patients swallow the eggs found in the feces of a person who has an intestinal tapeworm.
Seizure Categorization
Onset Pattern
Focal (aka Partial)
- Focal (aka partial) onset seizures originate from networks within one hemisphere (typically in a discrete region).
Generalized
- Generalized onset seizures originate from networks that involve both hemispheres.
Focal to Generalized (aka Secondarily Generalized)
- If a seizure begins in one hemisphere and subsequently involves both hemispheres, we call this a focal to bilateral seizure (aka secondarily generalized seizure).
Focal
- In focal onset seizures, awareness (ie, consciousness) can be impaired (aka complex partial seizures) or preserved (aka simple partial seizures).
- Note, that in generalized seizures, by definition, awareness is almost always impaired.
- Clinically, focal seizures can have either motor or non-motor features.
Generalized
- Motor & Non-Motor seizures.
- Major types of motor seizures:
- Tonic-clonic
- Myoclonic
- Atonic
- Major non-motor seizure type:
- Absence
Generalized Seizures
Tonic-Clonic
- Most prominent generalized, motor seizure
Semiology
- Tonic phase = stiffening; Clonic phase = rhythmic jerking.
Mimicker
- A key mimicker of tonic-clonic seizure is convulsive syncope, which are convulsions brought on by syncope, a loss of adequate cerebral perfusion, rather than by abnormal electrical activity in the brain.
- Bear in mind that one of the most common mimickers of generalized seizures, and most seizure types, is actually non-epileptic spells (aka psychogenic seizures).
Syndromes
- Generalized tonic-clonic seizures can occur in a wide-variety of epilepsy syndromes.
Detailed Semiology
Pre-ictal
- Often a pre-ictal sensory prodrome that can last minutes to hours.
- The ictal phase refers to the seizure, itself: the event.
Tonic Phase
- Tnic stiffening: the back and neck are arched. The patient is lying down because there is a loss of consciousness.
Clonic Phase
- Characterized by rhythmic jerking (convulsions) of the face, arms, and legs.
Apnea
- During the ictal phase, there is often apnea with frothing at the mouth, choking sounds, and cyanosis (a blue appearance to the skin), which can mimic a cardiac arrest.
Post-ictal Relaxation
- After the event, post-ictal, there is post-ictal relaxation, which involves a stupor with possible bladder or bowel incontinence and deep, slow respirations.
EEG Correlation
- See: Tonic-Clonic Seizure
- For reference, the region between the vertical lines is one second.
- The number of wave cycles within that one second is the frequency, which is measured in Hertz (Hz).
- A single wave cycle in one second would be 1 Hz.
Tonic Phase
- At the initiation of the seizure, during the tonic phase, the EEG rhythm is a 10 Hz tonic (fast frequency), low amplitude waveform.
Clonic Phase
- During the clonic phase, the corresponding EEG rhythm is 4 Hz (slower frequency) spike-and-wave activity.
Post-ictal Slowing
- After the event, there is post-ictal slowing, with only a few wave cycles per second.
Myoclonic - juvenile myoclonic epilepsy (JME)
- Myoclonic seizures, manifest with brief, shock-like muscle jerks.
Mimicker
- Often mistaken for a movement disorder.
Epilepsy
- Myoclonic seizures are an important component of juvenile myoclonic epilepsy (JME), which begins in adolescence (12 – 18 years old).
- It is one of the photosensitive epilepsies; seizures can be triggered by flashing or flickering lights.
Detailed Semiology
- In juvenile, myoclonic epilepsy events characteristically cluster upon awakening in the morning.
- Jerks are described as "lightning-like".
- They manifest with symmetric, irregular, shock-like, jerks of the shoulders and arms, most notably, which can cause the person to drop items, but can also affect the legs, which can cause falls.
EEG Correlation
- EEG demonstrates polyspikes, which correlate with the myoclonic jerks, and characteristic disorganized, 4 – 5 Hz polyspike and wave discharges.
- See: Polyspike-and-Wave Complexes
- See: Status Myoclonus
- As mentioned, these discharges have a strong photoparoxysmal response, so flashing lights are used during EEG to elicit these discharges.
Atonic - Lennox-Gastaut
- Atonic seizures cause as loss of tone (drop attacks).
- Manifest with brief loss of muscle tone in the postural muscles or head.
Mimicker
- Can be hard to distinguish from syncope, which also involves a sudden loss of tone.
Epilepsy
- An important feature of Lennox-Gastaut syndrome, which involves multiple seizure types, including atonic seizures and cognitive dysfunction. It peaks at ~ 4 years of age.
EEG Correlate
- Slow (1.5 – 2 Hz ) spike-and-wave discharges.
Absence - childhood absence epilepsy (CAE)
- Absence seizures (aka petit mal seizures) manifest with a blank stare; patients appear to be daydreaming or zoning out.
- These patients may exhibit rhythmic facial movements or motor automatisms.
- Notably, there is no postictal confusion; patients can pick right back up where they left off with an activity.
Mimicker
- It is essential to distinguish absence seizures from an attentional disorder, as these patients can be mistakenly diagnosed with a learning disability.
Epilepsy
- They are the major seizure manifestation in childhood absence epilepsy (CAE), which typically occurs between 4 to 8 years of age, affects girls more than boys, and can involve 100s of seizures in a day.
- Children with absence seizure appear to be "daydreaming" or "staring off" in school.
EEG Correlation
- The EEG demonstrates runs of well-organized 3 Hz generalized high-voltage rhythmic spike-and-wave discharges.
juvenile absence epilepsy (JAE)
- For reference, juvenile absence epilepsy (JAE) is another generalized epilepsy syndrome, which we can think of (albeit a simplification) as a mixture of childhood absence epilepsy and juvenile myoclonic epilepsy:
- it occurs at 9 – 13 years of age
- it involves absence and myoclonic seizures that tend to occur shortly after awakening.
Focal Seizures
Overview
- The primary focal epilepsy syndrome is temporal lobe epilepsy, which is why in our diagram we show the seizure emanating from the medial temporal lobe, but focal seizures can occur from any cerebral lobe.
- To localize the origination of the seizure, we can use both lateralizing and localizing signs.
- On EEG, we look for focal epileptiform discharges.
Lateralizing Signs
Versive Movements
- Contralateral turn of the head and/or eyes (away from the seizure).
Todd's Paralysis
- A post-ictal weakness in the side of the body opposite to the seizure.
- Consider the post-itcal slowing: the brain is slow and suppressed, so naturally the corresponding side of the body is limp and weak.
Stroke Mimickers
- Naturally, then, these signs can be important mimickers of stroke. In stroke:
- The eyes can drift toward the side of the stroke: they look at the healthy side of the body (this is the opposite direction from in seizure wherein they look away from the seizure).
- There is weakness on the side opposite of the stroke, similar to a Todd's paralysis.
Additional Signs
Some commonly discussed, albeit less reliable lateralizing signs, include the:
- Figure 4 Sign
- The arm contralateral to the seizure is extended at the elbow with the wrist in flexion and the fist is clenched.
- The ipsilateral limb is in elbow flexion.
- Fencing Posture
- The arm contralateral to the seizure is raised and semi-extended above the head, as if holding a fencing foil.
- The head is turned toward the raised arm while the ipsilateral arm is semi-flexed at at the patient's side.
Localization
- The most common locality for focal seizures is the medial temporal lobe.
Temporal Lobe
- Seizures often manifest with sensory auras, automatisms, or speech arrest (or another form of cognitive impairment).
- Epigastric rising
- Inappropriate fear
- Olfactory hallucinations
- Deja Vu
- Wide variety of sympathomimetic, gastrointestinal, and respiratory symptoms
Frontal Lobe
- Frontal lobe seizures tend to be stereotyped and nocturnal. They are easily confused for psychogenic seizures or a movement disorder (especially because there is often NO loss of awareness or postictal phase).
- Manifestations of frontal lobe seizures range from emotionally-driven, fearful hallucinations to motor activity: tonic-clonic movements and the more complicated positions described previously (figure 4 sign, fencing posturing, etc…).
Parietal Lobe
- Parietal lobe seizures tend to cause somatosensory auras, which we could predict given the role of the parietal lobe in sensory processing.
- Note, however, that parietal lobe seizures are notoriously poorly localizing and they will commonly propagate to more regions with more readily obvious manifestations, such as the frontal lobe or the occipital lobe, before they are recognized.
Occipital Lobe
- Occipital lobe seizures often produce elemental visual phenomena, such as flashing lights or geometric shapes, much like migraine auras.
Insular Cortex
- Characteristically manifest with symptoms involve the GI system and throat, such as vomiting, hypersalivation, dysarthria or strange thoracoabdominal sensations.
Nomenclature
2017 ILAE (International League Against Epilepsy) classification system
Seizure Description
Although the following terms are still widely used, the 2017 ILAE classification system has made the following updates:
- Partial seizures referred to focal seizures
- Complex partial seizures referred to seizures of focal onset that resulted in loss of awareness.
- Simple partial seizures referred to focal seizures with NO loss of awareness.
- Secondarily generalized seizures referred to seizures of focal onset that ultimately generalized; these are now called focal to bilateral tonic-clonic seizures.
Epilepsy Syndromes
Although, we still widely use the term "idiopathic generalized epilepsies," but the 2017 nomenclature now employs the term "genetic epilepsies" (akin to "genetic myopathies", which we discuss in the neuromuscular disorders section). Importantly, genetic epilepsies do NOT have to be inherited, they can occur due to de novo mutations.
- As well, they do NOT require genetic testing to make a diagnosis of genetic epilepsy, especially since the genetic mutation is often assumed and not yet known.
For more information on this subject, see: Epilepsy Nomenclature