Page created on June 3, 2021. Last updated on April 6, 2022 at 10:44
Definition and epidemiology
Epileptic seizures are single transient events caused by excessive or synchronous neuronal activity in the brain. There are many different types and many possible causes.
- Provoked seizures (topic 1B)
- Symptomatic seizures (topic 1B)
Most epileptic seizures are provoked or symptomatic in origin.
In 2017, the International League Against Epilepsy revised the classification of epileptic seizure types. This topic follows the new classification.
Epileptic seizures are classified as focal or generalised according to whether they originate from a circumscribed region of the brain, like a lobe or hemisphere, or from the entire brain.
- Focal seizures – those which originate from a circumscribed brain region
- Generalised seizures – those which originate from the entire brain
Focal seizures can be with or without awareness (previously called simple and complex partial seizure, respectively).
Seizures are also classified according to their clinical features (examples are given further down):
- Focal seizures
- Generalised seizures
- Non-motor (absence seizures)
Any seizure (focal or generalised) can progress into generalised tonic-clonic seizures.
Focal seizures with awareness (simple partial seizure)
Focal seizures may be with or without awareness. As a focal seizure, they originate from a circumscribed part of the brain or one hemisphere.
The exact features depend on the part of the brain involved. If the temporal lobe is involved, the patient may experience sensations in the stomach, olfactory hallucinations, or feelings of deja vu. Some other possible features are:
- Motor symptoms
- Automatisms (lip smacking, blinking)
- Sudden loss of tone in a muscle group (atonic seizure)
- Tonic contraction
- Jacksonian march – progressive involvement of different muscle groups as the seizure activity spreads along the motor cortex
- Nonmotor symptoms
- Autonomic symptoms (flushing, sweating)
- Behavioural arrest
- Sudden emotions (laughing, crying)
- Sensory symptoms (hallucinations, paraesthesia)
After the seizure, there may be residual transient neurological deficits depending on the affected region of the brain. This is called the postictal state. One special type of deficit is Todd paralysis, which is postictal weakness or paralysis.
Generalised seizures originate from both hemispheres and always involve impaired awareness. The most common generalised seizure is the tonic-clonic seizure, also called grand mal seizure. Any type of seizure can progress into this type. As the name suggests, there are two phases.
In the tonic phase there is generalised tonic muscle contraction, which usually causes extension of the limbs. The patient may form a “cry” as air is expelled out of their lungs. Due to tonic contraction of the respiratory muscles, there is apnoea which can lead to cyanosis. The tonic phase is followed by a clonic phase with generalised clonus (rhythmic muscle twitching), which eventually weans off.
During either of the phases, the patient may bite the lateral aspect of their tongue and have bladder incontinence.
Other common types of generalised seizures are:
- Motor seizures
- Myoclonic seizures – sudden myoclonus
- Clonic seizure – sudden clonus
- Tonic seizure – sudden muscle stiffening
- Atonic seizure – sudden loss of muscle tone
- Non-motor/Absence seizures – the patients motion or activity is interrupted by a blank stare and unresponsiveness. May occur hundreds of times a day. Lasts for seconds.
The postictal state following a tonic-clonic seizure involve unresponsiveness, amnesia of the event, aphasia, fatigue, hypersalivation, etc. Following a non-tonic-clonic generalised motor seizure there is no unresponsiveness or fatigue or other symptoms, but there may be amnesia of the event. Following generalised non-motor seizures, there is no postictal state.
The term epilepsy is used to describe a condition of predisposition to epileptic seizures, so that there is are recurrent epileptic seizures without provocation. This can be due to an epilepsy syndrome, or following the damaging effects of a stroke, tumour, trauma, etc.
Epilepsy syndromes are chronic conditions with typical clinical features, typical age of onset, typical types of seizures, and typical etiology. Some epilepsy syndromes include:
- Temporal lobe epilepsy
- Juvenile myoclonic epilepsy
- Childhood absence epilepsy
- Juvenile absence epilepsy
- West syndrome
Temporal lobe epilepsy
Temporal lobe epilepsy is the most common form of epilepsy, and it begins in childhood/adolescence. 50% of patients had febrile convulsions in childhood. There can be multiple causes, but the most common cause is sclerosis of the hippocampus (mesial hippocampal sclerosis).
It’s characterised by focal seizures with or without awareness and with features of seizures originating from the temporal lobe, most commonly sensations in the stomach, feelings of deja vu, and olfactory hallucations. However, any type of focal seizure may occur.
Video-EEG and neuroimaging are essential for the evaluation, as well as neuroimaging. Video-EEG refers to the use of video monitoring simultaneously as EEG, which allows us to examine both clinical features and EEG findings simultaneously. It may also be helpful to introduce provoking factors like sleep deprivation to provoke epileptic findings on the EEG.
If an EEG is made while a seizure occurs, epileptiform discharges can be seen. These spikes can also sometimes be present on the EEG between seizures, in which care they’re called interictal spikes. EEG findings can correspond to the affected area of the brain in case of focal seizures.
Unfortunately, a normal EEG does not exclude epilepsy and an abnormal EEG does not prove it. The diagnosis of epilepsy is mostly based on anamnesis.
70% of epileptic patients become seizure-free on chronic drug treatment. The type of drug depends on the type of epileptic seizure the patient has.
Focal epilepsy is treated with focal antiepileptic drugs, like carbamazepine, oxcarbazepine, and phenytoin.
Generalised epilepsy is treated with broad-spectrum antiepileptic drugs, like valproate, lamotrigine, levetiracetam.
If drug treatment is ineffective and the epilepsy is related to a specific location, we can perform epilepsy surgery. Most patients become seizure-free after surgery.
The last option for epilepsy is neuromodulation, either deep brain stimulation or vagus nerve stimulation.
Psychogenic non-epileptic seizures
This is not part of this or any other topic, but I think it’s something which is important to be aware of.
Psychogenic non-epileptic seizures (PNES) are seizures which resemble epileptic seizures, but which are not due to epileptic activity in the brain. They’re assumed to be psychogenic in origin, but a lot remain unknown regarding their pathogenesis. They’re involuntary responses to internal or external triggers, and so they are not under conscious control (in which case it would be malingering or facticious disorder). PNES are a type of conversion disorder (topic 29B).
Some argue for the use of the term dissociative seizures to be used instead of PNES, as the term “psychogenic” may be misleading (making the patient think that you think that it’s all in their head), and that “non-epileptic” is too vague. Dissociative seizures is also the term used in the ICD-10 (F44.5).
Patients with PNES often have comorbid psychiatric conditions. Many also have epilepsy (i.e., they have both epileptic seizures and PNES) and other functional neurological symptoms.
It’s important to distinguish PNES from epileptic seizures, as the management is different.
The etiology and pathophysiology of PNES is largely unknown, but there are some known risk factors, including:
- Early life trauma
- Dysfunctional social/family relationships
- Psychological stressors (poverty, abuse, job pressure, +++)
However, many patients have none of these risk factors.
Features which are typical for PNES include:
- Seizures resemble generalised tonic-clonic seizures
- Seizures occur in front of witnesses
- Seizures last longer than epileptic seizures (>5 minutes)
- Seizures never occur during sleep
- Eyes are closed during seizure
- Patient is conscious during the seizure
- No unusual features of epileptic seizures (deja vu, ictal tongue biting, mouth frothing)
- Usually no postictal state. Alertness and orientation return spontaneously
To a person who’ve seen generalised tonic-clonic seizures, distinguishing a witnessed PNES from a generalised tonic-clonic seizures is usually possible. Rather than following the typical tonic phase-clonic phase of epileptic seizures, PNES typically manifest with low frequency-high amplitude tremors rather than true clonus, as well as arching of the back and movement of the head from side to side.
However, clinical features can not clearly distinguish PNES from epileptic seizures, although they can suggest it.
Diagnosis and evaluation
The mainstay of distinguishing PNES from epileptic seizures is video-EEG. When no epileptiform waves are present on the EEG during a video-witnessed event, the diagnosis is most likely PNES.
See topic 29B.