Seizures: Pathology review

Definitions & Key takeaways

A seizure is a paroxysmal event due to abnormal electrical activity in the brain that can cause changes in behavior, consciousness, or movement. A seizure shouldn't be confused with epilepsy, which is said when two or more unprovoked seizures occur. Epilepsy is a chronic disorder that predisposes the individual to have recurrent seizures, and can't be diagnosed based on a single episode of seizures alone.

Seizures can be classified into generalized and focal seizures. Generalized seizures arise from both cerebral hemispheres at the same time, and almost always cause a sudden impairment of consciousness; whereas focal seizures arise from specific areas in one cerebral hemisphere, and present as a dysfunction of the part of the body controlled by the affected part of the brain.

When evaluating an individual with seizures, it's first important to identify the possible trigger. Diagnostic tests such as a CBC (complete blood count), electrolytes, liver function tests, and glucose levels, must be done to reveal potential causes. An EEG (electroencephalography) can also be done to assess the type of seizure. Treatment for seizures may involve supportive therapy, treating the underlying causes when possible, and antiseizure medications to manage convulsions.

Chapters:

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Case Study0:00–1:04

On the neurology ward, a 7-year old male, called Stefan, is brought by his mother. His mother is worried because he has several episodes every day where he loses consciousness for a few seconds.
His teacher also complains that she often catches him daydreaming during the lesson. Next to Stefan, there’s a 17-year old male, called Jacob, who seems sluggish and tired.
His friends brought him because he suddenly started “shaking and jerking” and he lost consciousness for about two minutes.
His medical history is otherwise insignificant. Now, there’s also an 11-year old female, called Megan, who also seems lethargic.
Her father is very upset because he witnessed an episode of twitching of her left foot that lasted a few minutes. Megan was unconscious and has no memory of the event.
Finally, there’s a 19-year old female, called Joanna, that has had repetitive episodes of sudden and rapid jerking movements with loss of consciousness for the past few months.
They usually occur when she wakes up in the morning and especially during periods of sleep deprivation. Okay, so all of them had a seizure episode.

Pathology1:04–2:06

A seizure is a paroxysmal motor, sensory or autonomic event that occurs due to abnormal, excessive and synchronous electrical discharges from neurons in the brain.
Seizures usually last less than 5 minutes. If it lasts more than 5 minutes, it’s called status epilepticus.
Epilepsy is a chronic disease of the brain that predisposes an individual to having recurrent unprovoked seizures; that is seizures without a clear triggering cause.
Epilepsy is typically diagnosed when an individual has two or more unprovoked seizures separated by at least twenty-four hours.
Okay, now seizures are broadly classified into two types, generalized and focal seizures. Generalized seizures arise from both cerebral hemispheres at the same time, while focal seizures arise from specific areas in one cerebral hemisphere.
However, focal seizures can spread to both cerebral hemispheres, causing a generalized seizure. When this happens, it’s appropriately called secondary generalization of a focal seizure.
Okay, now let’s take a closer look at the different subtypes of generalized seizures. Generalized seizures are subclassified into motor and non-motor seizures.

Generalized Seizure2:06–5:05

Regardless of the subtype, generalized seizures almost always cause a sudden impairment of consciousness. Generalized motor seizures include tonic, clonic, tonic-clonic, atonic, and myoclonic seizures.
Tonic seizures involve sudden stiffening of the muscles, while clonic seizures involve rhythmic twitching of the muscles.
However, these clinical features are usually combined, so individuals commonly have a tonic-clonic seizure. In a generalized tonic-clonic seizure, a person may have a sudden contraction of their vocal cord muscles, causing them to involuntarily scream or cry during a seizure.
Contraction of the ocular muscles can cause uprolling of the eyes. Contraction of the oropharyngeal muscles can impair swallowing, causing respiratory secretions to pool in the oropharynx.
Contraction of the jaw muscles may cause the individual to bite on their tongue. Individuals with tonic-clonic seizures may also develop urinary or fecal incontinence.
After the tonic-clonic seizure ends, individuals enter a period called the post-ictal phase, during which the individual’s consciousness is still impaired for minutes to hours, so they seem sluggish and tired or hard to wake up.
So on the exam, look for these subtle clues that indicate a post-ictal phase. Next are myoclonic seizures.
For the test, remember that myoclonic seizures involve sudden, rapid, muscle contractions. This sounds a lot like clonic seizures, but the key difference is that in myoclonic seizures, the contractions are much faster, occurring at a rate of 0.1 seconds, whereas in clonic seizures, the contractions occur at a rate of about 1 to 2 seconds.
Myoclonic seizures typically occur in the morning and are usually triggered by stress or sleep deprivation, and that’s something you also have to know for the exams!
Alright, now atonic seizures translates to “no muscle tone”. Therefore they are characterized by sudden loss of postural muscle tone lasting 1 to 2 seconds, causing the individual to collapse to the ground out of the blue.
Alright, moving on to the other arm of generalized seizures, there are the generalized non-motor seizures. These are called absence seizures and they are very high yield.
They are commonly found in children and adolescents. Episodes are characterized by sudden, brief loss of consciousness for seconds to minutes without any change in the individual’s muscle tone.
So, they could be sitting in class listening to a lecture and suddenly lose consciousness without falling down. Unfortunately, episodes can occur dozens or even hundreds of times per day, and are classically described by parents and teachers as “staring into space”, or “daydreaming”, or being “inattentive”.
In fact, many children with absence seizures are actually misdiagnosed with attention-deficit hyperactivity disorder, because teachers often presume that a child is just not paying attention.
Okay, now another high yield topic is focal seizures, previously called partial seizures. Focal seizures are classified into those that do not impair consciousness,, and those that impair consciousness.

Focal Seizure5:05–6:42

Focal seizures that impair consciousness are also followed by a post-ictal phase, whereas focal seizures that didn’t affect consciousness do not have a postictal phase.
Now, focal seizures can be motor, sensory, or autonomic, depending on the area of the cerebral cortex involved. For example, a focal seizure involving the primary motor cortex may cause tonic or clonic movements of the contralateral extremity, whereas a focal seizure involving the occipital cortex may cause someone to see flashing lights.
Sometimes, focal seizures may begin as subtle neurological symptoms called auras. During an aura, individuals may exhibit subtle muscle movements called automatisms, such as chewing, lip smacking, or rapid blinking of the eyes.
Other interesting forms of aura include smelling unusual odors like kerosene, a rising sensation in abdomen, or even feelings of fear or deja vu.
Also, an interesting phenomenon that occurs after focal motor seizures is Todd’s paralysis, which describes a temporary paralysis of the affected extremity.
Alright, now it might be difficult to know if a seizure was a generalized tonic-clonic right from the beginning, or if it was a focal seizure that secondarily generalized.
However, a history of an aura, unilateral shaking, turning of the head to one side or Todd’s paralysis is a clue it may have been a focal seizure that secondarily generalized.
Take that with a grain of salt though, because the absence of these historical features does not adequately exclude a focal seizure.

Febrile Seizure6:42–11:46

Okay, now a special subtype of seizures that occurs in young children between the ages of 6 months and 5 years are febrile seizures.
These only happen when the child develops a fever, and they can be generalized or focal. Because of this, febrile seizures are classified differently, and include simple and complex febrile seizures.
Simple febrile seizures are usually generalized, last less than 15 minutes, and do not happen again within 24 hours. Complex febrile seizures are usually focal in onset, last more than 15 minutes, and often happen more than once in the span of 24 hours.
For your exam, remember that infection with human herpes virus 6 or HHV-6 has a particularly high association with febrile seizures.
This virus also causes roseola infantum, a disease characterized by the development a high grade fever for about 3 to 5 days, then the fever goes away and a maculopapular rash appears on the trunk and spreads to the extremities.
So remember, fever first, rash later. Diagnostic investigations focus on looking for the cause of fever and excluding serious pathology.
For example, a lumbar puncture may be performed to exclude meningitis. Alright, now seizures are just a symptom, much like chest pain or shortness of breath, and therefore there are numerous causes of seizures.
We can categorize them based on the mnemonic “VITAMINS”. “V” stands for vascular, which includes ischemic or hemorrhagic strokes or intracerebral hemorrhage.
“I” is for infection, which includes meningitis, encephalitis or brain abscess. “T” is for trauma, especially penetrating traumatic brain injury, such as that from a gunshot.
“T” is also for toxins. This includes drugs of abuse such as cocaine or amphetamine overdose, or alcohol withdrawal, which typically develops 48 hours after the last drink.
Additionally, the anti-tuberculosis medication isoniazid can potentially cause seizures secondary to pyridoxine or vitamin B6 deficiency.
The antidepressant bupropion can also cause seizures, especially if given in individuals with eating disorders like anorexia or bulimia.
“A” is for autoimmune, such as central nervous system vasculitis or lupus. “M” is for metabolic, and this category includes a bellevue of electrolyte imbalances such as hyponatremia or hypocalcemia, or other metabolic imbalances such hypoglycemia or hyperglycemia, hyperthyroidism, hepatic encephalopathy in liver disease or uremic encephalopathy in kidney disease.
Also, Wernicke encephalopathy caused by thiamine deficiency should be considered, especially in alcoholic individuals. “I” is for idiopathic, which means epilepsy.
“N” is for neoplasm and “S” is for the differential diagnoses like psychogenic seizures or syncope. Also, one separate diagnosis that should be specifically considered in pregnant female is eclampsia.
This is when they have preeclampsia, which is high blood pressure during pregnancy with organ damage, and then develop seizures.
Okay, so when an individual presents with a history of a paroxysmal event, it’s important to first make sure the event was truly a seizure.
An important differential diagnosis of a seizure is syncope. Syncope is usually preceded by a prodrome of lightheadedness or sweating, followed by a brief loss of consciousness lasting seconds.
Similar to seizures, tonic or clonic movements can also be present in syncope. However, unlike seizures, syncope does not have a post-ictal phase, and individuals regain full consciousness a few seconds after the event.
Next is diagnosing seizures. The first step is to determine if the individual has had prior seizures, in which case they have epilepsy.
On the other hand, for a first-time seizure, it’s important to start by considering all potential causes. A diagnostic workup should include a complete blood count, or CBC, electrolytes, liver function tests, serum glucose levels, a toxicology screen, and in any woman of childbearing age, a pregnancy test.
An electrocardiogram or ECG can also be obtained if syncope is part of the differential. Brain imaging with CT or MRI is only done if a structural lesion is suspected or if no identifiable cause is found on laboratory evaluation.
If a brain infection like meningitis is suspected, a lumbar puncture can be obtained. If the workup doesn’t reveal an identifiable cause, then it’s considered an unprovoked seizure, and at this point we need to start thinking about epilepsy once again.
The next step is performing an electroencephalography, or EEG, which is done by placing electrodes on the scalp and monitoring the brain’s activity.
The EEG tells us whether the epilepsy is generalized or focal. Additionally, it can help with specific diagnoses.
For example, a 3-hertz spike and wave pattern on EEG is characteristic of absence seizures.Now, the treatment of seizures includes abortive therapy, which stops an ongoing seizure episode, and antiepileptic therapy, which prevents a future seizure from occurring.

Treatment11:46–12:31

Abortive medications are mainly used when the seizure has exceeded 5 minutes, in other words, status epilepticus. The main abortive medications are the benzodiazepines such as diazepam, midazolam and lorazepam.
As for antiepileptic medications, there are many options such valproic acid, phenytoin, phenobarbital and many others. A particularly high yield medication is ethosuximide, which is specifically used for absence seizures.
Also, in cases of eclampsia, the medication of choice is magnesium sulfate. Alright as a quick recap...
A seizure is a paroxysmal event that occurs due to abnormal and excessive electrical discharges in the brain. Epilepsy is a chronic disorder that predisposes the individual to recurrent seizures, and is typically diagnosed when either two or more unprovoked seizures occur.

Review12:31–13:27

Seizures can be classified into generalized and focal seizures. Generalized seizures include tonic, clonic, tonic-clonic, myoclonic, atonic and absence seizures.
Focal seizures include those that do not alter consciousness and those that do. Children are at risk of febrile seizures which can be classified as simple or complex.
When evaluating an individual with seizures, it’s first important to identify the possible trigger. Diagnostic tests such as a CBC, electrolytes, liver function tests and glucose levels, must be done to reveal potential causes.
An EEG can also be done to assess the type of seizure. Now, back to the patients!
Due to his age and history of episodes where he briefly loses consciousness and seems to be “daydreaming”, Stefan most likely has episodes of absences.

Summary13:27–14:10

Now, from his friends’ description of the event, Jacob had a generalised motor seizure, and most probably it was a tonic-clonic seizure.
Now, Megan had a focal seizure with loss of consciousness, or a partial complex seizure, since the seizure involved only her left foot.
Finally, Joanna most likely has episodes of myoclonic seizures which are typically rapid jerking movements that can be exacerbated by sleep deprivation.
Okay, now a diagnostic workup can be done for all of them in order to find a potential cause for the seizures. If the seizure is unprovoked, the individual may have epilepsy.
potential cause for the seizures If the seizure is unprovoked The individual might have epilepsy
Seizures: Pathology Review: Video and Causes | Osmosis