Epilepsy Flashcards
What is an epileptic seizure?
A transient( passes with time, is brief and short lived) uncontrolled discharge of cerebral neurones causing a variety of symptoms, usually associated with a disturbance of consciousness.
The firing of the neurones is disordered, and can cause convulsions and involuntary skeletal muscle contractions.
Sometimes this may be preceded by an aura, such as tingling, numbness or hallucinations.
After the seizure has passed there may be a period of drowsiness, headache or confusion.
Why does epilepsy occur?
70% of epilepsy cases have known causes.
The other 30% have causes including: Head trauma Poisoning Infection Maternal injury Brain tumour Cardiovascular problems affecting blood supply
What is epilepsy?
Epilepsy is a term used to described when more than one seizures recur.
How many different types of epilepsy, and why is important to know what type a patient suffers from?
There are more than 40 types of epilepsy.
It is important to know high type of epilepsy a patient suffers from, as there are different treatments for different types of epilepsy, and a drug which may help on type could make other types worse.
The seizures can be generalised into two types.
Partial and generalised.
What is partial or focal seizures?
This occurs in a small, specific part of the brain and symptoms are recognisable as originating from that part of the brain.
For example, in a motor area, you would see motor symptoms, if it was from the area responsible for colour vision, there may be distortion of colours etc.
What are generalised seizures?
This affects both hemispheres of the brain, not just one small area, and tends to be the type which cause more serious symptoms.
How is epilepsy diagnosed?
Detailed history taken, often from bystanders as sufferers will often not remember anything that happen during the seizure.
There are lab test such as ECG and EEG that can examine the brain to try and support diagnosis. MRI scan, examine structure and and changes. They only help with history, not useful individual.
Difficult as ideally need to see information when the seizure takes place, which is not predictable.
There is a high incidence of misdiagnosis, even with specialists.
Is an EEG definitive?
No, between 20-40% of patients with epilepsy have normal EEG and 15% of patients without epilepsy have abnormal EEG, so again it can only support other information.
What is the pathology of a seizure?
Increased excitability causes neurones to fire, and there are three main mechanisms by which this can occur.
Membrane depolarisation irregularities where small areas reach AP more quickly than normal, can be due to build up of potassium, change in sodium or calcium.
Increased excitatory input - glutamate Or EAA( excitatory amino acid)
Decreased inhibitory imput - GABA
What is the seizure sequence and how does this differ between partial and generalised seizures?
- Initiation from an abnormal voltage gated channel. This is whee the seizure starts.
- Synchronisation, where it spreads to a small group of local neurons that have abnormal receptor operated channels.
This is how a small area is affected, as one neurone would probably not be noticed, but it is the small group going together that causes the seizure.
Sometimes it spreads to other parts of the brain through normal neurones due to the way they are connected. This is propagation and is how generalised seizures affect areas that are not initially acting abnormally.
What are some different symptoms that may be experienced during a seizure?
Absence - blank, unresponsive (petit Mal)
Tonic clonic - unconscious, muscle become stiff(tonic) then shake and jerk (clonic) and often very tired afterwards. (Grand Mal)
Atonic - muscle relax
Myoclonic - muscle jerk
Are seizures limited to epilepsy?
No, any of th types of seizure can be caused by other conditions, such as fever, or occur once without a known cause. Epilepsy is a term that is given only when a person has suffered from two or more seizures.
What should you do if a person has a seizure?
If the seizure does not abate, phone an ambulance as it is abnormal.
If seizing make sure the area is clear so damage does not occur rom hitting off of objects.
What are the main strategies for treatment of epilepsy?
Stabilise membrane and prevent depolarisation by action on ion channels.
Increase inhibitory GABA transmission
Decrease excitatory glutamate transmission
What is an example of a drug used in epilepsy which affects sodium channels?
Phenytoin is a very effective drugs, but is not normally a first line choice anymore. It can be used for status epilepticus, or when the patient has not responded to the first line drugs.
It works by acting on sodium channels, by prolonging the closure of inactivation gates in the channel. During inactivation, there is no sodium influx, so there is an increased refractive period between firing. This reduces rapid repetitive firing.
