Epilepsy Flashcards
Clinically define epilepsy
Epilepsy is the excessive a synchronous activity of central neurones manifesting as a seizure on more than one occasion. It is important to be wary when defining epilepsy, since it has huge social, medical and financial implications.
Describe the change in neuronal activity from a normal state to a seizure
During an epileptic seizure neuronal foreign is synchronous throughout the brain. Normally neurones should fire asynchronously.
Describe the difference between a partial and a generalised epileptic seizure
A partial epileptic seizure is associated with focal neuronal overactivity limited to a single hemisphere of the brain. A partial seizure can be either simple or complex.
A generalised epileptic seizure is associated with excessive neuronal activity which has spread to both hemispheres of the brain, resulting in impaired consciousness. These can range from a grand-mal (tonic-clonic) seizure to a petit-mal (absence) seizure.
Describe some of the main causes of morbidity in epilepsy
Injury during fall resulting in epidural or subdural haematoma formation.
SUDEP - sudden death in epilepsy
Respiratory depression during status epilepticus
If death does not occur it can result in brain injury permanently.
What is status epilepticus and how is it treated?
Status epilepticus is a state in which an epileptic fit is cycled and lasts longer than five minutes. This is a medical emergency.
Treatment focuses on maintaining the airway and reducing the likelihood of injury initially (first aid). Definitive treatment is often through administration of phenytoin (due to its zero-order kinetics it can reach therapeutic concentrations quickly) or benzodiazepines such as diazepam or lorazepam.
Where treatment is not effective ICU sedation can be carried out.
Outline the symptoms of a partial seizure.
Symptoms of a seizure depend on the type of seizure it is and the part of the brain affected.
For example in a simple partial seizure a patient can experience abnormal sensations such as hallucinations, smells, sounds or pain for example. They may also experience muscle contractions or changes in behaviour if the frontal lobe is affected.
In a complete partial seizure the patient has impaired consciousness in that they have lost awareness (however retain wakefulness). These patients may then have altered behaviour, altered muscle contractions or altered sensation.
Outline the symptoms of a generalised seizure
A generalised seizure affects both hemispheres of the brain as well as the brainstem and so consciousness will be lost.
The symptoms depend on the type of generalised seizure experienced. For example in a tonic-clonic seizure a patient initially collapses due to an increase in muscle tone, followed by periods of repeated muscular contractions known as “clonus”.
An absence seizure results in a patient staring into space and they cannot be disturbed.
Other seizures include clonic seizures, tonic seizures and myoclonic seizures.
Describe some of causes of epilepsy
Head injury, vascular disease/stroke, hereditary channelopathies, hypoxic brain injury, meningitis.
State some of the common triggers of an epileptic seizure
Alcohol, sensations (lights, sounds, tastes), stress, tiredness, not taking medication.
What are the two main classes of drug used to treat epilepsy? Name all examples of each
Na channel blockers (voltage-dependant):
- carbamazepine
- phenytoin
- lamotrigine
GABA enhancement:
- valproate
- Benzodiazepines (diazepam, lorazepam)
Contrast the elimination kinetics of phenytoin and carbamazepine.
Phenytoin has non-linear pharmacokinetics meaning that the ADME system is saturated and zero-order kinetics are followed. Administration of the drug continually at the same therapeutic dose can cause an overdose.
Carbamazepine follows first order kinetics and is linear. This means that a constant proportion of drug is removed from the blood as a given time period. The drug can be given at continued therapeutic doses without an increased risk of toxicity - HOWEVER: carbamazepine is an inducer of the CYP450 system and so can induce its own metabolism, meaning subsequent drug half lives are reduced.
