Epilepsy: a very basic introduction

Epilepsy: a very basic introduction

Epilepsy is a common neurological condition characterised by recurrent seizures. There are around 500,000 people in the UK with epilepsy, of whom around two-thirds achieve satisfactory seizure control with antiepileptic medication.

Epilepsy most commonly occurs in isolation although certain conditions have an association with epilepsy:

• cerebral palsy: around 30% have epilepsy
• tuberous sclerosis
• mitochondrial diseases

It should be remembered that epilepsy is not the only reason people have seizures. The table below shows some of the more common causes of recurrent seizures seen in clinical practice. Patients may of course develop one-off seizures following any insult to the brain, for example infection, trauma or metabolic disturbance.

Disorder	Notes
Febrile convulsions	typically occur in children between the ages of 6 months and 5 years around 3% of children will have at least one febrile convulsion usually occur early in a viral infection as the temperature rises rapidly seizures are typically brief and generalised tonic/tonic-clonic in nature
Alcohol withdrawal seizures	occur in patients with a history of alcohol excess who suddenly stop drinking, for example following admission to hospital chronic alcohol consumption enhances GABA mediated inhibition in the CNS (similar to benzodiazepines) and inhibits NMDA-type glutamate receptors.Alcohol withdrawal is thought to be lead to the opposite (decreased inhibitory GABA and increased NMDA glutamate transmission) the peak incidence of seizures is at around 36 hours following cessation of drinking patients are often given benzodiazepines following cessation of drinking to reduce the risk
Psychogenic non-epileptic seizures	previously termed pseudoseizures, this term describes patients who present with epileptic-like seizures but do not have characteristic electrical discharges patients may have a history of mental health problems or a personality disorder

Classification of seizures

Seizures are generally classified as being either generalised or partial:

• generalised: consciousness is lost immediately. There are no focal features.
• partial: focal features are present. May progress to become a generalised seizure

Examples of generalised seizure sub-types:

• grand mal (tonic-clonic): tonic phase of muscle contraction followed by repeated contraction and relaxation of muscles
• petit mal (absence seizures): typically a brief (around 10 second) episode where the patient appears/blank or like they are 'staring'
• myoclonic: brief, rapid muscle jerks
• atonic seizures: 'drop attacks', patients lose muscle tone and drop to the ground
• partial seizures progressing to generalised seizures

Examples of partial seizure sub-types:

• simple (no disturbance of consciousness or awareness)
• complex (consciousness is disturbed)
• temporal lobe → aura, déjà vu, jamais vu; motor → Jacksonian

In addition a number of special forms of epilepsy are recognised in children:

Syndrome	Notes
Infantile spasms (West's syndrome)	Brief spasms beginning in first few months of life 1. Flexion of head, trunk, limbs → extension of arms (Salaam attack); last 1-2 secs, repeat up to 50 times 2. Progressive mental handicap 3. EEG: hypsarrhythmia usually 2nd to serious neurological abnormality (e.g. TS, encephalitis, birth asphyxia) or may be cryptogenic poor prognosis
Lennox-Gastaut syndrome	May be extension of infantile spasms (50% have hx) onset 1-5 yrs atypical absences, falls, jerks 90% moderate-severe mental handicap EEG: slow spike ketogenic diet may help
Benign rolandic epilepsy	paraesthesia (e.g. unilateral face), usually on waking up
Juvenile myoclonic epilepsy (Janz syndrome)	Typical onset in the teens, more common in girls 1. Infrequent generalized seizures, often in morning 2. Daytime absences 3. Sudden, shock like myoclonic seizure usually good response to sodium valproate

Symptoms and signs

As well as the seizure activity described above patients who have had generalised seizures may

• bite their tongue
• experience incontinence of urine

Asking about such features can be useful way of detecting epileptic seizures when taking a history from a patient who presents with a 'blackout' or 'collapse'.

Following a seizure patients typically have a postictal phase where they feel drowsy and tired for around 15 minutes.


Investigations

Following their first seizure patients generally have both an electroencephalogram (EEG) and neuroimaging (usually a MRI).


Management

Most neurologists now start antiepileptics following a second epileptic seizure. 

As a general rule:

• sodium valproate is used first-line for patients with generalised seizures
• carbamazepine is used first-line for patients with partial seizures

Antiepileptics are one of the few drugs where it is recommended that we prescribe by brand, rather than generically, due to the risk of slightly different bioavailability resulting in a lowered seizure threshold.

It is useful when thinking about the management of epilepsy to consider certain groups of patients:

• patients who drive: generally patients cannot drive for 6 months following a seizure. For patients with established epilepsy they must be fit free for 12 months before being able to drive
• patients taking other medications: antiepileptics can induce/inhibit the P450 system resulting in varied metabolism of other medications, for example warfarin
• women wishing to get pregnant: antiepileptics are generally teratogenic, particularly sodium valproate. It is important that women take advice from a neurologist prior to becoming pregnant, to ensure they are on the most suitable antiepileptic medication. Breast feeding is generally considered safe for mothers taking antiepileptics with the possible exception of the barbiturates
• women taking contraception: both the effect of the contraceptive on the effectiveness of the anti-epileptic medication and the effect of the anti-epileptic on the effectiveness of the contraceptive need to be considered

The table below looks at some of the more commonly used antiepileptics:

Drug	Mechanism of action	Uses	Adverse effects
Sodium valproate	Increases GABA activity	First-line for generalised seizures	increased appetite and weight gain alopecia: regrowth may be curly P450 enzyme inhibitor ataxia tremor hepatitis pancreatitis thrombocytopaenia teratogenic (neural tube defects)
Carbamazepine	Binds to sodium channels increasing their refractory period	First-line for partial seizures	P450 enzyme inducer dizziness and ataxia drowsiness leucopenia and agranulocytosis syndrome of inappropriate ADH secretion visual disturbances (especially diplopia)
Lamotrigine	Sodium channel blocker	Used second-line for a variety of generalised and partial seizures	Stevens-Johnson syndrome
Phenytoin	Binds to sodium channels increasing their refractory period	No longer used first-line due to side-effect profile	P450 enzyme inducer dizziness and ataxia drowsiness gingival hyperplasia, hirsutism, coarsening of facial features megaloblastic anaemia peripheral neuropathy enhanced vitamin D metabolism causing osteomalacia lymphadenopathy

Acute management of seizures

Most seizures terminate spontaneously. When seizures don't terminate after 5-10 minutes then it is often appropriate to administer medication to terminate the seizure. Patients are often prescribed these so family members may administer them in this eventuality, often termed 'rescue medication'. Benzodiazepines such as diazepam are typically used are may be administered rectally or intranasally/under the tongue. 

If a patient continues to fit despite such measures then they are termed to have status epilepticus. This is a medical emergency requiring hospital treatment. Management options include further benzodiazepine medication, infusions of antiepileptics or even the use of general anaesthetic agents.

Posted in: Notes : Neuroscience