Seizure
Definition
A seizure is hypersynchronous neuronal activity. "Hypersynchronous", in plain English, means "unsynchronised" and "a lot". So a seizure is a lot of unsynchronised neuronal activity.
Epidemiology
Fairly common.
Pathophysiology
A seizure is a surge of electrical activity in the brain, often passing across anatomical boundaries, causing misfunction of the stuff it passes. Sometimes they are small and only affect a small thing, such as a twinge in a finger. Sometimes they are large and cause loss of consciousness and flailing arms and stuff.
They are often caused by an abnormality, such as a tumour, or a birthmark on the brain. Often someone will have one, and never have another, and are just idiopathic.
The commonest seizure is tonic-clonic. This means there is an initial stage where all the muscles tense (tonic), then shake (clonic). For more information on types of seizure, visit the epilepsy page and its classification of seizures.
Clinical and Associated Features
There are 6 main types:
- Tonic-clonic seizure - This type of seizure has two stages. Your body will become stiff and then your arms and legs will begin twitching. You will lose consciousness and some people will wet themselves. This is classic epilepsy.
- Absences - mainly affects kids. The child will seem to just stare vacantly into space, although some children will flutter their eyes or smack their lips. No memory of the period they are gone.
- Partial seizures - often just change one small thing, so a single motor disturbance, personality change, strange feelings. These are the only non generalised seizures.
- Myoclonic jerks - Sudden one off jerks of limbs.
- Atonic seizure - This causes all of your muscles to suddenly relax, so you fall over.
- Tonic seizure - This causes all of your muscles to suddenly contract, so you fall over.
Medical Emergency - Status epilepticus is when a seizure last for more than half an hour, or the patient does not regain consciousness!
Differential Diagnosis
- Epilepsy.
- Head injury.
- Fever, causing febrile convulsions.
- Infection - especially meningitis and encephalitis.
- Metabolic problems such as hypoglycaemia, hypoxia and hyponatremia, or thyroid storm.
- Eclampsia.
- Increased ICP, commonly from brain haemorrhage or brain tumour.
- Drug abuse or medication withdrawal.
Investigations
You want to screen for the underlying cause. If a patient suddenly has a seizure with no history, you want to screen for intracranial causes with a head CT, and do some bloods/ABG in order to rule out the metabolic causes.
Next step is an EEG to scan the brain's electrical patterns. It's most effective during a seizure, but some people with epilepsy will have abnormal patterns even when they are not in the middle of a seizure.