A seizure is caused by abnormal electrical activity in the brain resulting in a short disturbance of consciousness, muscle function, sensations, behaviour, emotions, or a combination of these.
Seizures can be classified as generalised (where the electrical activity affects all of the brain) or focal (where the electrical activity stays in one part of the brain).
High temperatures, low oxygen levels, low blood sugar levels or poisons can cause a seizure.
Epilepsy however is defined by having at least two unprovoked seizures more than 24 hours apart. 1 in 100 people have epilepsy in the UK.
In generalised seizures the symptoms tend to involve the whole body and are accompanied by impaired consciousness. Types of generalised seizure are defined by their symptoms:
- Tonic seizures – stiffening of the body;
- Clonic seizures – jerking movements due to uncontrolled muscle contractions;
- Tonic-clonic seizures – the most common generalised seizure. Involves stiffening of the body with jerking movements;
- Absence seizures – brief loss of consciousness without changes to body tone or movements;
- Atonic seizures – body becomes limp and associated with falls;
- Myoclonic seizures – brief, sudden contraction of muscles.
Focal seizures depend on which part of the brain they start in:
- Focal motor seizures – jerking movement beginning in the hand and traveling up the arm or specific movements including head turning, eye movements and lip smacking;
- Focal sensory seizures – disturbances of one of either: sensations, emotions or behaviour.
People often experience symptoms after seizure including drowsiness, memory-impairment, injury and aching arms or legs.
In many people no cause for epilepsy can be identified.
Some people with epilepsy are susceptible to seizures after specific triggers including:
- Sleep deprivation;
- Low blood sugar levels;
- Strobe lighting;
- Alcohol excess;
In addition to a thorough history and examination other investigations are useful in helping diagnose epilepsy as other conditions may mimic seizures.
Blood tests and cardiovascular assessments such as ECGs, blood pressure monitoring and an echocardiogram can help rule out cardiac and metabolic causes for loss of consciousness.
An Electroencephalograph (EEG) can be used to record electrical activity of the brain. A normal test does not rule out epilepsy.
Brain scans using computer tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) can all be used to examine for specific underlying brain abnormalities.