A seizure is an uncontrolled, abnormal burst of electrical and chemical activity that spreads rapidly between nerve cells (millions upon millions of them) in the brain.
A seizure may start in one region of the brain (the "focus") and spread to other parts.
The first symptoms of a seizure – referred to as the "aura", which often involves a strange sensation or smell – reflect the function of that area of the brain first affected by the epileptic activity.
A seizure that initially causes only twitching of one hand and then goes on to convulsions with loss of consciousness, for example, reflects seizure activity that starts in the front part of one hemisphere and then spreads to involve widespread areas on both sides of the brain.
Seizures have many differing causes and are a feature of various states of ill-health.
Seizures may be the only manifestation of disease, caused by a specific brain disorder, or are part of a more generalised bodily illness.
- Primary epilepsy refers to seizures where the brain is abnormally prone to seizure activity, probably due to an inherited tendency. These are often seen in children and teenagers.
- Secondary seizures, on the other hand, are typically due to spread from a seizure focus (a scar).
- Isolated seizures may be related to an underlying transient medical condition, and will stop as soon as the underlying condition is effectively treated. Examples include organ failure (liver or kidney failure), infections such as meningitis, head injury, brain surgery, drug and alcohol abuse.
In all forms of epilepsy, stress, sleep deprivation, a change in diet or medication, alcohol, certain specific activities as well as menstruation and pregnancy in women may precipitate individual seizures.
Professor Jonathan Carr, FCP (SA) Neurology, PhD. Head Division of Neurology, Tygerberg Hospital and University of Stellenbosch, Cape Town. February 2015.