Seizures are caused by abnormal electrical activity in the brain. In the healthy brain, electrical and chemical signals are fired between nerves called neurons to drive the brain's ability to think, feel and send instructions to parts of the body, such as the muscles. Seizures occur when this electrical system in the brain malfunctions.
There are many causes of seizure including fever, injury, disease and the use of certain medications. When seizures occur on a regular basis due to a brain disorder, this is called epilepsy.
Symptoms of seizures
Seizures may cause dramatic symptoms such as uncontrollable muscle movement, frothing at the mouth and violent shaking, along with blackout and confusion. However, symptoms can also be mild, with few physical symptoms and a person merely appearing to stare into space and not be paying attention.
There are several types of seizure including non-epileptic seizures which may arise from a head injury or illness, for example, as well as partial and generalized seizures, which are associated with epilepsy. Partial seizures arise from abnormal activity in one part of the brain.
Symptoms may vary according to where exactly that abnormality is, but examples include a wave-like sensation, a sense of déjà vu, numbness, tingling and visual disturbances such as hallucination.
Abnormal electrical activity involving a larger portion or the whole of the brain are referred to as generalized seizures. Examples of generalized seizure include:
Absence seizure - Where a person appears inattentive for a short period.
Myoclonic seizure - Characterized by muscle twitching.
Clonic seizure - Where the sufferer experiences involuntary muscle spasms.
Tonic-clonic seizure - the form most commonly associated with epilepsy. In tonic-clonic seizure, the skeletal muscles stiffen up causing the body to contract (tonic phase) and this is followed by convulsions and vibration of the stiffened limbs (clonic phase).
Another type of generalized seizure is atonic seizure, also called a drop seizure, which is usually noticeable as a drooping of the head as strength in the head and neck muscles is lost. Although the seizure itself is not damaging, the loss of muscle tone can cause a person to fall and hurt themselves. Warning signs that may precede a seizure include a sense of fear or anxiety, nausea, dizziness and visual disturbances.
Recurrent and unprovoked seizures are diagnostic for epilepsy but seizures may also occur in people who do not have epilepsy due to other causes such as severely low blood sugar, brain tumours, infection or injury. Therefore, diagnosis of epilepsy involves ruling out any other such underlying causes.
Diagnosis involves an assessment of clinical symptoms and the details of the seizure experienced, followed by an electroencephalogram (EEG) to examine the brain's electrical activity.
A large range of antiepileptic medications are available. These medications prevent repeated firing of the electrical impulses in the brain. Regular use of antiepileptic drugs can prevent the complications of epilepsy such as accidents brought about during convulsions or sudden loss of muscle tone.
Most antiepileptic drugs, however, are not free from side effects, especially in the case of long-term use. Some examples of antiepileptic agents include phenytoin, carbamazepine, sodium valproate, topiramate and lamotrigine.
Reviewed by Sally Robertson, BSc