What types of seizures are there?
Seizures may vary from the briefest lapses of attention or muscle jerks to severe and prolonged convulsions. They may also vary in frequency, from less than one a year to several per day. Seizures are classified according to where in the brain they arise. The International Classification of Epileptic Seizure identifies seizure types by the site of origin in the brain. The two main categories of seizures include partial seizures and generalized seizures. A partial seizure can evolve to a
generalized seizure. There are several subtypes of each. Only the most common are described here.
Partial or focal seizures: These seizures arise from an electric discharge of one or more localised areas of the brain regardless of whether the seizure is secondarily generalized. Depending on their type, they may or may not impair consciousness. Whether seizures are partial or focal, they begin in a localized area of the brain, but then may spread to the whole brain causing a generalized seizure. Partial seizures only involve a localised part of the brain, whereas generalised seizures involve the entire cortex. The term 'secondary generalisation' may be used to describe a partial seizure that later spreads to the whole of the cortex and becomes generalised.
Partial seizures may be further subdivided into simple and complex seizures. This refers to the effect of such a seizure on consciousness; simple seizures cause no interruption to consciousness (although they may cause sensory distortions or other sensations) whereas complex seizures interrupt consciousness. This does not necessarily mean that the person experiencing this sort of seizure will fall unconscious (like a faint). For example, complex partial seizures may involve the unconscious repetition of simple actions, gestures or verbal utterances.
The effects of partial seizures can be quite dependent on the area of the brain in which they are active. For example, a partial seizure in areas involved in perception may cause a particular sensory experience (for example, the perception of a scent, music or flashes of light) whereas when centred in the motor cortex a partial seizure might cause movement in particular groups of muscles. This type of seizure may also produce particular thoughts or internal visual images or even experiences which may be distinct but not easily described. Seizures centred on the temporal lobes are known to produce mystical or ecstatic experiences in some people. These may result in a misdiagnosis of psychosis or even schizophrenia, if other symptoms of seizure are disregarded and other tests are not performed. Unfortunately for those with epilepsy, anti-psychotic medications prescribed without anti-convulsants in this case can actually lower the seizure threshold further and worsen the symptoms. In about half of cases of temporal lobe epilepsy, very strong ictal headaches may occur, often misdiagnosed as migraine with aura. However, these headaches may be much more intense, and are sometimes even accompanied by temporary blindness.When these effects appear as a 'warning sign' before a more serious seizure they are known as an aura and may be the result of a partial seizure which later becomes generalised
Generalized seizures: these seizures affect the whole body and take two forms: Generalized absence and tonic-clonic. The electrical discharge which leads to these seizures involves the whole brain and may cause loss of consciousness and/or muscle contractions or stiffness. They include what used to be known as "grand mal" convulsion and also the brief "petit mal" absence of consciousness. Normally, the brain's nerve cells (neurons) communicate with one another by firing tiny electric signals that pass from cell to cell. The firing pattern of these electric signals reflects how busy the brain is. The location of these signals indicates what the brain is doing, such as thinking, seeing, feeling, hearing, controlling the movement of muscles, etc. A seizure occurs when the firing pattern of the brain's electric signals suddenly becomes very abnormal and unusually intense, either in an isolated area of the brain or throughout the brain. If the whole brain is involved, the electrical disturbance is called a generalized seizure. This type of seizure used to be called a grand mal seizure. The most easily recognizable symptom of a generalized seizure is the body stiffness and jerking limbs known as tonic-clonic motor activity.
Generalised seizures can be sub-classified into a number of categories, depending on their behavioural effects: Absence seizures (sometimes referred to as petit mal seizures) involve an interruption to consciousness where the person experiencing the seizure seems to become vacant and unresponsive for a short period of time (usually up to 30 seconds). Slight muscle twitching may occur. Tonic-clonic seizures (sometimes referred to as grand mal seizures), involve an initial contraction of the muscles (tonic phase) which may involve tongue biting, urinary incontinence and the absence of breathing. This is followed by rhythmic muscle contractions (clonic phase). This type of seizure is usually what is referred to when the term 'epileptic fit' is used colloquially. These tend to be accompanied by intense visions or hallucinations often of a mystical or religious nature. The epileptic may, upon regaining consciousness, hold very strong beliefs deriving from their experience that may persist for some time. Myclonic seizures involve sporadic muscle contraction and can result in jerky movements of muscles or muscle groups. Atonic seizures involve the loss of muscle tone, causing the person to fall to the ground. These are sometimes called 'drop attacks' but should be distinguished from similar looking attacks that may occur in narcolepsy or cataplexy. Status epilepticus refers to continuous seizure activity with no recovery between successive tonic-clonic seizures. This is a life threatening condition and emergency medical assistance should be called immediately if this is suspected. A tonic-clonic seizure lasting longer than 5 minutes (or two minutes longer than the usual seizures for a given epileptic) is usually considered grounds for calling the emergency services.
More information on epilepsy (seizures)
What is epilepsy? - Epilepsy is a general term that includes various types of seizures. Epilepsy is characterized by unprovoked, recurring seizures that disrupt the nervous system.
What are seizures? - Seizures (or convulsions) are temporary alterations in brain functions due to abnormal electrical activity of a group of brain cells that present with apparent clinical symptoms and findings.
What types of seizures are there? - The two main categories of seizures include partial seizures and generalized seizures. A partial seizure can evolve to a generalized seizure.
What types of epilepsy are there? - There are several types of epilepsy. Epilepsy can be divided into two broad categories: idiopathic epilepsy and symptomatic epilepsy.
What're the common types of epilepsy? - The most common types of epilepsy are absence epilepsy, temporal lobe epilepsy, frontal lobe epilepsy, occipital lobe epilepsy, and parietal lobe epilepsy.
What causes epilepsy? - Epilepsy may be caused by a number of unrelated conditions, including damage resulting from high fever, stroke, toxicity, or electrolyte imbalances.
What causes children epilepsy? - There are many possible causes of epilepsy in children. Seizures in infants and children may be due to birth defects, difficulties during delivery, or poisoning.
What factors will trigger epilepsy? - The triggers of epilepsy include inadequate sleep, food allergies, alcohol and smoking, flashing lights, developmental anomalies, and brain tumours.
What're the symptoms of epilepsy? - There are many forms of epilepsy, each with its own characteristic symptoms. The basic symptom of epilepsy is a brief and abnormal phase of behavior.
How is epilepsy diagnosed? - Making an accurate diagnosis is vital in planning the correct treatment to control seizures. Taking a medical history can help rule out non-epilepsy conditions.
What're the treatments for epilepsy? - For most people with epilepsy, treatment can reduce or prevent seizures and allow many patients to remain free of seizures for the rest of their lives.
What epilepsy medications are available? - Epilepsy is often treated with medication, neurocybernetic prostheses. Medications available for the treatment of seizures include phenytoin, carbamazepine, divalproex.
What epilepsy surgeries are available? - Surgical techniques to remove injured brain tissue may be appropriate for many patients with epilepsy. The most common surgery for epilepsy is temporal lobectomy.
What is vagus nerve stimulation? - Vagus nerve stimulation is a recently developed form of seizure control which uses an implanted electrical device.
What epilepsy diet is suggested? - It is believe that a restricted caloric intake while on a balanced diet can lead to measurable seizure reduction among all age groups.
How to prevent epilepsy? - Effective actions for the prevention of epilepsy include adequate pre-natal and post-natal care, safe delivery, control of fever in children, control of parasitic diseases.
Epilepsy in children - Epilepsy is a common childhood disorder. The prospect of control by means of anti-epileptic drugs is good in most children with epilepsy.
Pregnancy and epilepsy - Women with epilepsy who become pregnant have a higher risk for complications than women who don't have epilepsy.
Difference between seizures and epilepsy - Seizures are a symptom of epilepsy. Epilepsy is the underlying tendency of the brain to produce a sudden burst of electrical energy.
What's a grand mal seizure? - A grand mal seizure is a seizure involving the entire body, usually characterized by muscle rigidity, violent rhythmic muscle contractions, and loss of consciousness.
What's absence seizure (petit mal seizure)? - Absence seizure e - also known as petit mal seizure - is a type of seizure that most often occurs in children.
What is a febrile seizure? - A febrile seizure is a convulsion in a child triggered by a fever. A febrile seizure may be as mild as the child's eyes rolling or limbs stiffening.
What are epileptic seizures? - An epileptic seizure, often referred to as a fit, occurs when there is an abnormal discharge of neurones in the brain.
What is status epilepticus? - Status epilepticus is a continuous seizure state. Status epilepticus is most often caused by not taking anticonvulsant medication as prescribed.
What causes seizures? - Seizures may be caused by many conditions, diseases, injuries, and other factors. Injuries that may cause seizures include choking, head injury.