Epilepsy is a medical condition characterized by spontaneous recurrent seizures. Seizures are brief neurological symptoms resulting from abnormal discharge or “firing” of neural brain cells in the cerebral cortex.
Neurons normally transmit information by firing a single short discharge that is conducted from one neuron to another. Seizures result when the discharge is prolonged or recurs rapidly and recruits other neurons. The synchronous discharge of neurons causes excessive expression of the activity normally performed by the discharging brain region.
The symptoms caused by a seizure are determined by the brain region involved. Simple partial (or focal) seizures result from discharge of a small brain region. Seizures arising in the frontal lobe primary motor cortex cause motor seizures. This region contains the neurons of motor control that are eventually connected to muscles in the arms and legs; a seizure arising in the hand region of the primary motor cortex causes jerking of the opposite hand. Simple partial sensory seizures arise in the parietal lobe primary sensory area and cause abnormal sensations. Seizures arising in the occipital lobe primary visual area cause visual symptoms.
Complex partial seizures are the most common seizure type in adults. They most often begin in the temporal lobe, which is normally responsible for memory. They are characterized by 1 to 3 minutes of nondistractible staring, often with automatisms of manipulating objects or lip smacking, and are followed by confusion and amnesia for the event.
Generalized tonic-clonic seizures, previously termed grand mal or convulsions, are characterized by sudden unresponsiveness, whole body stiffening (tonic phase), and falling to the ground. This evolves to typically less than 3 minutes of rhythmic muscle jerking (clonic phase), followed by deep sleep. “Generalized” seizures begin throughout the whole brain simultaneously. Secondary generalized tonic-clonic seizures start in one brain region, or focus, and spread to the whole brain.
There are other types of generalized seizures. Absence seizures, previously termed petit mal, cause 5 to 20 seconds of nondistractible staring, often occurring multiple times daily in children. Tonic seizures cause whole body stiffening. Clonic seizures cause whole body jerking. Myoclonic seizures are brief lightning-like jerks. Infantile spasms are brief contractions of the infant’s trunk, typically in clusters and accompanied by developmental delay.
Approximately 10% of people will have a seizure. Less than 3% will have epilepsy; 7% will have only a single seizure, often provoked by a transient cause such as alcohol withdrawal, trauma, drugs, or a medical illness.
Any brain disease that affects the cerebral cortex can cause seizures and therefore cause epilepsy. However, “epilepsy” is often reserved for illnesses in which seizures are the primary manifestation. The most characteristic epilepsy syndromes cause generalized seizures from abnormalities of neural transmission without structural brain abnormalities. A few are inherited in a traditional manner but most are sporadic.
Epilepsy with visible structural brain abnormalities can be acquired, for example, from perinatal asphyxia, brain infections, or tumors, or following trauma or stroke. Developmental brain malformations are a congenital cause. The cause of epilepsy is unknown in 50% of patients.
Epilepsy is diagnosed based on the presentation of seizures, but some tests support it. An electroencephalogram (EEG) demonstrates spikes in brainwave activity in about 40% of patients. Brain magnetic resonance imaging (MRI) and computed tomography (CT) visualize a structural abnormality in a minority.
Antiepileptic drugs (AED) are the mainstay of therapy. Effectiveness depends on the seizure type, cause, and epilepsy syndrome. The first AED tried is effective in preventing recurrence of seizures in about 50% of patients. Another 20% will respond to the second or third AED. Approximately 30% remain refractory to AEDs. When seizures arise from a single brain region, surgery to remove the seizure focus is considered. Temporal lobectomy is the most common epilepsy surgery, rendering 70% of patients essentially seizurefree. Transient or mild complications occur in about 15%. Vagus nerve stimulation and the ketogenic diet are also treatments.
The previous social stigma of epilepsy being associated with mental retardation or mental illness is dispelled, as most patients are mentally normal. Most state laws prohibit driving for 6 to 12 months after a seizure, which interferes with transportation to work and social interactions, resulting in underemployment, undereducation, and social isolation.
- American Epilepsy Society, http://www.aesnet.org
- Commission on Classification and Terminology of the International League Against Epilepsy. (1981). Proposal for the revised clinical and electroencephalographic classification of epileptic Epilepsia, 22(4), 489–501.
- Commission on Classification and Terminology of the International League Against Epilepsy. (1989). Proposal for revised classification of epilepsies and epileptic syndromes. Epilepsia, 30(4), 389–399.
- Engel, , & Pedley, T. A. (1998). Epilepsy: A comprehensive textbook. Philadelphia: Lippincott-Raven.
- Epilepsy Foundation of America, http://www.epilepsyfoundation.org/
- International League Against Epilepsy (ILAE), http://www.ilae-epilepsy.org
- National Institute of Neurological Disorders and Stroke, http://www.ninds.nih.gov/
- Shorvon, , Dreifuss, F., Fish, T., & Thomas, D. (1996). The treatment of epilepsy. Oxford, UK: Blackwell Science.