From epilepsy.com

Why Do I Have Seizures?

The most common question in an initial epilepsy clinic visit is “Why do I have seizures”? Since seizures come like bolts from the blue, it is easy to understand the old superstitions that ascribed seizures to supernatural forces. But seizures and epilepsy (the condition of spontaneously recurrent seizures) have natural physical causes. What are these causes?

The medical word for “cause” is “etiology.” Etiology of seizures varies with the type of seizure, whether it starts focally in one part of the brain or whether it is apparently generalized all over the brain at the start. Examples of partial-onset seizures are simple partial (e.g., auras, focal motor), complex partial (previously called psychomotor or temporal lobe seizures) and secondarily generalized seizures. Generalized-onset seizures include absence (petit mal), tonic-clonic (grand mal), atonic (drop attacks), and myoclonic (sudden jerk) seizures. More information on types of seizures can be found on epilepsy.com at http://www.epilepsy.com/epilepsy/types_seizures and the video series at http://www.epilepsy.com/node/3007.

Focal Seizures

Focal seizures are caused by injury or malfunctioning of one or more parts of the brain. A brain injury may generate an immediate (defined loosely as being within one week of an injury) seizure, but these early seizures often do not lead to later seizures. If recurrent seizures arise more than a week after an injury, then the condition is considered epilepsy. The onset of seizures after a brain injury often occurs after such a delay, even of many years. Researchers believe that this delay results from reorganization of nerve connections in the injured areas. The brain makes an attempt to fix the injury by growing new connections, but the result is a circuit that is more electrically excitable and prone to produce seizures. Here are some of the common brain injuries or conditions that may lead to epilepsy. These etiologies often (but not always!) can be revealed by a brain MRI.

Head trauma: The bumps on the head and the falls from the swings that all children experience are usually too mild to produce epilepsy. But epilepsy can result from head trauma severe enough to produce many hours of loss of consciousness or amnesia, penetrating injury of the brain or bleeding in the brain. A special exception is an immediate seizure from minor head trauma, for example, getting hit in the head by a soccer ball. This is called a concussive convulsion, and it rarely leads to subsequent seizures.

Stroke: We are increasingly recognizing seizures that occur for the first time in senior citizens. Our presumption is that many of these are a consequence of a brain injury from a previous stroke. During a stroke, brain cells die or are injured by blockage of blood flow to a part of the brain. About 10% of strokes lead to subsequent epilepsy. Some of these strokes may be so small as to have gone unnoticed, and may be detected only by a CT or MRI brain scan. Related to strokes is brain hemorrhage, which also can be an etiology for epilepsy. A seizure after a stroke does not mean that there has been another stroke.

Infection: Worldwide, infection is probably the most common cause for focal seizures. Organisms that can cause seizures include bacteria, viruses, fungi or parasites (most importantly cysticercosis, a microscopic worm from bad pork). If the bug infects the lining of the brain, the condition is meningitis. If the brain is infected, it is called encephalitis. Seizures may occur at the time of a brain infection or after a delay. Some of those viral “colds” or “flu’s” that we had in the past, with headache, fever and confusion, may have included brain infections, leading later to seizures.

Vascular malformations: Abnormal blood vessels in the brain are common causes of epilepsy. Blood is brought to the brain by arteries. It flows into small capillaries, where oxygen is transferred to the brain cells, and then is carried out by veins. A malformation of arteries and veins is called an arteriovenous malformation (AVM). A malformation of capillaries is called a cavernous malformation or cavernous angioma. These malformations can be inborn or acquired after brain stresses, such as radiation. The brain cells near the malformation may be irritated by bleeding or lack of oxygen. The response to this irritation can be seizures.

Tumor: A brain tumor is a much-feared cause of seizures, but most seizures do not result from brain tumors. Brain tumors can be benign, malignant or sometimes in the borderland between the two. A common benign tumor is a meningioma (see figure), which grows from the cellophane-like lining of the brain and pushes on the brain, causing irritation and seizures. Tumors growing from brain include those named astrocytoma, oligodendroglioma, ganglioglioma, ependymoma and glioblastoma. A tumor that arises outside the brain can metastasize to brain.

Dysplasia: A dysplasia is a birth defect in the brain, consisting of abnormal but non-cancerous brain cells. Dysplasias are identified by MRI scans. Dysplasias do not grow or spread, but for unclear reasons, onset of seizures can be delayed until much later in life.

Mesial temporal sclerosis (MTS): This term literally means “inner temporal lobe scarring.” It shows on an MRI as a small bright hippocampus, which is a seizure-prone structure in the inner temporal lobe. MTS commonly is associated with complex partial seizures. Researchers debate whether MTS is a cause or a consequence of seizures. MTS can develop on the left, right or both sides of the brain. When only on one side, it may suggest the possibility of a surgical cure for the epilepsy, provided other testing confirms seizure origin from the region of MTS.

Genetic conditions: Genetic conditions usually produce generalized seizures, but a few exceptions produce focal seizures. Benign rolandic epilepsy (BRE), also called benign centrotemporal epilepsy, is such an exception. Children (more often boys) around the age of puberty have focal face or hand seizures, usually when falling asleep. The seizures can sometimes generalize to full body seizures. BRE is called benign because it is outgrown by the teenage years.

Generalized Seizures

Generalized Seizures result from brain cell networks on both side of the brain being activated apparently at once. Unlike focal seizures, no one place in the brain can be identified by neurological exam, EEG or MRI as being abnormal. Causes for generalized seizures fall into three broad categories.

Genetic: If one of a pair of identical twins has generalized seizures, the chances are more than 50-50 that the other twin will as well. Genetic, meaning inherited, factors are important etiologies of generalized epilepsies. These genetic factors provide the blueprints for the chemistry and wiring diagrams of the brain, and therefore the brain’s tendency to develop seizures. We are just beginning to identify the genetic basis for some types of epilepsy. Rarely is epilepsy caused by a mutation in only one gene. To pass epilepsy to children, a combination of genes, and also probably many environmental factors, is required. Most children of parents with epilepsy will not have epilepsy, but the risk is higher.

Metabolic: A wide variety of medical conditions can cause generalized seizures. As just a few examples, we can list low oxygen, low blood sugar, low blood sodium, low blood calcium, alcohol or sedative medication withdrawal, certain recreational or prescription drug overdoses, kidney or liver failure, hyperthyroid disease and toxemia of pregnancy. Enzyme deficiencies, often on a genetic basis, are important causes of seizures in young children. Metabolic causes produce seizures, but not epilepsy, since the seizures result from an immediate provoking factor, namely the metabolic derangement.

Febrile: A febrile seizure occurs in a child between the ages of 6 months and 6 years, in response to a fever. They are very common: approximately 3% of children will have at least one febrile seizure. Most febrile seizures are generalized, but a few are focal. The large majority of children with febrile seizures will not later develop epilepsy, and there is no evidence that treating with anti-seizure drugs influences the chance for later epilepsy.

Idiopathic Seizures

Idiopathic seizures are those whose cause is unknown. Unfortunately, about 60% of all seizures are idiopathic. In the case of focal seizures, we presume that there is an irritation to or scar on some part of the brain, but the scar is invisible to MRI. With generalized seizures, the genetic or metabolic abnormality is unidentified. Patients and families are mystified by the absence of answers, typified by the common refrain: “The doctor’s told me everything was normal.” As frustrating as this may be, two points should be reassuring. First, no tumor, stroke, infection, vascular malformation or other problem was found. Second, we do not need to know the cause to use medicines to treat the seizures. As MRI and other forms of imaging the brain continue to improve, more and more causes of seizures will be identified.

Robert S. Fisher, M.D., Ph.D.
Editor-in-Chief, epilepsy.com