Epilepsy

Description

Causes

A seizure's cause can be determined for about 28% of partial epilepsy patients. In the rest, however, epilepsy is idiopathic, which means that the cause is unknown. The age of seizure onset can sometimes offer a clue. In fact, idiopathic epilepsy is rare in children and young adults. According to a 2001 study, only 1% of cases in those age groups have no evident cause.

General Biologic Mechanisms Involved with Seizures

Epileptic seizures are triggered by abnormalities in the brain that cause a group of nerve cells in the cerebral cortex to become activated simultaneously, emitting sudden and excessive bursts of electrical energy that lead to seizures. Depending on the location in the brain where this electrical hyperactivity occurs, seizures have a wide range of effects on the sufferer, from brief moments of confusion to minor spasms to loss of consciousness.

Ion Channels. Sodium, potassium, and calcium act as ions in the brain. That is, they produce electric charges that must fire regularly in order for a steady current to pass from one nerve cell in the brain to another. If the ion channels that carry them are genetically damaged, a chemical imbalance occurs that can cause misfire and seizures. Abnormalities in the ion channels are believed to be responsible for absence and many other generalized seizures.

Neurotransmitters. Abnormalities may occur in neurotransmitters, the chemicals that act as messengers between nerve cells. Three neurotransmitters are of particular interest:

• The neurotransmitter gamma aminobutyric acid (GABA), which helps prevent nerve cells from over-firing. GABA deficiencies, then, are of particular interest to researchers in epilepsy. Recent discoveries of genetic factors involved in epilepsy that regulate the GABA signaling system are reinforcing the importance of this neurotransmitter in the disease process.
• Problems with the neurotransmitter serotonin are also being studied. This is an important brain chemical that is important for well-being and associated behaviors (eating, relaxation, sleep).
• Acetylcholine is a neurotransmitter in the cholinergic system, which is important for learning and memory, and is of interest in seizures.

Hippocampal Sclerosis. Hardened tissue (sclerosis) in the region of the brain called the hippocampus is the most commonly identified abnormality in patients with partial epilepsy. Such abnormal brain tissue involves structural reorganization and both loss and regeneration of nerve cells.

Genetic Factors

Dozens of genetic syndromes representing a variety of seizure patterns may account for the different forms this disease takes. The following epilepsy syndromes are known to be caused by single genetic defects:

• Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). ADNFLE is now believed to be caused by an alteration in a receptor in the brain called neuronal nicotinic acetylcholine.
• Benign familial neonatal convulsions (BFNC). BFNC appears to be caused by genetic defects that affect ion channels in nerve cells that carry potassium.

A genetic cause has been identified for at least some cases of juvenile myoclonic epilepsy, which represents 10% of all epilepsy cases. (Such research and other studies have pointed to the GABA signaling system as an important player in many cases of epilepsy.)

Known Causes of Childhood Seizures

Febrile Seizures. Febrile seizures are caused by high fever and usually occur between the ages of three months and five years. Between 10% and 15% of children with epilepsy have a history of febrile seizures before they develop the disease. It should be strongly noted, however, that febrile seizures are quite common and occur in about 3% of all children under five years old. Nearly all are brief and have no long-lasting effect.

Vaccinations. In young children, high fever from a vaccination can, in rare instances, trigger seizures, which are almost always temporary and have no serious consequences. Some controversy arose a few years ago over the possibility that the DTP (diphtheria-tetanus-pertussis) vaccine might trigger epilepsy or other neurologic diseases. Some experts suggest that children who have neurologic events following their DTP shot already have a preexisting impairment such as epilepsy, which is revealed but not caused by the vaccine. Children with existing epilepsy may be at risk for seizures two or three days after the vaccination. Such a temporary worsening of their disease does not appear to pose a danger to the child. Infants with suspected neurologic problems may have their vaccinations delayed until their neurologic situation is clarified, but not beyond their first birthday.

Head Injuries in Infants and Children. Infants are at high risk for head trauma. In fact, one study suggested that any infant with scalp fracture that occurs with a hematoma may be at risk for brain injury. A hematoma occurs after an injury when blood collects in a mass that usually looks like a large purplish area. It should be noted that hematoma is quite common after delivery when it typically causes no problems.

Childhood Viral Infections. According to a 2001 study of 22 children with status epilepticus (sustained periods of convulsions), viral testing uncovered the presence of several pediatric viruses. Human herpesvirus 6 was particularly associated with severe seizures. Herpesvirus 6 is common in children and causes roseola infantum, an acute illness that can lead to high fever and skin rash but is usually benign.

Hydrocephalus and Shunts. Hydrocephalus is a condition that may occur in newborns and infants in which cerebrospinal fluid (CSF) accumulates in the brain, leading to excessive swelling of the spaces in the brain (ventricles). The resulting pressure can damage the brain's tissue. Hydrocephalus itself is not commonly known to cause seizures, but its treatment, which involves insertion of a shunt, may be. The shunt is a device that drains the excess fluid from the brain to other parts of the body, as well as to a special reservoir that allows the shunt to be reached through the skin. One 2001 study noted that between 20% and 50% of shunted children may experience epileptic seizures, particularly if the shunt is placed before age two. More research on its relationship to epileptic seizures is clearly needed.

Focal Cortical Dysplasia. This is an abnormality in fetal development in which the normal migration of nerve cells is altered. It can cause very severe epilepsy that is difficult to treat.

Other Causes in Children. Seizures in infants and children may be due to birth defects, difficulties during delivery, or poisoning.

Causes of Seizures That Are Specifically Adult-Onset

Alcohol Abuse. Alcohol abuse is one of the most common causes of adolescent- and adult-onset seizures. Seizures, nearly always generalized tonic-clonic, occur in about 10% of adults during withdrawal, and in about 60% of these patients, the seizures are multiple. The first seizure occurs between seven and 48 hours after the last drink, and the time between the first and last seizure is usually six hours or less. [For more information, seeWell-Connected Report #56, Alcoholism.]

Head Injuries in Adults. Head injuries to adults can cause seizures, with the risk highest in severe head trauma. A first seizure related to the injury can occur years later. People with mild head injuries, which involve loss of consciousness for less than 30 minutes, have only a slight risk that lasts up to five years after the injury.

Sleep Disorders. Some sleep disorders, such as obstructive sleep apnea or narcolepsy, have been associated with seizures, although a causal relationship is unclear. In fact, sleep apnea and the hereditary nocturnal frontal lobe epilepsy have very similar symptoms (feeling of choking, abnormal motor activity during sleep, and excessive sleepiness during the day). In one 2000 study, one-third of patients with epilepsy that did not respond to medications were later diagnosed with obstructive sleep apnea. Some studies have found that when sleep apnea is treated in patients with both epilepsy and the sleep disorder, seizure activity decreases. More research is warranted on this subject.

Stroke. Seizure is also a symptom of a major stroke. In some cases, injury to the brain from small strokes may cause seizures. Studies report that between 15% and 23% of stroke patients consequently have seizures.

Other Causes in Adults. Other known or possible causes of epilepsy in teenage or adult years include the following:

• Drug abuse or withdrawal from drugs.
• Sudden withdrawal from certain antianxiety or antidepressant drugs.
• Occupational exposure to environmental triggers. High exposure to certain chemicals has been linked with seizures. A 2000 study of utility company employees in Denmark revealed an association between high exposure to electromagnetic fields (EMF) and an increased risk of epilepsy and neurologic diseases that affected motor control.
• Alzheimer's or other degenerative brain diseases in the elderly may cause seizures.
• In developing nations, nervous system infection by tapeworm larvae is an important cause of epilepsy.

Causes of Seizures That Can Occur at Any Age

Infections of the Brain and Central Nervous System. Brain infections can cause seizures during the acute infection, and some cases are complicated by brain damage that can lead to recurrent seizures afterward. The most common central nervous system infections are encephalitis and meningitis. Encephalitis is a brain inflammation often caused by infections transmitted by mosquitoes. Meningitis is an inflammation or infection of membranes covering the brain or spinal cord. One study found an association between epileptic seizures and herpes simplex virus infections that occur in the central nervous system. More research is needed before any causative role can be proved.

The organs of the central nervous system (brain and spinal cord) are covered by 3 connective tissue layers collectively called the meninges. Consisting of the pia mater (closest to the CNS structures), the arachnoid and the dura mater (farthest from the CNS), the meninges also support blood vessels and contain cerebrospinal fluid. These are the structures involved in meningitis, an inflammation of the meninges, which, if severe, may become encephalitis, an inflammation of the brain.

Hypoglycemia. Seizures can be caused by hypoglycemia, a complication of diabetes in both children and adults.

Brain Tumors. Both cancerous and noncancerous brain tumors can cause seizures in children and adults.

Cavernous Angiomas. Cavernous angiomas are blood vessels that grow abnormally and, like a tumor, can put pressure on nerve tissue.

Pseudoepilepsy. Between 20% and 45% of cases of untreatable seizures have a psychologic rather than physical origin. In this form of epilepsy, known as pseudoepilepsy or psychogenic epilepsy, the patient has no conscious intent of forcing a seizure and does not show unusual emotional behavior or signs of hysteria. It is very difficult to treat and can be very disabling. Pseudoepilepsy can usually be distinguished from true epilepsy using an electroencephalogram (EEG), which measures brain waves. The cause of pseudoepilepsy is unknown.