Seizures and Epilepsy

by Denise Ewald Malkowicz, M.D.

Dr. Denise Malkowicz is a neurologist subspecializing in epileptology and clinical neurophysiology. She is board certified in neurology by the American Board of Psychiatry and Neurology. She is also board certified by the American Board of Psychiatry and Neurology with Added Qualifications in Clinical Neurophysiology. She has been a neurologist and epileptologist at a major university medical school. She had extensive experience in all aspects of treatment of persons with epilepsy, including standard medications, investigational drugs. and surgery in refractory cases.

Introduction

Many families find themselves in a position in which their child is diagnosed as having seizures or epilepsy. The terms used by the family doctor or neurologist may seem confusing. In some cases, the family may be given little explanation about the situation or the diagnosis. This article will attempt to define and clarify some of the medical terms you may encounter.

A Seizure or Epilepsy

A seizure is characterized by the sudden, excessive, chaotic electrical discharge of brain neurons which may manifest itself clinically by a change in "behavior". This change in behavior may include alterations in consciousness, perception, motor activity, sensation, or mentation. Seizures are usually episodic and brief and have a definite beginning and an end. After a seizure a person may return to his baseline pre-seizure state immediately, or within seconds, minutes or hours. Another word for a seizure is an "ictus". The words "ictal", an adjective referring to the seizure, and "postictal" an adjective referring to the state or the time period after a seizure, are commonly used terms.

Epilepsy is defined as a condition with a tendency for recurrent seizures. One may have a seizure without meeting the criteria for having "epilepsy". Approximately one out of every ten people (10%) will have a seizure sometime in his life, but only one or two people out of a hundred (1 or 2%) will be diagnosed as having epilepsy.

How Neurons Work

Neurons are specialized cells. Neurons carry electrochemical messages. Neurons signal other neurons and ultimately signal muscles, organs and glands. A chemical called a neurotransmitter is released from the terminal of one neuron and travels across a tiny gap called a synapse to bind to a special receptor site on the next neuron.

Neurotransmitters may open or change microscopic channels on the neuron. This permits ions (charged particles) like sodium and potassium to move across special channels in the membrane of the neuron. These ions carry charges which may cause further changes along the membrane. This results in an electrochemical discharge along the neuron.

When this reaches the end processes of the neuron, a neurotransmitter is again released to cross the synapse. The neurotransmitter bind to receptor on the other neuron and opens channels for ion exchange and the process continues.

Certain neurotransmitters are "inhibitory", opening up channels to ions that cause the neuron to become less likely to fire. Other neurotransmitters are "excitatory" opening ion channels that change the charges of the neuron to more likely to fire. An appropriate balance of excitation and inhibition allows orderly discharge of networks of neurons resulting in organized output or function.

This process can be adversely altered by a number of factors. Brain injury can cause structural disorganization or loss of neurons either focally or diffusely. Changes in biometabolism , exposure to toxins or certain drugs can effect neurotransmitters. Changes in electrolytes (ions), blood glucose or oxygen supply can also effect neuron function and metabolism. Genetically determined differences in brain structure or biochemistry can result in an abnormally or spontaneously "hyperexcitable" brain with a greater tendency to have seizure. This is sometimes referred to as a "low seizure threshold".

Seizure Threshold

The seizure threshold is the point beyond which a seizure occurs. The concept of seizure threshold is similar to that of resistance. Persons with "low seizure threshold" are more likely to have a seizure (less resistant), than someone with a "high seizure threshold", (more resistant). The differences in seizure threshold are probably in part due to the natural variations in biochemical and neuranatomical features of the brain. The variations in seizure threshold may predispose one individual to have seizures after a brain injury more easily than another individual.

Provoked Versus Unprovoked Seizures

Under certain conditions, any person or animal can be made to have seizure. These conditions include decrease in oxygen to the brain, low blood glucose, significant alterations in critical electrolytes, such as sodium, potassium, calcium and magnesium, and intoxication with or withdrawal from some substances. Sudden increases in temperature, such as with a fever, can also precipitate seizures. This is particularly true for the "immature brain", in children under five years of age. Seizures occurring under these circumstances, without any other known brain injury or intrinsic cause for seizures, are often called "provoked seizures."

The term "provoked seizure implies that the seizure was a direct result of this transient abnormal, and extreme circumstance and would not be expected to occur spontaneously. An "unprovoked" seizure is one that occurs spontaneously due to either an abnormally irritatible epileptic zone or focus in an area of brain injury or due to an abnormally low seizure threshold.

Febrile Seizures

Fever is a provoking condition for seizures. Benign febrile seizures are seizures occurring with the rise of a fever during an illness without any brain or intracranial infection. Benign febrile seizures occur in children under the age of five years. The seizures is usually a brief, isolated generalized tonic clonic seizure from which the child recovers without any persistent or focal abnormalities. Other seizures may occur during a febrile illness that are not considered as benign. In these cases the seizures may be prolonged, focal, multiple or maybe associated with transient or persistent neurological deficits.

Seizures Type Classification

Breakthroughs in recording seizures and research into causes of seizures have provided valuable information about types of seizures. The International League Against Epilepsy (ILAE) defined and classified various seizure types into a standard system of terminology. These terms helped physicians and researchers communicate more precisely. Older terms that you may have heard, such as "petit mal" seizures and "grand mal" seizures, were frequently misused and have been replaced. The current classification divides seizures into two main types, partial or generalized. A generalized seizure arises on both sides of the brain from the onset while a partial seizure arises from only part of the brain from its onset.

Partial Seizures

A partial seizure arises from an epileptic zone or focus of neurons in a particular part of the brain. Usually, the first symptom of the seizure reflects the function of the brain area in which the focus is located. For instance, if the seizure focus were located in the left sensory cortex in the hand and arm area, a seizure arising from this area may start with unusual sensations in the opposite (right) hand and arm. Clinical information about the first symptoms of a seizure are very important. It helps point to the area in the brain from which the seizures start. For example, if a seizure starts with right hand and arm jerking, then this indicates a focus in the left motor cortex in the hand area.

The electrical discharge that causes the seizure may remain confined to the focus or it may the spread to involve the adjacent areas of the brain, or eventually spread to involve the whole brain. In the cases in which the seizure activity spreads beyond the inciting focus, other clinical manifestations may be seen. For instance, a seizure may start in the left sensory cortex and spread to the left motor cortex. The symptoms would include abnormal sensations on the right side of the body followed by motor activity such as jerking on the right side of the body. Sometimes the spread of the seizure activity extends to both sides of the brain or to centers controlling awareness or consciousness. In that case, the person may lose consciousness or have jerking of both sides of the body.

Simple partial, complex partial and aura

A focal or partial seizure may stay confined to a brain area that does not affect awareness. This is called a "simple partial seizure". A partial seizure in which awareness is effected or consciousness is lost is called a "complex partial seizure". An aura is actually a simple partial seizure with sensory symptoms. The sensory symptoms can be tactile, visual, auditory, olfactory or gustatory. Many persons call these symptoms a "seizure warning", but these are actually part of the seizure.

Partial seizures with secondary generalization

In some cases, a partial seizure starts in focal part of the brain, but the electrical discharge progressively spreads to more areas until both hemispheres are discharging during the seizure. This is called a "partial seizure with secondary generalization". For example, the seizure may start off in the left sensory cortex, spread to the left motor cortex and then spread to both sides of the brain. Clinically, symptoms would follow the pattern and sequence of spread. First there would be sensory symptoms on the right, then motor jerking of the right side of the body, followed by jerking of both sides of the body.

Generalized seizures

A generalized seizure begins on both sides of the brain from the onset. There are several kinds of generalized seizures, absence, tonic, clonic, tonic-clonic, myoclonic, and atonic.

Absence seizures are generalized seizure characterized by a sudden, brief loss of awareness, and abrupt return to awareness. There may be some subtle movements, such as eyelid fluttering during the absence.

Tonic seizure is associated with a rigid stiffening of the body. Clonic seizures are characterized by repetitive jerking. Tonic-clonic seizure is characterized by rigidity followed by jerking.

Myoclonic seizures are characterized by brief rapid "lightening-like" jerks.

Status Epilepticus

Status epilepticus is a condition in which there is a prolonged seizure or multiple seizures without return to one's baseline state. Definitions vary in the length of the seizure, usually it is defined as 15 to 30 minutes. It may also be stated that status epilepticus is present when a seizure is so prolonged or so frequent as to produce a fixed and lasting state. Any seizure type can become sufficiently prolonged to be considered status epilepticus, however it is usually generalized tonic-clonic seizures that are regarded as the most potentially dangerous.

Primary (Idiopathic) and Secondary (Symptomatic) Epilepsies

Primary or idiopathic epilepsies are ones in which there is a genetic predisposition to having a low seizure threshold and spontaneous seizures. There is no other obvious cause or brain injury. Primary or idiopathic epilepsies can be associated with either generalized or partial seizures. Secondary or symptomatic epilepsies are associated with brain injury. The secondary or symptomatic epilepsies can be associated with have either partial or generalized seizures. Diagnosing the syndrome is helpful in predicting the prognosis and treatment.

Epilepsy Syndromes

An epilepsy syndrome may be determined by the seizure type and pattern of seizure occurrence, cause of seizures (etiology), age of onset of seizures, family history of seizures, physical and neurological exam and other factors.

Epilepsy Syndrome Classification

The epilepsy syndrome classification takes several main factors into account. One set of factors is whether the seizures are generalized or partial (focal) in type. Another set of factors is whether the seizure are a result or symptomatic of a known or suspected brain injury (symptomatic or secondary epilepsy), or are inherited (idiopathic or primary) epilepsy. For instance, Childhood Absence Epilepsy is an example of a idiopathic generalized epilepsy. Benign Rolandic Epilepsy is an example of a idiopathic partial epilepsy.

Other Epilepsy Syndromes

Infantile Spasms is an epilepsy syndrome. usually with onset in infancy, characterized by brief and often multiple spasm like body jerks. The accompanying EEG usually shows a distinctive pattern called "hypsarrhythmia" which is a high voltage and chaotic EEG pattern.

Lennox-Gastaut Syndrome is an epileptic syndrome with age of onset in early childhood. It is associated with a static encephalopathy often with mental retardation and is characterized by multiple seizure types which are often refractory to medications.

Diagnostic Tests

Electroencephalogram (EEG)

An electroencephalogram, (EEG), records brain electrical activity, or "brain waves". The EEG is usually recorded from surface electrodes pasted over certain areas of the scalp. The brain activity that is recorded is mainly from the more superficial areas of cortical neurons. Stimulations such as hyperventilation, and intermittent light flashes are usually performed. Recordings can be done with time linked video-EEG monitoring to document and correlate ongoing behavior or seizures with EEG activity. In some cases, an ambulatory unit can be worn around for a day or two allowing for a longer window of opportunity to capture events.

The EEG interpreter or electroencephalographer, evaluates the record for rhythms, and brain wave patterns that should normally be present for the patient's particular age and state ( awake or asleep). The electroencephalographer will also note any disruption in the normal or expected activity and any "dysrrhythmias". Certain patterns are associated with certain brain disorders or seizures. EEG can give information about the location of the seizure focus. The EEG may also show some changes with structural brain injury or with some metabolic or toxic conditions. EEG gives is about electrophysiological function of the brain. The most informative EEG is often one recorded during a suspicious event or seizure. A limitation of EEG is that it only samples that activity occurring during a recording. A recording may not be as informative if a seizure is not captured.

Magnetic Resonance Imaging Scan (MRI)

The MRI of can give rather clear anatomical pictures of the brain. It may be performed with a variety of techniques or with contrast to yield the most information about brain structure. The MRI can not give electrophysiological or brain wave information like the EEG. The two tests are often complementary.

Computerized Axial Topography Scan (CAT)

A CAT scan is a special computerized X-ray that can give an anatomical picture of the brain. A CAT scan can be enhanced by the use of contrast agents and special techniques. CAT scans are limited at times by bone interference . CAT scans are good at showing acute hemorrhages, but may be more limited than the MRI in showing other structural alterations particularly those of deep structures in bony areas.

Antiepilepsy Drugs

An antiepilepsy drug is a medication intended to reduce or eliminates seizures. In general, these medications work to chemically alter the neuronal environment and suppress neuronal firing. Often the drug have effects not only on the brain, but also on other organs.