Epilepsy Flashcards
What is Epilepsy?
Epilepsy is a broad term that includes a group of neurological disorders characterized by epileptic seizures.
- Affects 0.5% - 2.0% of the general population;
- Epilepsy is more a symptom of several diseases, than a disease itself;
- Defined by the occurrence of at least one epileptic seizure, but characterized by recurrent seizures.
Action potentials (electrical activity) are the foundation to a functional nervous system. In the case of epilepsy, these well-timed, highly controlled action potentials get out of control. - Storm of discordant activity in the brain.
Epileptic seizures
Epileptic seizures are defined as a brief episode of abnormally excessive cortical neuronal activity.
- Sudden, excessive local discharges within the brain’s gray matter;
- Range from brief, undetectable seizures to prolonged, vigorous shaking;
- Associated with variety of physical injuries (e.g. broken bones);
Wilder Penfield once wrote (1941):
- “Seizures are older than humans”;
- “Trephined skulls excavated from the caves of the Neolithic period are probably evidence of early humans’ attempt to release the demons thought to be responsible for epilepsy”
Epilepsy & Stigma
There was a time when epilepsy was highly stigmatized.
Physicians were very careful about using the word, and “labeling” patients;
People thought epilepsy was contagious, via “evil breathe” and would avoid epileptic patients (would spit at them, refuse to eat around them, etc.);
Until 1956, people with epilepsy could not marry in 17 states of the United States!
Epileptic patients were segregated from the rest of the population for religious matters deemed possessed.
In ancient religious tradition, seizures were considered a punishment by God, or the work of demons.
Hippocrates noted that head injuries to soldiers and gladiators lead to seizures;
Concluded there must be a physical cause.
Types of Epileptic Seizures
Generalized seizure
Partial seizure
In both cases, neurons within affected area fire with a synchrony that never occurs during normal behavior.
Generalized seizure
- Widespread;
- Involves activation of entire cerebral cortex of both hemispheres;
- In many cases they grow from a focus, but point of origin is not always known.
Generalized Seizures typically have no apparent local onset;
Tonic-clonic (grand mal) most severe;
Absence (petit mal) unresponsive, blinking repeatedly;
Atonic (loss of muscle tone; temporary paralysis).
Partial seizure
- Definite focus or source of irritation;
- Involves only a small, circumscribed area of the cortex;
- Typically begin in specific area of the motor or sensory cortexàclonic movement of part of a limb vs. abnormal sensations (aura), respectively.
- Simple vs. Complex.
Partial Seizures (aka focal seizures)
Simple (no major change in consciousness)
Localized motor seizure
Motor seizure with progression of movements as seizure spreads along the primary motor cortex;
Sensory (somatosensory, visual, auditory, olfactory, vestibular)
Psychic (forced thinking, fear, anger, etc.)
Autonomic (e.g. sweating, salivating, lip smacking/chewing, etc.)
Complex (with altered consciousness)Includes subtypes 1 – 5 above.
Partial Seizures Generalized Cortical Seizures
Simple or complex partial seizures that evolve to generalized cortical seizures (grand mal).
Grand Mal Seizures
Tonic phase and Clonic phase
Grand Mal Seizures Tonic phase
Tonic phase
- Beginning of a grand mal seizure;
- Muscles contract forcefully;
- Patient is fully unconscious;
- Rigid posture is sustained for ~15 seconds.
Grand Mal Seizures Clonic phase
Clonic phase
- Muscles begin trembling, then start jerking convulsively;
- Muscles move quickly at first, then more and more slowly;
- Eyes roll into back of head;
- Face is contorted, tongue may be bitten (off);
- Intense activation of autonomic nervous system (sweating, salivating);
- After ~30 seconds, muscles relax and patient resumes breathing.
Clinical Symptoms of Epilepsy
The clinical symptoms/behavioral features of a seizure are entirely dependent on the population of neurons involved.
Most generalized seizures include activity from virtually all cortical neurons.
- Consciousness is lost;
- All muscle groups may be activated.
Convulsions occur if the abnormal activity involves the motor cortex.
- Wild, uncontrollable activity of muscles.
Tonic (ongoing) activity vs. Clonic (rhythmic) patterns.
Jacksonian March
Jacksonian Epilepsy (i.e. partial/focal seizures) begin in one specific part of the brain (foci) and spread through adjacent parts of the brain.
Jacksonian March
- Electrical activity is slowly marching across the motor (or sensory) cortex;
- Orderly, sequential progression of clonic movements in a seizure;
- Typically begins with foot, hand or face;
- Electrical impulses travel from foci to adjacent regions of the cortexàbody parts will be activated by these cortical regions.
Auras
Often grand mal seizures are preceded by changes in mood, abnormal motor movements, or other sensory anomaliesàreferred to as auras.
Auras are a preview or transient sensory event that typically occurs before the onset of a seizure.
- Nature of aura varies according to the location of the focus.
K-9’s have the ability to sense auras and alert the necessary help to avoid damage to an epileptic patient.
- Minutes, sometimes hours before onset of seizure; - Changes in human behavior, scent, etc.;
- No scientific evidence to explain this mechanism.
What Causes Epilepsy?
Cause of most cases of epilepsy is largely unknown.
There are many factors that have been associated with development of epilepsy:
- Brain injury (scarring); - Stroke;
- Brain tumors;
- Neuro-trauma;
- Neuro-infections;
- Birth defects/genetic abnormalities.
Epileptic seizures are the result of abnormal, excessive neuronal activity in the brain.
- Typically activity in the cortex, however can originate or spread to sub-cortical regions.
epileptogenic
Certain environmental factors have been shown to be
epileptogenic (arrow) to generate epilepsy.
- Flashing lights can trigger reflexive epilepsy;
- Infections causing high fevers can produce seizure.
One of the most common causes of seizures is scarring, which may be produced by injury.
- Scarring irritates the brain tissue surrounding it, causing an increase in neural activity;
- Typically patients who experience brain trauma don’t show seizures for considerable amounts of time;
- Between seizures, surrounding inhibitory neurons increase activity as a compensatory mechanism.
Kindling
It is likely that the atypical neuronal activity seen in epilepsy generates plastic changes in cortical circuitry.
- Plastic changes are critical for pathogenesis of the disease;
- Strength of communication at synapse changes.
Kindling is a commonly used model for the development of seizures and epilepsy, in which the duration and behavioral involvement of induced seizures increases after seizures are induced repeatedly.
- Stimulating electrode is placed in the brain (e.g. amygdala);
- Weak electrical stimulation is applied à no discernable effect on behavior is observed;
- As weak stimulation is repeated once a day for several weeks, it begins to produce behavioral and electrical indications of a seizures;
- Over time, the weak stimulation causes full-blown grand-mal seizures.
The effects of kindling are more-or-less permanent;
- Years later, the same weak stimulus leads to full blown seizure;
- Weak stimulation produces long-lasting changes in the excitability of the brain that time cannot reverse.
