March 16 - Epilepsy Flashcards
What is a seizure?
A temporary neurological reaction to sudden excessive electrical excitation of cortical neurons (synchronous hyperexcitability of cortical neurons)
Loss of awareness or consciousness, movement or sensation disturbances, changed mood or mental function
Results from either known or idiopathic origins
What is epilepsy?
Chronic neurological disorder affecting the brains
Symptoms are recurrent seizures
Idiopathic: does not have known cause
Individual must have had 2 or more seizures of unknown etiology to be diagnosed with epilepsy
Describe the process of diagnosis
If someone has had only one seizure, you cannot diagnose them with epilepsy at this time. If they have had more than one seizure that was provoked, you must investigate the underlying cause (they might have a seizure disorder, but they don’t have epilepsy). If they have more than one seizure of unknown origin (unprovoked), you must examine the patient history, run diagnostic tests, determine epilepsy syndrome and examine treatment options
What types of diagnostic tests are used to diagnose epilepsy?
Brain imaging
Blood tests
Lumbar puncture (seizure caused by infection or bleeding in the brain)
What types of brain imaging tests are used to diagnose epilepsy?
Electroencephalograph (EEG)
Computerized tomography scanning (CT scan)
Magnetic resonance imaging (MRI)
Positron emission tomography (PET scan)
Why are blood tests run in order to diagnose epilepsy?
Do blood tests to check for infection, anemia, minerals, poisons that may have caused a seizure (secondary causes)
Describe electroencephalography
Non-invasive
Record electrical activity on the brain surface
Locate area of irregularly firing coritcal neurons
Determine severity and type of seizure disorder
Does not diagnose or exclude epilepsy
Person with epilepsy may have normal EEG
Describe an action potential over time (4 steps)
- Resting: membrane potential is -70 mV, there is more Na, Ca and Cl outside the cell and more K inside the cell
- Depolarization: Ca influx creates a partial depolarization. Na channels open and Na rushes into the cortical neuron. The environment inside the cell becomes more positive
- Repolarization: K rushes out of the coritcal neuron, leaving behind a negative charge. Cl rushes into the cortical neuron, bringing a negative charge. The membrane potential repolarizes towards resting state
- Hyperpolarization: Some K channels remain open, which allows K to leak through. The membrane becomes more negative than resting membrane potential
Describe the pathophysiology in the cortical neurons that can lead to a seizure
Clusters of cortical neurons in a localized area simultaneously fire abnormally and this may spread to other regions of the brain.
Initiation: bursts of action potentials (APs) from a cluster of cortical neurons -> synchronization of these neurons -> prolonged neuronal depolarization, leads to repetitive APs -> hyperexcitability due to imbalance of neuronal membrane
Describe the role of aspartate and glutamate
Asp and Glu are excitatory transmitters. When they bind to their respective receptors (AMPA and NMDA), they cause the influx of sodium and calcium into the cell -> internal environment becomes positive -> depolarization -> excitation of the cell
What would be the result a drug that blocks potassium channels?
You risk causing a seizure because you are retaining the positive charge inside the cell
Describe the steps Asp and Glu take to cause depolarization
Asp binds to AMPA receptor, causing the activation of AMPA Increased leak of sodium into the cell Depolarization of the cell Mg2+ plug is dislodged from NMDA Glu can now activate NMDA receptor Sodium and calcium pour into the cell
What does GABA do?
GABA binds to ion channels to allow the influx of chloride ions, causing hyperpolarization (it inhibits the excitation of the cell)
What can cause an imbalanced neuron?
Defective voltage-gated ion channels (causing hyperexcitability; excessive Na or Ca influx, insufficient K efflux or Cl influx)
Excessive excitatory neurotransmitters (NT; glutamate and aspartate)
Insufficient inhibitory NTs (GABA)
Describe the propagation of pathophysiological cortical neurons
Enough excitability to recruit surrounding cortical neurons
Lose surrounding inhibition
Spread of seizure to areas via cortical connections
Describe the termination of pathophysiological cortical neurons
Seizure ends after a few seconds or minutes depending on the type of seizure (99% of the time)
Spontaneous
Unknown mechanism
If there is no termination -> status epilepticus
What are the two types of seizures?
Partial seizures (originates in a localized part of the brain in one hemisphere or a specific lobe) Generalized seizures (occurs in both hemispheres of the brain)
What are the different types of partial seizures?
Simple partial
Complex partial
Secondarily generalized
What are the different types of generalized seizures?
Absence
Atonic
Myoclonic
Tonic-clonic
What happens before a simple partial seizure?
Aura: physiological warning sign before experiencing a seizure (e.g., various scents, anxiousness, deja vu)
What happens during a simple partial seizure?
Symptoms depend on which area of the brain is affected
-motor: e.g., jerking movements, tonic movements (stiffening)
-sensory: e.g., tingling/numbess
-autonomic: e.g., abdominal discomfort
-psychic: e.g., hallucinations, fear, sadness
No loss of consciousness, awake, aware
What happens after a simple partial seizure?
Memory is intact, patient can recall what happened
What happens before a complex partial seizure?
May be preceded by an aura
What happens during a complex partial seizure?
Impaired consciousness (unaware of environment) Involves automatisms (e.g., mumbling, picking at clothing, random walking) May progress into generalized seizure
