Module 14: CNS Drugs Part II Flashcards
Epilepsy
Epilepsy is a neurological disorder that produces brief disturbances in the normal electrical activity in the brain.
Epilepsy is characterized by sudden, brief seizures, the nature and intensity of which vary from person to person.
Seizure
A sudden alteration of behaviour that is caused by CNS dysfunction. Seizures are sudden and transient.
Epileptic Seizure
A seizure that is caused by primary CNS dysfunction. This is due to excess depolarization and hypersynchronization of neurons.
Non-Epileptic Seizure
A seizure-like episode that is not the result of abnormal electrical activity in the brain.
Epilepsy definition
A tendency for recurrent spontaneous epileptic seizures
Status Epilepticus
A single unremitting epileptic seizure of duration longer than 30 minutes OR frequent seizures without recovery of awareness in between. Status epilepticus is an emergency.
Focal/Partial Seizures
These seizures arise in one area of the brain.
The terms focal seizure and partial seizure are interchangeable.
There are two types of focal/partial seizures:
1. Simple partial seizure
2. Complex partial seizure
Simple Partial Seizure
Involve no loss of consciousness.
Symptoms depend on where the seizure activity is arising from.
Example Case
o 45 year old man
o Clonic movements of his right arm
o Progression to right face then right leg
o No impairment of consciousness
o Lasting ~ 45 seconds
o MRI – L motor strip oligodendroglioma
Complex Partial seizure
A complex partial seizure involves loss of consciousness.
Patients may appear to be awake, but are not aware of surroundings.
Symptoms depend again on where the seizure activity is taking place.
Example Case:
- 37 year-old man with right temporal lobe epilepsy.
- Whistling; bicycling movements in left leg.
- Rising epigastric sensation with nausea.
- Normal ictal speech.
- No memory of the events post-ictally (i.e. after seizure).
- Duration: 30 – 45 seconds.
Generalized Seizure
These seizures have a bilateral, diffuse onset, seeming to arise from all areas of the brain at once.
There are 5 different types of generalized seizures:
- Absence seizures
- Tonic/Clonic seizures
- Myoclonic seizures
- Tonic seizures
- Atonic seizures
Absence Seizures
Also called “petit-mal” (an older name).
Involve loss of consciousness, behavioural arrest and staring.
Are usually brief but may occur in clusters and can recur multiple times in a day.
Rarely associated with automatisms (unusual purposeless movements), usually minor if there are any.
More common in childhood.
Tonic/Clonic Seizures
Tonic-clonic seizures involve:
An abrupt loss of consciousness
A tonic period (muscles become rigid), lasting ~ 1 minute
A clonic period (involuntary muscle contractions), lasting and additional 2-3 minutes
Patients may become incontinent and have tongue biting.
In the post-ictal phase patients may be drowsy, confused and frequently complain of headaches.
Used to be called “Grand-mal seizure”
Myoclonic seizures
These seizures involve sudden, brief muscle contractions that can involve any muscle group.
Usually there is no loss of consciousness.
Sometimes they are associated with a later development of generalized tonic-clonic seizures.
Tonic Seizures
Often involve sudden muscle stiffening (rigidity).
Often involve impaired consciousness.
Atonic seizures
Involve sudden loss of muscle tone.
Usually brief, around 15 seconds.
Also known as “drop seizures”, as patients typically drop to the ground.
Potential for falling injuries.
Secondary generalized seizure
A seizure that begins in one area of the brain (like a focal seizure) and then spreads throughout the brain.
The preliminary focal phase is sometimes referred to as an “aura”.
Localizing Focal Seizures
The location of a focal seizure can be determined by evaluating the patient’s symptoms and what we know about the various regions of the brain
Frontal Lobe
Simple repetitive motor movements involving a localized muscle group are associated with seizure activity in the contralateral (opposite side of the brain) primary motor cortex.
Tonic posturing affecting the entire side of the body are associated with seizure activity in the contralateral Supplemental Motor Area (SMA) and other higher level motor structures.
Very complex behavioural automatisms that involve bilateral movement such as swimming or bicycle riding movements are associated with seizure activity in higher areas of the frontal cortex. These behaviours often involve vocalizations, laughter and/or crying.
Temporal Lobe
Emotions such as anger, fear, euphoria and psychic symptoms such as déjà vu, jamais vu or amnesia are associated with seizure activity in the temporal lobe.
Auditory (hearing) hallucinations of buzzing or voices talking, and olfactory (smell) and gustatory (taste) hallucinations are associated with the temporal lobe.
More complex sensory phenomena, involving visual distortions, paresthesias (i.e. numbness) and autonomic disturbances can also be associated with temporal lobe seizures.
Parietal Lobe
Localized paresthesias, such as numbness and “pins and needles”, are associated with seizure activity in the contralateral somatosensory cortex.
More complex and widespread paresthesias are associated with seizure activity in the somatosensory association cortex.
Seizure activity in the higher order sensory association areas in the parietal lobe can be associated with complex multi-sensory hallucinations and illusions. Can be hard to distinguish from temporal lobe seizure activity, which is more common.
Occipital Lobe
Visual hallucinations, such as flashing or a repeated pattern in the environment, are associated with seizure activity in the occipital lobe. The hallucinations are less likely to be of organized objects such as people or faces.
Seizure activity in the occipital lobe can also produce temporary blindness or decreased vision, as well as the sensation of eye movement. Patients may have reflex nystagmus (involuntary eye movement).
Simple partial seizures in the occipital lobe can be mistaken for migraine headaches, as many of the symptoms are similar to common migraine auras.
Epileptogenesis
There are three main classifications for the etiology of epilepsy:
- Symptomatic epilepsy - Epilepsy arising from an identified physical cause, such as a brain tumor, stroke, infection, or other injury.
- Idiopathic Epilepsy - Epilepsy that does not have an identifiable cause; there is often a family history of seizures, and genetics likely play a role.
- Cryptogenic epilepsy - Epilepsy that is likely to have an underlying cause that has not been identified.
The Seizure Threshold
Seizures are caused by spontaneous, uncontrollable discharges from hyperexcitable areas of the brain.
The seizure threshold can be thought of as the balance between excitable and inhibitory forces in the brain.
Everybody has a seizure threshold and the seizure threshold affects how susceptible a patient is to having a seizure.
Keep in mind that seizures are mediated by changes in electrical activity, so the ability to reach threshold and fire an action potential is important in the generation of a seizure.
Some factors that may affect the seizure threshold are: stroke, head injury, drug/alcohol withdrawal, infection, tumour, severe fever, visual stimuli (flashing lights).
Antiepileptic Drugs (AED’S)
Antiepileptic drugs work by four distinct mechanisms of action:
- Blocking sodium channels.
- Blocking voltage-dependent calcium channels.
- Glutamate antagonists
- Potentiating the actions of GABA.