What Is Epilepsy?
Epilepsy is a disorder which occurs due to one or more chronic conditions of the body in which there occurs disturbed nerve cell activity in the brain. This leads to recurrent seizures in a person.
It occurs due to one or more chronic conditions like the brain injury after a road traffic accidentб which leads to disturbing nerve cell activity and uncontrolled no activity in the brain.
It is important to differentiate between the words epilepsy and seizure.
Epilepsy is a condition, which occurs due to excessive and uncontrolled neuronal activity in the brain. This uncontrolled neuronal activity can be generalized or localized to one area of the brain. For example, it can be localized to just the area of the brain, which perceives those touch sensations of the body. Or it can be localized to the area which controls the motor function of the body. It can also be localized to one of the areas like the visual and the auditory perception areas.
The result of the excessive neuronal discharge in one of these areas is called a seizure. The time of the seizure will depend upon the area of the brain that is affected.
Mechanism Of Seizures Development
Now let's talk about the mechanism of seizure development. Normally, there exists a balance between the excitation and inhibition of neurons in the central nervous system including the brain and all the neuronal pathways. This is maintained by chemicals like acetylcholine and GABA.
Seizures developed when a group of neurons in the brain becomes hyperexcitable. This usually happens in two phases.
The first phase is called the initiation phase, in which some neurons due to some reason become hyper excited and start to have excessive neuronal discharges. One of the most important reason is decreased sodium levels in the body called hyponatremia.
The second phase is called the propagation phase. Normally, the neurons, which have neuronal discharges, are surrounded by a zone of inhibitory neurons called the zone of hyper-polarization. This zone of hyper-polarization prevents the spread of excessive neuronal discharges to other parts of the brain.
But due to some abnormality in the brain like decreased sodium levels of the body, the zone of hyper-polarization gets depolarized and the spread of neurons can occur to the other parts of the brain.
This is how the seizure propagates to other parts of the brain after it has been initiated in one region of the brain.
One important term to understand here is epileptogenesis. In the mechanism of seizure development, we took the example of decreased sodium levels in the body called hyponatremia.
Initial event for the seizure can be a more permanent type of injury called brain injury due to road traffic accidents. In this type of brain injury, the neuronal networks become chronically hyper excitable. There is a permanent change in the neuronal networks, which results in spontaneous seizures in the person.
This process, in which a normal neuronal network is converted into a permanent chronic hyper excitable one, is called epileptogenesis.
Types and Classification of seizures and Epilepsy
Seizures are broadly defined into two categories: the generalized and the focal seizures.
The generalized seizures usually start at one place in the brain and then due to widespread neuronal networks spread to the whole of the cerebral cortex. The main characteristic of generalized seizures is their spread of the seizure.
One of the main important structures that helps in the spread is the corpus callosum. Due to this, the seizure spreads to the other hemisphere of the brain.
In comparison, the focal seizures are confined to one area of the brain where they originate, which is usually one hemisphere or a small part of one hemisphere.
Generalized seizures are of many types and one of the most common type of generalized seizures is the generalized tonic-clonic seizures.
In generalized tonic-clonic seizures, there is widespread and uncontrolled neuronal activity in the whole of the cerebral cortex.
As I mentioned, generalized tonic-clonic seizures involve all of the cerebral cortex. There is excessive neuronal discharge in the motor nerves through the brain. Due to this excessive neuronal discharge in the motor nerves, the muscles of the body get contracted without any relaxation. This is called the tonic phase of the generalized tonic-clonic seizure, in which the muscles remain totally contracted.
A tonic phase is characterized by many other symptoms, and one of them is the is ictal cry, which is a typical sound produced by the tonic contractions of the muscles of larynx and exploration.
One of the characteristics of the tonic phase is the impairment of the respiratory drive, which causes the cyanosis in the patient. There is also a tonic contractions of the muscles of the jaw, due to which tongue bites can occur.
In addition to the increased motor activity in the nerves, there is also increased sympathetic discharge from brain, which causes increased heart rate and blood pressure.
The tonic phase usually lasts for 10-20 seconds and then it transforms to the clonic phase. In the clonic phase the continuous discharge from the drain gets interrupted by small durations of relaxation. This occurs because inhibitory mechanisms of the brain come into play and try to control divide spread neuronal activity.
Due to this there occur alternate muscle relaxations and contractions, which cause possum and jerking. This is perceived as violent shaking of muscles.
The clonic phase usually lasts for only one minute and then it transforms into the post-ictal phase.
The postictal phase is characterized by a confusion, unresponsiveness and muscular flaccidity in the patient. The patient usually remains in the postictal phase for one or two hours, after which he gradually transforms into the normal state.
There are other types of generalized seizures, as well, like the generalized tonic and the generalized clonic seizures. These type of seizures are characterized by symptoms of only the tonic and chronic phase respectively without transforming into other states.
One another type of generalized seizure is called the generalized absence seizure. This is very important as it is the most common type of seizure in the children. It is considered due to a genetic abnormality in the children.
Generalized absence seizures are characterized by sudden and brief loss of consciousness in the patients without loss of muscle tone. These seizures usually last only four seconds and there is usually no postictal confusion.
Other type of generalized seizures include atonic seizures and myoclonic seizures.
Like we just discussed, focal seizures usually remain confined to a particular area of the brain. The symptoms of the focal seizures depend upon the site of the brain that is involved and also the spread of the seizure.
If the seizure activity remains confined to the motor area of the brain, the symptoms that are produced are usually the muscle jerking in one area of the body. Some patients also exhibit turning the head to the one side.
If focal seizures occur in the visual cortex of the brain, the symptoms are usually flashes of light, which are only perceived by the patient. Similarly, if the focal seizures occur in the auditory cortex of the brain, the patient perceives the ringing sounds in the ear. If the seizure activity occurs in the sensory area of the brain, it is perceived as sensations or falls touched by the patient.
Focal seizures can also be differentiated into two types:
-focal seizures without this cognitive features;
-focal seizures with discognitive features.
The discognitive features mainly involve the impairment of consciousness.
In the first category, the patient usually does not have any impairment of consciousness. It is fully conscious even during the seizure and a parson is able to interact normally with the surroundings.
This type seizure was previously classified as simple partial seizures.
In the second type of seizures, the patient exhibits marked impairment of consciousness, but not loss of consciousness. The patient appears to be awake but does not interact or answers anyone's questions. The same of seizures were previously classified as complex partial seizures.
Causes of Seizures and Epilepsy
You can easily remember all the causes of epilepsy by remembering a simple mnemonic vitamins D. In this mnemonic V stands for all the vascular causes that are associated with the blood supply of the brain. These include stroke, bleeding and aneurysm.
I stands for infection. Infections, which mainly cause epilepsy, are the meningitis and brain abscesses.
Trauma is one of the leading causes of epilepsy in both young and adult patients. Road traffic accidents and penetrating injuries of the brain come under this section.
Epilepsy can also be a result of autoimmune diseases like CNS, vasculitis and systemically lupus erythematosus.
Various metabolic disorders are a very very common cause of epilepsy and seizures. They include hypoglycemia, hyponatremia and many other metabolic disorders.
Some epilepsy conditions do not have any cause or the cause is unknown. That are considered to be idiopathic epilepsies.
N stands for neoplasms, which includes all the space-occupying lesions of CNS and brain.
From S you can remember all the psychiatric disorders, which lead to epilepsy.
D is a very important category that is drugs. Drugs are a very important cause of epilepsy. Common drugs, which cause seizures, include alcohol, phencyclidine and cocaine.