Epilepsy is a group of neurological diseases characterized by recurrent seizures. Seizures happen as a result of a sudden surge in the brain’s electrical activities. Depending on which part of the brain is affected, a seizure may manifest as loss of awareness, unusual behaviors or sensations, uncontrollable movements or loss of consciousness.
The brain is a complex network of billions of neurons. Neurons can be excitatory or inhibitory. Excitatory neurons stimulate others to fire action potentials and transmit electrical messages, while inhibitory neurons SUPPRESS this process, preventing EXCESSIVE firing.
A balance between excitation and inhibition is essential for normal brain functions. In epilepsy, there is an UP-regulation of excitation and/or DOWN-regulation of inhibition, causing lots of neurons to fire SYNCHRONOUSLY at the same time. If this abnormal electrical surge happens within a limited area of the brain, it causes PARTIAL or FOCAL seizures.
If the entire brain is involved, GENERALIZED seizures will result. Partial seizures subdivide further to: - Simple partial: depending on the affected brain area, patients may have unusual feelings, strange sensations or uncontrollable jerky movements, but remain conscious and aware of the surroundings. - Complex partial seizure on the other hand involves a loss or changes in consciousness, awareness and responsiveness.
Generalized seizures subdivide further to: - Absence seizures: this type occurs most often in children and is characterized by a very brief loss of awareness, commonly manifested as a blank stare with or without subtle body movements such as lip smacking or eye blinking. People with absence seizures may not be aware that something is wrong for years. Kids who start having absence seizures in early childhood stand a good chance of outgrow them without treatment.
- Tonic seizures are associated with stiffening of muscles, or INCREASED muscle tone, and may cause the person to fall, often backwards. - Atonic seizures, also known as drop attacks, on the other hand, are characterized by a sudden LOSS of muscle tone, which may cause the person to collapse or drop down. - Clonic seizures are associated with RHYTHMIC jerking muscle movements.
Most commonly affected are the muscles of the neck, face, arms and legs. - Myoclonic seizures are sudden brief jerks or twitches of muscles. Patients typically react as if hit by a jolt of electricity.
- The most dramatic are tonic-clonic seizures, also known as convulsive seizures. These are combinations of muscle stiffening and jerking. This type is what most people relate to when they think of a seizure.
It also involves sudden loss of consciousness and sometimes loss of bladder control. A tonic-clonic seizure that lasts longer than 5min requires immediate medical treatment. Epilepsy may develop as a result of a brain injury, tumor, stroke, previous infection or a birth defect.
Generalized seizures that start in childhood are likely to involve genetic factors. Epilepsy due to a single gene mutation is rare. More often, an interaction of multiple genes and environmental factors is responsible.
Hundreds genes have been implicated. Examples include genes encoding for GABA receptors – major components of the inhibitory circuit, and ion channels. Many genetic disorders that cause brain abnormalities or metabolic conditions have epilepsy as a primary symptom.
The cause of epilepsy is unknown in about half of cases. Diagnosis is based on observation of symptoms, medical history, and an electroencephalogram, or EEG, to look for abnormal brain waves. An EEG may also help in differentiating between partial and generalized seizures.
Genetic testing maybe helpful when genetic factors are suspected. There is no cure for epilepsy but various treatments are available to control seizures. Medication successfully controls seizures for about 70% of cases.
Many anti-epileptic drugs are available which target sodium channels, GABA receptors, and other components involved in neuronal transmission. Different medicines help with different types of seizures. Patients may need to try several drugs to find the most suitable.
Dietary therapy: ketogenic diet has been shown to reduce or prevent seizures in many children who do not respond to medication. Ketogenic diet is a special high-fat, low-carbohydrate diet that must be prescribed and followed strictly. With this diet, the body uses fat as the major source of energy instead of carbohydrates.
The reason why this helps control epilepsy is unclear. Nerve stimulation therapies such as vagus nerve stimulation in which a device placed under the skin is programmed to stimulate the vagus nerve at a certain rate. The device acts as a pacemaker for the brain.
The underlying mechanism is poorly understood but it has been shown to reduce seizures significantly. Finally, a surgery may be performed to remove part of the brain that causes seizure. This is usually done when tests show that seizures are originated from a small area that does not have any vital function.
