What brain condition causes seizures?

Seizures are caused by abnormal electrical activity in the brain. There are many different brain conditions that can lead to recurrent seizures or epilepsy. Some of the most common causes of seizures include:

Traumatic Brain Injury

A traumatic brain injury (TBI) happens when there is a blow or jolt to the head that disrupts normal brain function. TBI can be caused by falls, vehicle accidents, sports injuries, assaults, or explosions. Even a mild TBI or concussion can increase the risk of developing epilepsy later on. About 5% of people with TBI will develop post-traumatic epilepsy within the first 5 years after injury.

How TBI Causes Seizures

TBI causes damage to brain cells and connections between cells. This damage leads to scar tissue formation, inflammation, disrupted neurotransmitters, and changes in neuron excitability. These changes make the brain prone to abnormal electrical discharges that result in seizures.

The part of the brain injured and severity of the TBI impact seizure risk. Moderate to severe TBI has a higher risk of seizures than mild TBI. Injuries involving the frontal and temporal lobes are more likely to cause post-traumatic epilepsy.

Stroke

A stroke occurs when blood and oxygen supply to part of the brain is disrupted. There are two main types of stroke:

  • Ischemic stroke – An artery blockage that causes brain tissue death
  • Hemorrhagic stroke – Bleeding into the brain from a ruptured blood vessel

Stroke damage can lead to scarring, inflammation, and changes in neuron wiring that make the brain prone to seizures. About 5-10% of stroke survivors will develop epilepsy.

How Strokes Cause Seizures

The location and severity of the stroke affects seizure risk. Strokes involving the cortex have a higher risk of seizures than subcortical strokes. Large strokes and strokes causing extensive brain tissue damage also have increased seizure risk. Seizures are more likely to develop within the first year after a stroke.

Brain Tumors

Brain tumors are abnormal growths of cells in the brain. About half of people with brain tumors will experience seizures. The seizure risk depends on the tumor type, size, location, and rate of growth. Fast growing tumors are more likely to cause seizures than slow growing ones.

How Brain Tumors Cause Seizures

Brain tumors can cause seizures through several mechanisms:

  • Pressure and damage to surrounding brain tissue
  • Blockage of cerebrospinal fluid flow causing increased pressure
  • Release of chemical signals that alter neuron excitability
  • Leakage of tumor contents during removal that irritates brain tissue

Low grade tumors like gangliogliomas, low-grade gliomas, and dysembryoplastic neuroepithelial tumors have the highest association with seizures. Temporal lobe tumors often cause complex partial seizures.

Infections

Infections that cause inflammation or damage in the brain can trigger seizures. These include:

  • Meningitis – infection and swelling of the membranes surrounding the brain. About 6% of viral meningitis cases and up to 30% of bacterial meningitis cases have recurrent seizures.
  • Encephalitis – inflammation of the brain itself, often caused by viruses. Seizures occur in about 60% of encephalitis cases.
  • Neurocysticercosis – infection with the pork tapeworm larvae, causing cysts in brain tissue. Seizures develop in 60-90% of symptomatic cases.
  • HIV – Late-stage HIV can cause opportunistic infections, cancers, and damage that leads to seizures.

Infections cause swelling, scarring, and disruption of normal neuron activity. This lowers the seizure threshold. Prompt treatment of the infection can sometimes prevent development of chronic seizures.

Brain Malformations

Abnormal development of the brain in the womb can lead to various malformations. Several types are associated with seizures:

  • Cortical Dysplasia – Localized regions of misorganized cortical tissue. This is the most common cause of intractable childhood epilepsy.
  • Schizencephaly – Abnormal slits or clefts in the cerebral hemispheres.
  • Polymicrogyria – Too many small folds in the cortex.
  • Heterotopias – Nodules of neurons located in the wrong layers of the cortex.
  • Absence of the Septum Pellucidum – A membrane separating brain hemispheres.

These malformations create areas of epileptogenic tissue that generate seizures.

How Malformations Cause Seizures

Malformed brain areas contain abnormal neurons that are hyperconnected and hyperexcitable. They are prone to synchronously firing together to cause seizure activity that then spreads. These regions act as seizure foci that trigger recurrent unprovoked seizures.

Genetic Causes

Many genes have been linked to epilepsy and seizure disorders. Some syndromes tied to genetic mutations include:

  • Dravet syndrome – Severe myoclonic epilepsy beginning in infancy due to SCN1A gene mutation.
  • West syndrome – Infantile spasms, developmental delay, and EEG pattern caused by several possible genes like CDKL5 and ARX.
  • GEFS+ – Generalized epilepsy with febrile seizures plus, linked to SCN1A and SCN2A gene mutations among others.
  • Juvenile myoclonic epilepsy – Seizures beginning in childhood/teen years, involves EFHC1, CLCN2, GABRA1, and other genes.

The genetic mutations involved in these epilepsy syndromes cause ion channel dysfunction, disrupted neurotransmitters, and network connectivity changes that predispose the brain to seizures.

How Genetic Mutations Cause Seizures

Epilepsy genes control development of neuron excitability, signaling between neurons, and network connectivity. Mutations in these crucial genes lower the seizure threshold by:

  • Altering sodium, calcium, potassium, and chloride channels
  • Changing GABA and glutamate neurotransmitter function
  • Disrupting synapses between neurons
  • Causing structural abnormalities

Unknown Cause

About 50% of epilepsy cases have no identifiable cause even after testing. These may be due to subtle brain malformations, microscopic scarring, or genetic mutations that current technology cannot detect. The brain’s wiring, connections, and signaling have lowered seizure threshold for unknown reasons.

How Unknown Cause Epilepsy Develops

Possible explanations for epilepsy of unknown cause include:

  • Very mild congenital brain abnormalities
  • Accumulation of small, undetectable strokes
  • Microscopic scars from infant fevers
  • Spontaneous gene mutations
  • Imbalances in inhibitory and excitatory signaling

Even small disruptions in brain tissue organization, blood flow, or neurotransmitters over time can eventually push networks into generating seizures.

Other Less Common Causes

A few other rare causes of seizures and epilepsy include:

  • Autoimmune epilepsy – The immune system attacks brain proteins causing inflammation.
  • Mitochondrial disorders – Mutations in mitochondria genes impair neuron energy metabolism.
  • Landau-Kleffner syndrome – Childhood disorder where seizures affect language acquisition.
  • Rasmussen’s encephalitis – Progressive inflammation of one brain hemisphere.

These involve damage or disruption to brain cells that disturbs normal signaling and makes seizures more likely.

Triggers vs. Underlying Cause

It’s important to distinguish seizure triggers from the underlying epilepsy cause. Triggering factors like sleep deprivation, drug use, and flashing lights can provoke seizures in someone with epilepsy. But they are not the root cause of the epilepsy itself.

For example, someone with epilepsy from a stroke or head injury may experience more seizures if they drink too much alcohol. But the alcohol exposure does not cause the actual epilepsy – it only triggers seizures in an already susceptible brain.

Types of Seizures

There are many different types of epileptic seizures. The seizures are classified based on where they originate in the brain and how they manifest:

Focal (Partial) Seizures

Focal seizures originate in one area or hemisphere of the brain. They are classified by the symptoms produced:

  • Simple focal seizures – No loss of consciousness, may involve muscle jerks, sensations, or psychic symptoms.
  • Complex focal seizures – Altered consciousness, often with staring, automatisms like lip smacking, unawareness.
  • Secondary generalized seizures – Focal seizure spreads and becomes generalized.

Generalized Seizures

Generalized seizures rapidly engage neurons in both sides of the brain. Types include:

  • Absence seizures – Brief loss of consciousness with staring, most common in children.
  • Tonic seizures – Stiffening of the muscles.
  • Clonic seizures – Repeated jerking movements of the face, arms, legs.
  • Tonic-clonic seizures – Also called grand mal seizures. Stiffening followed by jerking convulsions.
  • Atonic seizures – Loss of muscle tone causing person to collapse or drop objects.
  • Myoclonic seizures – Sudden brief jerking of a body part such as the arm or leg.

Diagnosis

A proper epilepsy diagnosis involves:

  • Medical history – Looking for any possible causes like head injuries, infections, or family history of seizures.
  • Description of the episodes – Documenting seizure signs, symptoms, frequency, and triggers.
  • Neurological exam – Testing reflexes, balance, coordination, and cognitive function.
  • Blood tests – Checking for electrolyte imbalances, genetic mutations, and markers of infections, autoimmunity, or tumors.
  • EEG – Records brain wave activity to detect abnormal discharges.
  • MRI – Provides images of the brain’s structure to look for lesions, scarring, malformations, or tumors.
  • CT scan – Can identify brain abnormalities not seen on MRI.
  • Functional MRI – Maps brain activation during cognitive tasks.
  • PET scan – Metabolic imaging to identify regions of abnormally high or low activity.

Combining the medical history, seizure description, neurological exam, EEG, and brain scans can identify any underlying cause or structural abnormalities provoking the seizures.

Treatments

Epilepsy treatment aims to control seizures and allow the person to live a normal life. Options include:

  • Antiseizure medication – Drugs that suppress abnormal electrical activity, the first line treatment. Types like valproic acid, levetiracetam, carbamazepine, lamotrigine, and phenytoin.
  • Ketogenic diet – High fat, low carbohydrate diet that mimics fasting to reduce seizures.
  • Vagus nerve stimulation – Implanted device that periodically stimulates the vagus nerve.
  • Responsive neurostimulation – Implanted device that detects seizure onset and delivers stimulation to stop it.
  • Surgery – Removal of a seizure focus in cases of localized epilepsy. Like those due to tumor, stroke, or malformation.

Treatment is customized based on the type of seizures, epilepsy cause, age, other health conditions, and lifestyle.

Conclusion

Epilepsy is a complex neurological condition with many possible underlying causes. Anything that disturbs the brain’s delicate electrical signaling can provoke recurrent seizures. Identifying the specific epilepsy cause in a patient allows optimal treatment to control seizures and improve quality of life.

Quick Answers

What are the main causes of epilepsy and seizures?

The main causes include traumatic brain injury, stroke, brain tumors, infections, congenital brain malformations, genetic mutations, and unknown causes where no specific reason is found.

How do these various causes result in recurrent seizures?

All the causes involve some injury, disruption, or dysfunction in groups of brain cells that disturbs normal signaling between neurons. This creates areas prone to abnormal synchronous electrical discharges that spread into seizures.

What are the different seizure types?

Major seizure types include focal seizures starting in one area, and generalized seizures rapidly involving both sides. Specific types are absence, tonic-clonic, myoclonic, atonic, and others defined by their symptoms.

How is the cause of someone’s epilepsy determined?

The cause is identified based on medical history, descriptions of the seizures, neurological exams, blood tests, EEGs to record brain electrical activity, and MRI/CT brain scans to visualize any structural abnormalities.

How are seizures treated?

Treatment involves medications to suppress abnormal electrical activity, devices to stimulate the vagus nerve or deliver responsive neurostimulation, ketogenic diet, and sometimes surgery to remove seizure foci.

Leave a Comment