A seizure is caused by an abnormal change in the brain’s electrical activity. An event or condition that disrupts the communication between nerve cells, or neurons, in the brain triggers it.
There are many kinds of seizures and many possible causes of seizures, including:
- brain infections
- low blood sugar
Some seizures start in childhood, while others begin in adulthood. These are called adult-onset seizures.
Read on to learn what causes seizures in adults for the first time.
Adult-onset seizures are typically due to a specific condition or traumatic event. This is different than seizures that appear in childhood, which are usually due to idiopathic epilepsy, or related to an unknown cause.
Possible causes of adult-onset seizures include:
Central nervous system infection
Severe central nervous system (CNS) infections caused by bacteria, parasites, or viruses can trigger seizures.
These pathogens cause infection in brain tissue. This can prompt an immune or inflammatory response that leads to abnormal changes in your brain’s electrical activity.
Examples of CNS infections that can lead to seizures include:
- CNS tuberculosis
- viral meningoencephalitis
- meningitis or encephalitis
- brain abscess
- cerebral malaria
- onchocerciasis (river blindness)
- cerebral toxoplasmosis
Adult-onset seizures are often the first sign of a brain tumor. If the seizures recur or get worse, it might mean that the tumor has grown, or caused bleeding or swelling.
Brain tumors that can trigger seizures include:
Different types of tumors cause seizures in different ways, usually due to pressure or bleeding in the brain.
Traumatic brain injury
Another possible cause of a first-time seizure is a traumatic brain injury (TBI).
After a TBI, the seizures may occur immediately. In other cases, they might happen within hours, days, or weeks after the injury. About
More severe injuries are more likely to cause seizures. Other factors that increase your risk of seizures after a TBI include:
- being older than 65
- chronic alcohol use disorder
- injury that penetrates the skull
- contusion, which is a bruise of the brain
- bleeding in the brain
Depending on the injury, a TBI can trigger seizures by causing inflammation or damaging brain tissue. It may also cause seizures by disrupting the way your brain releases neurotransmitters.
Substance use and withdrawal
A first-time seizure in adulthood may be related to the use of certain substances or withdrawal from them.
The most common substances associated with seizures include:
Certain substances can induce seizures by altering neurotransmitter activity. In other cases, a drug may modify electrolytes or blood flow in the brain, resulting in a seizure.
Some substances, like barbiturates, have a sedative effect on the brain. If taken regularly in high doses, suddenly stopping can cause a seizure. Stopping anti-seizure medications or taking them inconsistently can induce a seizure.
Alcohol poisoning and withdrawal
Alcohol poisoning, or an alcohol overdose, is when you drink a large amount of alcohol in a short amount of time. This can cause alterations in your fluid and electrolyte levels, resulting in seizures.
Alcohol withdrawal may also trigger a first-time seizure.
Heavy alcohol use can depress the central nervous system. Suddenly reducing alcohol consumption will affect the nervous system and can cause a seizure.
A stroke occurs when a blood vessel in the brain bursts or becomes blocked. This interrupts blood flow to the brain, which injures the tissue.
The injury can alter the electrical activity in the brain, resulting in a post-stroke seizure. Often, it occurs within 24 hours of the stroke, but a post-stroke seizure can first appear months after a stroke.
The more severe a stroke, the more likely it is to cause a seizure.
There are many types of seizures that can occur in adults. These seizures are sorted into two main categories:
If the abnormal electrical activity begins on one side of the brain, it’s called a focal seizure.
Focal seizures that affect adults include:
- Focal aware seizures. During a focal aware seizure, you don’t completely lose consciousness.
- Focal impaired awareness seizures. This type of seizure causes loss of consciousness.
- Focal to bilateral awareness seizures. This seizure starts in one part of the brain, then spreads to the other side. You might be aware at first, then lose consciousness.
Generalized seizures involve both sides of the brain. They usually cause loss of consciousness.
In adults, the most common types include:
- Generalized tonic-clonic (GTC) seizures. GTC seizures were previously known as grand mal seizures. They make the muscles rigid (tonic phase) and causes muscle jerking (clonic phase).
- Tonic seizures. A tonic seizure causes muscle stiffening, usually in the back, arms, and legs. It doesn’t involve a clonic phase.
- Clonic seizures. During a clonic seizure, your muscles repeatedly jerk.
- Myoclonic seizures. A myoclonic seizure causes jerking in one area of the upper body and limbs.
- Atonic seizures. An atonic seizure, or drop attack, causes sudden loss of muscle tone. You might fall to the floor, or your head might drop.
- Absence seizures. An absence seizure, previously called a petit mal seizure, causes blank staring and slight twitching. You might experience a brief change in consciousness.
- Gelastic and dacrystic seizures. A gelastic seizure causes uncontrollable laughing, while a dacrystic seizure causes uncontrollable crying. These seizures are often associated with a brain lesion called a hypothalamic hamartoma.
- Nonepileptic events. Nonepileptic events, like a migraine attack and fainting, can look like seizures. However, they’re usually caused by psychological and emotional stress instead of abnormal brain activity.
If you think you’re having a seizure for the first time, try to stay calm.
Focus on staying safe and avoiding injury. If possible, move away from furniture and large objects. Lie down on the floor and rest your head on a folded jacket or pillow.
If you’re driving or operating equipment, stop and find a safe area.
It’s possible for an adult without a history of epilepsy to experience a seizure.
Potential causes include central nervous system infections, brain tumors, stroke, and brain injuries. The use or stopping of certain substances, including alcohol, may also trigger a seizure.
The type of seizure depends on the cause. If you have a seizure for the first time, get medical attention as soon as possible. A healthcare professional can help determine the underlying cause and provide a treatment plan, if needed.