A subclinical seizure is a type of seizure that occurs with few noticeable physical symptoms. Potential symptoms may be subtle and include blinking or staring into space.
Unlike typical seizures, doctors can only diagnose subclinical seizures through diagnostic tests like an electroencephalogram (EEG), which measures abnormal brain activity.
While there may be minimal outward signs, these seizures indicate atypical electrical activity in the brain and may still have implications for neurological health.
Subclinical seizures typically do not present with the noticeable symptoms that most people associate with clinical seizures, such as convulsions or loss of consciousness.
Symptoms can be vague or absent. This means that people may not be aware of subclinical seizures until a doctor confirms them using diagnostic tools like EEGs.
Subclinical seizures may include the following types of seizure activity:
- an absence seizure, also known as a generalized nonmotor seizure or petit mal seizure, which can happen when someone is awake and appears to be alert
- seizures during sleep that do not involve convulsions
- seizures that do not involve convulsions in people with conditions that affect cognition, such as:
- dementia
- schizophrenia
- severe depression
- catatonia
- seizure activity with no or minimal movements in people who are unconscious, such as people with encephalitis or who have experienced cardiac arrest or severe respiratory distress
According to a 2022 retrospective study, subclinical seizures may occur among people who develop epilepsy at an early age.
Underlying conditions that disrupt typical brain function may also cause subclinical seizures. For example, a
- acute brain injury
- epilepsy
- congenital brain defects
- stroke
- hypoxic-ischemic encephalopathy, in which the brain does not get enough oxygen
According to the 2022 study, the overall prevalence of subclinical seizures is unclear. However, research suggests subclinical seizures are more common in:
- children with epilepsy
- people with epilepsy that is resistant to medical management
- people with frequent clinical seizures
The researchers also highlight that reported prevalence statistics may vary depending on the type and length of EEG recordings. For example, the sensitivity using intracranial EEG recordings is higher than on scalp EEG recordings.
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A 2021 long-term study suggests that subclinical seizure activity may occur in around 50% of people with Alzheimer’s disease who have never had a clinical epileptic seizure.
The major difference between clinical and subclinical seizures lies in the visible physical symptoms.
The symptoms associated with clinical seizures may be easier to detect without special diagnostic tools, although confirmation is typically necessary using tests such as an EEG or MRI.
Both clinical and subclinical seizures can cause a person to lose awareness. In both types, a person may experience confusion or altered sensations.
During a subclinical seizure, people may display a lack of interaction. Clinical seizures may present with more obvious symptoms, such as severe convulsions.
Despite the absence of convulsive symptoms, subclinical seizures occur due to seizure activity in the brain and may require treatment to prevent potential complications.
Treatment options may depend on the underlying cause of the seizures and the frequency with which they occur. For example, if the seizures are due to temporal lobe epilepsy, healthcare professionals will use anti-epilepsy drugs that are indicated for that type of epilepsy.
When subclinical seizures occur in infants, doctors may treat with anticonvulsant medications to reduce brain injury and inflammation.
A 2022 article suggests that surgical treatment of the subclinical seizure onset zone may have favorable outcomes. The researchers included various types of surgery in this treatment bracket, including resection, stimulation, and laser interstitial thermal therapy.
According to a 2023 article, healthcare professionals may treat subclinical seizures less aggressively than clinical seizures. However, the treatment depends on the specific type of subclinical seizure and its anticipated outlook.
In people with persistent subclinical seizures, continuous EEG monitoring also be necessary
The long-term outlook for someone with subclinical seizures may depend on the
In some cases, subclinical seizures may persist even after a doctor effectively treats clinical seizures.
According to a 2022 retrospective study, subclinical seizures may also lead to irreversible damage to a person’s brain function. For example, they may contribute to a faster cognitive decline in people with Alzheimer’s disease.
The study researchers suggest that prompt management may be beneficial to outcomes.
People should
However, subclinical seizures usually cause less obvious symptoms, and people usually aren’t aware of their own seizures. Family members, friends, or coworkers may be unaware the person is having a subclinical seizure and may mistake them as distracted or daydreaming.
Subclinical seizures may occur in people with conditions that affect typical brain function, such as epilepsy, Alzheimer’s disease, and brain injuries. Anyone with one of these conditions or factors should regularly communicate with their healthcare team.
Caregivers may also be able to watch for atypical behaviors in children with developmental disorders and adults with neurodegenerative diseases and report anything unusual to a doctor.
A subclinical seizure refers to a seizure that occurs without obvious physical symptoms, meaning it does not produce the typical signs people associate with seizures, such as convulsions or loss of consciousness.
Healthcare professionals can only confirm this type of seizure through diagnostic tools like an EEG. People may miss them because they do not manifest externally, but these seizures may still indicate atypical brain function.
Doctors may choose to treat subclinical seizures with anticonvulsant medications or surgery. They will also aim to treat or manage any underlying conditions that may be causing the seizure activity.
