A seizure is caused by abnormal electrical activity in the brain. The person having a seizure typically experiences a loss of consciousness, involuntary convulsions, jerking movements or stiffness, and other unusual sensations. Although most people think of these behaviors when they hear the words “seizure” and “epilepsy,” not all seizures involve these symptoms. Sometimes, they are not present at all. Seizures without visible symptoms are called subclinical seizures.
Subclinical seizures do not have any apparent symptoms — this is their defining feature. However, an electroencephalogram (EEG) recorded during a subclinical seizure will show abnormal electrical activity.
Many causes of subclinical seizures have to do with the structure of the brain. Children are particularly at risk of developing this type of seizure. Risk factors for subclinical seizures include:
Some disorders are also associated with subclinical seizures. For instance, children with autism spectrum disorder experience subclinical seizures more frequently than children without autism spectrum disorder.
Older adults can be at risk too. One study showed that 42 percent of patients with Alzheimer’s disease had subclinical seizures compared to only 10.5 percent of patients without Alzheimer’s disease of the same age.
The only way to definitively diagnose subclinical seizures is through EEG monitoring. This diagnostic tool can measure and record electrical activity in the brain through electrodes that are temporarily placed on the head. Because subclinical seizures do not have symptoms besides abnormal EEG activity, taking and analyzing EEG recordings is a necessary part of the diagnostic process. Video-EEG monitoring, when a video camera records a person’s physical activity while they’re being monitored by EEG, can be a useful diagnostic tool. Video-EEG helps physicians match brain activity with the body’s physical movements in real time.
Subclinical seizures are treated similarly to clinical seizures. Antiepileptic drugs (AEDs) are the first line of defense against seizures of all types. Examples of AEDs, or anti-seizure medications, include:
Benzodiazepines such as clonazepam (Klonopin) can also be used to control seizure activity.
Certain lifestyle changes can also help with seizure frequency. These include:
Like all types of seizure disorders, subclinical seizures cannot be cured. However, they can be controlled through treatment.
Aside from medication and lifestyle changes, subclinical seizures can also be treated with epilepsy surgery. One study found that more than 80 percent of individuals with subclinical seizures and auras did not experience focal to bilateral tonic-clonic seizures (previously called complex partial seizures) after temporal lobectomy, a type of brain surgery.
Even though subclinical seizures don’t have physical symptoms, they can still be dangerous. They can be an indicator of other medical and neurologic problems, such as brain abnormalities like tumors.
Subclinical seizures are linked to worse outcomes in babies with congenital heart disease. In one study, babies with heart disease who had heart surgery and experienced subclinical seizures after surgery had greater illness severity and increased mortality (death rate).
Subclinical seizures are also associated with biological changes in the body. One study found that subclinical seizures increased pressure around the brain (intracranial pressure) and metabolic stress. Other research has shown that subclinical seizures can cause long-term anatomical changes in the brain, such as shrinkage of the hippocampus.
A timely diagnosis of subclinical seizures is just as important as a diagnosis of other seizure types. Diagnosis will likely require follow-up with a team of doctors that includes neurologists and other specialists.
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