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Subclinical Seizures: Symptoms, Causes, and Treatments

Posted on August 18, 2022
Medically reviewed by
Evelyn O. Berman, M.D.
Article written by
Brooke Dulka, Ph.D.

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.

Symptoms of 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.

Causes and Risk Factors for Subclinical Seizures

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:

  • Traumatic brain injury
  • Stroke
  • Brain tumor
  • Infection of the brain, such as meningitis or encephalitis
  • Oxygen deprivation at birth (hypoxia)

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.

Diagnosing Subclinical Seizures

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.

Treatment Options for Subclinical Seizures

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:

  • Being on a ketogenic (high-fat, low-carbohydrate) diet
  • Getting adequate sleep
  • Reducing stress levels
  • Avoiding seizure triggers, such as strobing lights

Prognosis of Subclinical Seizures

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.

Building a Community

When you join MyEpilepsyTeam, you gain a social support network of more than 109,000 people who understand what it’s like to live with seizures, including subclinical seizures.

Do you or a loved one experience subclinical seizures? Have you found ways to manage them? Comment below or post on MyEpilepsyTeam.

References
  1. Subclinical Seizures — Cedars Sinai
  2. Detection of Electrographic Seizures With Continuous EEG Monitoring in Critically Ill Patients — Neurology
  3. Incidence of Seizures on Continuous EEG Monitoring Following Traumatic Brain Injury in Children — Journal of Neurosurgery
  4. Neonatal Posterior Cerebral Artery Stroke: Clinical Presentation, MRI Findings, and Outcome — Developmental Medicine & Child Neurology
  5. Nonconvulsive Status Epilepticus in Patients With Brain Tumors — Seizure
  6. Prognostic Value of EEG in Neonatal Meningitis: Retrospective Study of 29 Infants — Pediatric Neurology
  7. Electroencephalographic Characteristics of Epileptic Seizures in Preterm Neonates — Clinical Neurophysiology
  8. Prevalence, Significance, and Clinical Characteristics of Seizures, Epilepsy, and Subclinical Electrical Activity in Autism — The North American Journal of Medicine and Science
  9. Incidence and Impact of Subclinical Epileptiform Activity in Alzheimer’s Disease — Annals of Neurology
  10. Summary of Antiepileptic Drugs — Epilepsy Foundation
  11. Auras and Subclinical Seizures: Characteristics and Prognostic Significance — Annals of Neurology
  12. Subclinical Seizures Identified by Postoperative Electroencephalographic Monitoring Are Common After Neonatal Cardiac Surgery — The Journal of Thoracic and Cardiovascular Surgery
  13. Pericontusional Brain Tissue Exhibits Persistent Elevation of Lactate/Pyruvate Ratio Independent of Cerebral Perfusion Pressure — Critical Care Medicine
  14. Nonconvulsive Seizures After Traumatic Brain Injury Are Associated With Hippocampal Atrophy — Neurology

All updates must be accompanied by text or a picture.
Evelyn O. Berman, M.D. is a neurology and pediatric specialist and treats disorders of the brain in children. Review provided by VeriMed Healthcare Network. Learn more about her here.
Brooke Dulka, Ph.D. is a freelance science writer and editor. She received her doctoral training in biological psychology at the University of Tennessee. Learn more about her here.

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