How Common Are Seizures in Glioblastoma?
Seizures are one of the most disruptive symptoms of glioblastoma. They can arrive without warning and limit your independence. Understanding why they happen and what options help control them is an important early step in your care.
Research reviewed by the Society for Neuro-Oncology estimates that nearly 50% of high-grade glioma patients experience at least one seizure during their illness. For many people, a seizure is the first sign that a brain tumor is present, appearing before imaging is done.
Why Does Glioblastoma Cause Seizures?
Your brain relies on electrical signals between neurons. A seizure happens when neurons fire in an uncontrolled burst that spreads through brain tissue.
Glioblastoma disrupts this system in several ways:
- Glutamate overflow. Glioma cells release excess glutamate, a chemical messenger that excites neurons. Too much glutamate overstimulates nearby neurons and may trigger seizures. The Society for Neuro-Oncology consensus review published in Neuro-Oncology identifies glutamate-induced excitotoxicity as a primary driver of tumor-related seizures.
- Ion channel disruption. Tumor cells alter the flow of sodium, potassium, and chloride across neuron membranes. This destabilizes the chemical balance neurons need to fire in a controlled way.
- Blood-brain barrier breakdown. The tumor erodes the protective barrier between the bloodstream and brain tissue. Proteins and ions leak into the surrounding brain, creating an irritable chemical environment around the tumor.
- Peritumoral edema. Swelling around the tumor compresses nearby brain tissue and lowers the electrical threshold needed to trigger a seizure.
- Tumor location. Tumors close to the cortex, the brain's outer layer that controls movement, sensation, and language, are more likely to cause seizures than tumors in deeper structures.
Your tumor's molecular profile also plays a role. IDH-mutant gliomas have higher seizure rates than IDH-wild-type tumors, which includes most GBMs. To learn how molecular markers affect your treatment, see our guide on molecular tests for newly diagnosed glioblastoma.
Types of Seizures You May Experience
Not all seizures look like the dramatic convulsions shown in movies. Brain tumor seizures often appear in subtler forms that you might not recognize at first.
- Focal aware seizures (also called simple partial seizures): You stay fully conscious but notice unusual sensations. You might smell something strange, feel sudden tingling, have an unexplained rush of emotion, or see involuntary twitching in one limb. These can be the earliest sign that a tumor is irritating nearby brain tissue.
- Focal impaired awareness seizures (complex partial seizures): Consciousness is affected. You may stare blankly, make repetitive hand movements, or feel confused for several minutes afterward. People nearby often notice this before you do.
- Generalized tonic-clonic seizures: The full convulsion with loss of consciousness, muscle rigidity, and rhythmic jerking. These typically last one to three minutes and are followed by fatigue and disorientation.
- Subtle focal seizures: Brief visual changes, feelings like déjà vu, or fleeting sensory disturbances that are easy to dismiss but may be real seizures.
If you experience a new type of seizure or your seizures change in frequency or character, contact your care team. A change in your seizures can signal tumor growth or another problem that needs evaluation.
When Seizures Occur Along the GBM Journey
Seizures can appear at any point. They may be the first symptom before diagnosis, show up during treatment, or return when the tumor grows again. For newly diagnosed patients making many urgent decisions, our overview of what to expect in the first 30 days after GBM diagnosis covers when anti-seizure medications are typically started.
Just after surgery, your brain is inflamed and seizure risk goes up temporarily. As treatment shrinks the tumor, seizures often become less frequent. Medication usually continues throughout treatment to keep seizures controlled.
How Anti-Seizure Medications Work
Anti-seizure medications, also called antiseizure medications (ASMs) or antiepileptic drugs (AEDs), do not treat the tumor. They reduce the chance that abnormal electrical activity will spread and cause a full seizure. Different drugs use different mechanisms:
- Some block sodium channels, stabilizing neurons that would otherwise fire too easily
- Some enhance GABA, the brain's main calming neurotransmitter
- Some bind to the synaptic vesicle protein SV2A, modulating how neurons release excitatory signals
- Some block AMPA receptors, reducing the brain's sensitivity to excess glutamate
The right choice depends on your seizure type, other medications, and kidney and liver function. This decision belongs to a specialist, ideally a neuro-oncologist or a neurologist who specializes in brain tumors.
Why Drug Choice Matters So Much in GBM
This is why specialist involvement is so important in glioblastoma seizure management. A general neurologist may not have the right expertise.
Many older anti-seizure drugs, including phenytoin, carbamazepine, and phenobarbital, are enzyme inducers. They activate liver enzymes that break down many medications, including chemotherapy drugs. When these enzymes are over-activated, chemotherapy drugs like temozolomide may break down too quickly, which reduces how well they work against the tumor.
Research shows that patients on enzyme-inducing anti-epileptic drugs may have lower active concentrations of chemotherapy agents in their bloodstream during treatment. You need seizure control, but not at the cost of weaker chemotherapy.
For this reason, the SNO consensus review recommends non-enzyme-inducing medications for glioma patients receiving chemotherapy. This change has affected how doctors prescribe seizure drugs over the past decade.
Levetiracetam: Today's First-Line Choice
Levetiracetam is now the most common anti-seizure drug for glioma patients. It works by binding to a protein called SV2A, which is different from how older sodium-channel drugs work. It does not interact with liver enzymes that break down other medications.
According to research on the role of levetiracetam in brain tumor seizures, about 70% of patients stopped having seizures on levetiracetam alone, after at least six months. Results vary depending on tumor type and location. It does not interfere with temozolomide or PCV chemotherapy used in glioma treatment.
The most common side effects are irritability, mood changes, and fatigue. Some patients have these side effects. If they happen, tell your care team. They may be able to adjust your dose or switch you to a different medication.
Valproic Acid: Effective but Requires Careful Management
Valproic acid has been used for decades and remains effective for many seizure types. Unlike enzyme inducers, it inhibits certain liver enzymes, which can raise the levels of other drugs in your bloodstream. It must be used carefully with chemotherapy and requires regular blood tests to check liver function and platelet counts.
Research on levetiracetam and valproic acid in glioma shows about 78% of patients stopped having seizures on valproic acid alone within six months. This rate is similar to levetiracetam, though the groups studied were different. It may not be safe for patients with liver disease or those on certain chemotherapy combinations.
Scientists are studying whether valproic acid might kill tumor cells directly because of how it affects histones. This research is still ongoing and is not yet standard treatment. To learn more about this emerging research, see our article on valproic acid and glioblastoma.
Other Anti-Seizure Options
When first-line drugs do not work well or cause bad side effects, your team may try:
- Lacosamide: A newer drug that changes how sodium moves in neurons, with no major interactions with liver enzymes. It may help when combined with levetiracetam for patients whose seizures are not fully controlled.
- Lamotrigine: Works well for focal seizures and does not interact with liver enzymes. It requires a gradual dose increase to reduce the risk of serious skin reactions.
- Perampanel: Blocks AMPA glutamate receptors, which is important because GBM cells release extra glutamate that may cause both seizures and tumor growth. Clinical trials are testing perampanel in high-grade glioma patients. You can find trials at ClinicalTrials.gov.
- Clobazam: A benzodiazepine sometimes added when other drugs do not work.
When Seizures Are Difficult to Control
Drug-resistant epilepsy occurs in about 10 to 15% of GBM patients with seizures. This means seizures that do not stop with two or more properly dosed medications. In lower-grade gliomas, that rate is considerably higher.
When seizures do not respond to medication, your team will check if the tumor is growing, which can restart seizures. They may try combining two or three anti-seizure drugs, consult an epilepsy specialist, or look for clinical trials for glioma seizures. There is no standard guideline for treating hard-to-control glioma seizures, so specialist input is very important.
Does Treating the Tumor Help Seizures?
For many patients, yes. Surgery removes the irritated brain tissue. Radiation shrinks the tumor and kills cells that release excess glutamate. Chemotherapy shrinks the overall tumor burden. Anti-tumor treatments usually help control seizures.
This is why getting good treatment matters. It helps control both the disease and your daily quality of life. If your seizures get worse even though your treatment has not changed, tell your care team. It may signal tumor growth.
Seizure Safety in Daily Life
Medication is the main part of seizure management, but daily habits matter too. The American Brain Tumor Association provides practical guidance on why seizures happen in brain tumor patients and what you can do. Key strategies include:
- Keep a consistent sleep schedule. Sleep deprivation is one of the most reliable seizure triggers.
- Limit or avoid alcohol, which lowers the seizure threshold.
- Never miss a dose. Set a daily alarm as a reminder.
- Keep a seizure log (date, type, duration, time of day, possible trigger) and bring it to every appointment.
- Wear a medical alert bracelet identifying your condition and emergency contacts.
- Share a seizure action plan with family, close friends, and coworkers so they know what to do.
- Avoid bathing or swimming alone. A seizure near water is dangerous.
- Discuss driving with your care team. Most regions require you to be seizure-free for a set period before you can drive.
Prophylactic Medication: Should You Take It Before Any Seizure Occurs?
Newly diagnosed patients often ask this question. Current guidelines do not recommend starting anti-seizure medications if you have never had a seizure. Studies have not shown that preventive medication reduces the risk of a first seizure, and it just adds side effects.
There may be exceptions, especially right after brain surgery when inflammation temporarily raises seizure risk. Your neurosurgeon and neuro-oncologist will guide this decision based on your situation.
When to Talk to Your Doctor
Contact your care team right away if you have your first seizure, if your seizures change, or if side effects are affecting your daily life. Call emergency services immediately for any seizure lasting more than five minutes or for seizures one after another without recovery.
If your medication is not working well, or if you want to know whether your anti-seizure drug affects your tumor, ask your neuro-oncologist. Managing seizures in GBM requires ongoing attention, not just a one-time decision.
This article is for general information and is not a substitute for medical advice. Always consult your oncologist or care team about your specific situation.