Brain tumors, whether primary or metastatic, frequently cause seizures by disrupting the brain’s normal electrical stability. A seizure is an uncontrolled, sudden burst of electrical activity that temporarily interferes with normal function. Symptoms range from brief staring spells to full-body convulsions. For many people, a seizure is the first symptom leading to the diagnosis of an underlying brain tumor.
The Mechanism: How Brain Tumors Trigger Seizures
The brain relies on a delicate balance between electrical excitation and inhibition. Tumors interfere with this balance in multiple ways, making the surrounding brain tissue hypersensitive to electrical discharge. When this balance is tipped too far toward excitation, the neurons begin to fire uncontrollably, resulting in a seizure.
One major factor is the physical presence of the tumor, which exerts a mass effect on the surrounding tissue. This mechanical stress distorts and compresses neighboring neurons and their electrical connections. The resulting structural damage can compromise the normal pathways that inhibit electrical activity, making it easier for a neural “short circuit” to occur.
Tumors also create an abnormal chemical environment, often referred to as chemical irritation, that directly irritates nearby healthy brain cells. Tumor cells and responding immune cells release inflammatory mediators and excitotoxic substances. For instance, the tumor microenvironment can feature high levels of the excitatory neurotransmitter glutamate, which lowers the threshold required to trigger an electrical discharge.
Furthermore, the rapidly growing tumor can affect the blood supply and oxygen levels in the surrounding brain, leading to vascular disruption. This change in blood flow and the resulting tissue swelling, known as edema, further contribute to the irritation of neurons. Ultimately, the combination of physical pressure, chemical imbalance, and inflammation transforms normal brain tissue into an epileptogenic, or seizure-generating, zone.
Seizure Types and Prevalence in Brain Cancer
Seizures associated with brain tumors are most commonly focal seizures, meaning the electrical activity begins in a localized area. Symptoms reflect the function of the brain region where the tumor is located. For instance, a tumor in the motor cortex may cause isolated twitching or jerking in one limb. A temporal lobe tumor might cause strange smells, a feeling of déjà vu, or brief, unexplained confusion.
Focal events may sometimes spread across the brain, leading to a generalized seizure. These involve larger areas and often result in a loss of consciousness and full-body convulsions. The initial onset of the seizure is usually traceable back to the tumor site. Because many focal seizures are subtle, they can be easily missed or mistaken for temporary behavioral changes.
The likelihood of experiencing a seizure varies greatly, ranging from under 10% to over 80%. Tumors that grow slowly and are located near the surface of the brain have the highest prevalence, sometimes exceeding 80%. These include low-grade gliomas, gangliogliomas, and dysembryoplastic neuroepithelial tumors (DNETs). High-grade tumors like glioblastomas have a lower incidence, typically around 40-50%. Tumors in the frontal and temporal lobes are significantly more likely to cause seizures than those in the back of the brain.
Distinguishing Tumor-Related Seizures from Other Causes
When a person experiences a new-onset seizure, medical evaluation aims to determine the cause through differential diagnosis. The initial assessment includes a detailed patient history and an account from any witnesses, as the specific symptoms can often point toward the location of the seizure focus. The workup aims to rule out other common causes of seizures, such as metabolic imbalances, infections, stroke, or withdrawal from certain substances.
Neuroimaging is the most important step in identifying a tumor as the underlying cause. A Computed Tomography (CT) scan may be performed first in an emergency setting to quickly check for acute issues like bleeding or a large mass. However, Magnetic Resonance Imaging (MRI) is the preferred and most sensitive tool for detecting subtle structural abnormalities, including small tumors. MRI is essential to distinguish a seizure caused by a tumor from seizures of unknown cause, known as idiopathic epilepsy.
An Electroencephalography (EEG) is routinely used to measure the brain’s electrical activity. While the EEG cannot diagnose a tumor, it helps confirm the event was an epileptic seizure by recording abnormal electrical patterns. The EEG may help localize the area of the brain where the seizure originates, especially when combined with the information from the patient’s symptoms and the MRI.
Management of Tumor-Related Epilepsy
The primary goal in managing tumor-related epilepsy is controlling seizures without interfering with overall cancer therapy. Antiepileptic Drugs (AEDs) are the first line of treatment, stabilizing electrical activity to prevent future seizures. The choice of AED must be carefully considered due to potential drug interactions.
Older AEDs, such as phenytoin or carbamazepine, are enzyme-inducing drugs that accelerate the metabolism of other medications. When used with chemotherapy, these older drugs can clear the cancer treatment too quickly, reducing its effectiveness. Newer AEDs like levetiracetam and lacosamide are preferred because they have minimal interaction with chemotherapy drugs.
The most effective long-term strategy is treating the underlying tumor. Removing the tumor surgically or shrinking it with radiation or chemotherapy eliminates the source of electrical irritation. Successful tumor treatment often significantly reduces or eliminates seizures entirely, restoring electrical stability as the brain tissue heals.