Brain tumors can definitively cause seizures. A seizure is an abnormal, uncontrolled electrical discharge among the brain’s nerve cells. This electrical misfiring temporarily disrupts the brain’s normal messaging, leading to various physical and sensory effects. Seizures are a frequent symptom associated with brain tumors, often being the first sign that prompts a medical diagnosis.
How Tumors Disrupt Brain Electrical Activity
Brain tumors trigger seizures through a combination of physical effects and complex chemical alterations within the surrounding brain tissue. As a tumor grows, it acts as a space-occupying lesion, directly compressing or distorting the healthy neurons around it. This physical pressure alone can irritate the nerve cells, causing them to fire erratically instead of maintaining their normal, regulated electrical rhythm.
The tumor also causes swelling, known as peritumoral edema, which further contributes to a reduced seizure threshold. This swelling changes the local environment, creating mechanical stress on the neural networks. Furthermore, the tumor cells actively release metabolic byproducts and inflammatory substances that interfere with normal neuronal signaling.
One of the most profound chemical changes involves the excitatory neurotransmitter glutamate. Brain tumors, particularly gliomas, can release toxic levels of glutamate, which overstimulates nearby neurons and makes them hyper-excitable. Star-shaped brain cells called astrocytes usually help to clear excess glutamate, but the tumor can impair this function, allowing the excitatory chemical to accumulate and trigger uncontrolled electrical activity.
Types of Seizures Caused by Brain Tumors
Since a brain tumor is a localized mass, the resulting seizures often begin in a specific area, classifying them as focal onset seizures. The presentation varies widely depending on the tumor’s exact location and the brain function being disrupted. A focal seizure can manifest as a simple motor symptom, such as isolated twitching of a finger or limb, while the person remains fully aware.
Other focal onset seizures can involve sensory or psychological disturbances, such as experiencing a strange smell or taste, or a sudden, intense feeling of déjà vu. If the abnormal electrical activity affects a slightly larger area, the person may experience impaired awareness, appearing confused or unaware of their surroundings during the event. These seizures may involve repetitive, non-purposeful movements like lip-smacking or picking at clothes.
The localized electrical disturbance of a focal seizure may eventually spread across the entire brain, resulting in a focal to bilateral tonic-clonic seizure. This event, previously known as a secondary generalized seizure, leads to a loss of consciousness and the full-body convulsions often associated with a seizure. Although less common in tumor patients than focal seizures, this spread of electrical activity can happen rapidly.
Tumor Location and Seizure Risk
The likelihood of a brain tumor causing a seizure is influenced by its location. Tumors that grow near the brain’s surface, in the cerebral cortex, are more likely to generate seizures than those located in deeper brain structures. The cortex has a naturally high level of electrical excitability.
Specifically, tumors located in the frontal and temporal lobes carry the highest risk of seizure generation. The temporal lobe, in particular, is an area highly sensitive to irritation and frequently involved in seizure activity. Conversely, tumors situated in the occipital lobe are associated with a lower propensity for causing seizures.
The rate of tumor growth also plays a counterintuitive role in seizure risk. Slower-growing, low-grade gliomas, such as oligodendrogliomas and grade II astrocytomas, are more likely to cause seizures than rapidly-growing, high-grade tumors like glioblastoma. Seizures are reported in up to 60-85% of patients with low-grade gliomas, compared to a lower incidence of 25-60% in high-grade tumors. This increased rate may be due to the slow growth allowing time for surrounding brain tissue to adapt and become chronically irritated.
Controlling Seizures Associated with Brain Tumors
The management of seizures in patients with brain tumors involves a dual approach focusing on symptom control and treatment of the underlying cause. Anti-seizure medications (ASMs) are the primary method used to control the electrical instability. These medications regulate the abnormal firing of neurons and reduce the frequency and severity of seizure events.
Selection of a specific ASM is carefully considered due to potential interactions with other cancer treatments, like chemotherapy. For instance, levetiracetam is often a preferred first-line agent because it has fewer drug-to-drug interactions and is generally well-tolerated. If monotherapy with one drug is not sufficient, a second ASM may be added to achieve optimal seizure control.
Treating the tumor itself is one of the most effective ways to manage the associated seizures. Surgical removal of the tumor is associated with a reduction in seizure frequency, as it alleviates the physical mass effect and removes the source of chemical irritation. Chemotherapy and radiation therapy can also contribute to seizure control by shrinking the tumor mass and reducing the surrounding edema.