Cancer is a group of diseases characterized by the uncontrolled growth and spread of abnormal cells. A seizure is a neurological event caused by a sudden, uncontrolled surge of electrical activity within the brain’s nerve cells. The two conditions are linked, and cancer can definitely cause seizures. A seizure may be one of the first noticeable symptoms that prompts medical investigation, sometimes leading to a cancer diagnosis. This neurological event can occur through direct physical invasion of the brain or as an indirect consequence of the cancer’s systemic effects.
When Cancer Invades the Brain
The most direct cause of a seizure is the presence of a tumor within the brain tissue. These tumors can be primary (originating in the brain, such as gliomas) or metastatic (spread from a cancer site elsewhere in the body). The physical mass of the tumor disrupts the delicate electrical balance of the surrounding brain cells, or neurons. This irritation lowers the seizure threshold, making the neurons more likely to fire uncontrollably.
Metastatic brain tumors are a common cause of seizures, especially in patients with lung, breast, or melanoma cancers, which frequently spread to the central nervous system. The tumor mass also causes localized inflammation and swelling, known as peritumoral edema. This combination of mechanical pressure, chemical irritation, and tissue swelling triggers abnormal electrical discharges. Seizures originating from these lesions are often focal, though they can sometimes spread to become generalized.
Systemic Effects and Treatment Complications
Seizures can also be provoked by systemic issues, not just a physical tumor mass in the brain. Metabolic disturbances are a common indirect cause, where the cancer or its complications alter the body’s chemical environment. For instance, hyponatremia (low sodium in the blood) can lead to brain swelling and subsequent seizures. This is frequently seen as a complication of the Syndrome of Inappropriate Antidiuretic Hormone (SIADH) secretion, often associated with small-cell lung cancer.
Conversely, hypercalcemia (elevated calcium levels) resulting from bone destruction due to metastatic disease is another metabolic trigger. Certain chemotherapy agents are directly neurotoxic and can induce seizures. High-dose methotrexate, cytarabine, busulfan, and cisplatin are recognized agents that increase the risk of central nervous system toxicity. Additionally, drugs like vincristine can indirectly cause hyponatremia, contributing to seizure risk.
Paraneoplastic syndromes represent another complex, indirect mechanism involving the body’s immune response. These rare disorders occur when the immune system mistakenly attacks healthy nerve tissue, even if the cancer is located elsewhere. This autoimmune attack causes inflammation and functional disruption that can manifest as persistent seizures.
Identifying the Cause of the Seizure
When a seizure occurs in a patient with known or suspected cancer, a medical investigation is required. The diagnostic process begins with a detailed patient history and a thorough neurological examination to determine the seizure type and potential focus location. This initial assessment guides the selection of advanced diagnostic tools.
Brain imaging is the cornerstone of this investigation, with Magnetic Resonance Imaging (MRI) being the preferred modality. MRI offers superior soft tissue contrast compared to a Computed Tomography (CT) scan, allowing physicians to detect small lesions, tumor characteristics, and subtle surrounding edema. While a CT scan is faster and used in emergencies to rule out acute bleeding, MRI provides the necessary detail to confirm a tumor or metastatic lesion.
An Electroencephalogram (EEG) is also performed to measure the electrical activity of the brain. The EEG confirms the seizure diagnosis and provides clues about its origin by identifying abnormal electrical patterns. In patients with brain tumors, the EEG often shows focal slowing of brain waves, which is typically localized to the area near the lesion. Blood tests are equally important to identify systemic causes, specifically checking for metabolic imbalances like hypercalcemia, hyponatremia, and hypoglycemia.
Treatment Protocols for Seizure Control
The management of cancer-related seizures addresses both the seizure activity and its underlying cause. Anti-epileptic drugs (AEDs) are the primary treatment for controlling electrical instability in the brain. The choice of medication is important in oncology because many older AEDs, such as phenytoin and carbamazepine, are potent inducers of the Cytochrome P450 (CYP450) enzyme system in the liver.
This enzyme induction can accelerate the metabolism of chemotherapy drugs, potentially reducing their effectiveness. Therefore, modern protocols favor non-enzyme-inducing AEDs, with Levetiracetam often being a first-line choice due to its favorable profile and minimal drug interactions. For seizures provoked by systemic issues, correcting the metabolic imbalance, such such as treating hypercalcemia or hyponatremia, is often enough to stop the activity. When brain swelling is the cause, corticosteroids like dexamethasone are used to reduce peritumoral edema, alleviating pressure on the irritated brain tissue.