The broad classification of seizures differentiates true epilepsy—an inherent predisposition toward seizures even in the absence of brain tumors or other transitory causes—from epileptic seizures, a phenomenon caused by transitory changes in the brain’s structure or metabolism, such as those caused by tumors.1 It is important to note that while seizures are a common presenting symptom among patients with brain tumors, the reverse is not true among young patients: most new-onset seizure disorders are not caused by cancer, except in older adults. The likelihood that new-onset seizures are associated with cancer varies by patient age. Among infants and children, seizures usually reflect epilepsy, and only 1% to 3% of new-onset pediatric epilepsy cases involve brain tumors.6 In adults, especially the elderly, seizures are more commonly a presenting symptom of a brain tumor, however.6
Seizure Management Challenges
Managing cancer-associated seizures is a complex and multidisciplinary endeavor. Patients with cancer-associated seizures appear to experience higher rates of adverse events than patients with non-cancer epilepsy, and the possibility also exists for drug-to-drug interactions between antiepileptic medications and chemotherapy agents.1,7,8
Management goals for this patient population are simply stated but not easily achieved: prevent subsequent seizures to avoid their potentially lethal sequelae (including asphyxia) and harms to patients’ quality of life.1 Management requires careful consideration of patient histories and, in some cases, electroencephalograms and cardiologic assessments.1 Determining that seizures are tumor related is based not solely on the neuroimaging determination that a brain tumor is present, but also on exclusion of non-cancer causes such as a history of epilepsy, fainting /syncope, migraine, or non-tumor-associated ischemic stroke.
Treatment of the seizure-causing tumor(s) using resection alone or with radiotherapy, and/or chemotherapy, can help manage tumor-associated seizures.1,3 However, a different therapeutic option may exist.
Role of Antiepileptics Drugs
The role of antiepileptic drugs in managing cancer-associated seizures has been rarely studied in randomized, controlled clinical trials; outcomes from studies of non-cancer epilepsy cannot necessarily be extrapolated to cancer-associated seizures.1 Antiepileptic drug therapy decisions must therefore be based on expert clinician opinion, tolerability, and interactions.1
The long-term use of anticonvulsants as prophylactics against seizures among patients with cancer is controversial and is not widely considered to be justified.3 Some drugs should not be used for seizure control among these patients. Because of the severity of cognitive side effects, for example, the anticonvulsant phenobarbital is not recommended for patients with brain tumors.7 Nevertheless, other antiepileptics are frequently administered to patients with cancer during and around the time of anticancer treatment. Doing so requires careful patient assessment and monitoring, because antiepileptic drugs can have serious side effects, including cognitive deterioration, myelosuppression, liver dysfunction, and skin reactions—incidentally, these reactions appear to be more frequent among patients with brain tumors than other populations.8