Immunotherapy and Seizures: What You Should Know

Immunotherapy can, in rare cases, be linked to neurological side effects such as brain inflammation (encephalitis), which may include seizures. ^[1] Some immunotherapy drugs list seizures as a serious adverse event that may require stopping treatment. ^{[2] [3]} Immune checkpoint inhibitors can cause a spectrum of neurologic immune-related events, and severe cases have been reported, sometimes including seizures. ^[4] In very uncommon situations, checkpoint inhibitors like nivolumab have been associated with severe brain toxicity that presented with seizures. ^[5] Seizures are also a recognized part of neurotoxicity with immune effector cell therapies (like CAR T cells), where they are included in formal grading criteria. ^{[6] [7]}

How often does this happen?

Most people on immunotherapy do not experience seizures, but neurologic immune-related adverse events do occur in a small percentage, with higher risk when certain therapies are combined. ^[8] Neurological toxicities with checkpoint inhibitors are considered infrequent but potentially serious, including meningitis, encephalitis, and neuropathies. ^{[9] [10]} CAR T–related neurotoxicity (ICANS) more commonly includes confusion, language problems, and sometimes seizures. ^{[11] [12]}

Why can immunotherapy trigger seizures?

• Immune activation can inflame the brain or its coverings (encephalitis or meningitis), lowering the seizure threshold. ^[1]
• Some agents have direct or indirect neurotoxic profiles where seizures are listed among serious adverse events. ^{[2] [3]}
• CAR T–related inflammatory cascades and blood–brain barrier changes contribute to neurotoxicity and seizures. ^{[13] [14]}

Warning signs to act on

• New or worsening headaches, fever, confusion, memory changes, hallucinations, neck stiffness, or extreme sensitivity to light can be clues to brain inflammation. ^[1]
• Persistent dizziness, behavior changes, or focal neurologic deficits (like weakness or speech trouble) deserve urgent attention. ^[15]
• Any first-time seizure or recurrent seizures needs emergency evaluation. ^[7]

What to do immediately if a seizure occurs

• Ensure safety: protect from injury, turn the person on their side, time the event, and avoid putting anything in the mouth.
• Call emergency services if a seizure lasts more than 5 minutes, repeats without full recovery, or if there is trouble breathing. ^[7]
• Inform the oncology team promptly, as some therapies may need to be paused and urgent work-up is needed. ^{[2] [3]}

Medical evaluation and treatment

• Clinicians will typically check labs, perform brain imaging, and may use EEG to look for ongoing electrical seizures. ^[7]
• If immune-related brain inflammation is suspected, corticosteroids are commonly used to calm the immune reaction. ^[4]
• Antiseizure medicines (often levetiracetam) are used for control; benzodiazepines help abort acute seizures. ^{[16] [17]}
• In CAR T–related ICANS, care may escalate to ICU-level support, with steroids and sometimes cytokine-targeted agents considered by specialists. ^{[16] [18]}
• For high-risk patients receiving immune effector therapies, preventive antiseizure medication can be considered. ^[19]

Practical coping strategies for users and families

• Keep a simple seizure action plan with emergency steps and key contacts.
• Track symptoms daily (headache, confusion, fevers, sleep changes) and report early changes to the care team. ^[1]
• Review all medicines with your clinicians to avoid drugs that depress the central nervous system unless needed for seizure care. ^[18]
• Ensure home safety: avoid heights without supervision, take showers instead of baths, and consider protective measures in living spaces.
• Do not drive until cleared; seizure precautions are important for your safety.
• Ask your team about when to resume therapy and any monitoring (such as imaging) after recovery; decisions are individualized. ^{[2] [3]}

Special contexts

• In autoimmune epilepsy, immunotherapy (like high-dose corticosteroids or other agents) is actually used to reduce immune activity and treat seizures, which is a different situation from cancer immunotherapy side effects. ^{[20] [21]}
• Antibody therapies for other conditions (for example, anti-amyloid antibodies) can cause imaging changes that sometimes present with seizures, and management may include pausing therapy, steroids, and antiseizure medication. ^[22]

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Quick Reference: Seizures with Immunotherapy

Scenario	Key features	What clinicians may do
Checkpoint inhibitor neurologic irAEs	Headache, fever, confusion, encephalitis; seizures can occur	Urgent evaluation, corticosteroids, antiseizure meds; consider pausing drug
CAR T–related ICANS	Confusion, aphasia, somnolence; seizures; may follow cytokine release syndrome	Grading with ICE/CTCAE; ICU care for severe cases; steroids, seizure control; selective cytokine modulation
Specific drug labeling with “seizures”	Product information lists seizures as serious events	Withhold or discontinue, investigate cause, manage neurologic toxicity

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When to call your team

• Any first seizure or prolonged/repeated seizure. ^[7]
• New neurologic symptoms (persistent headache, high fever with confusion, neck stiffness, unusual behavior, focal weakness). ^{[1] [15]}
• Worsening drowsiness or difficulty being aroused. ^[7]

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Outlook

While seizures related to immunotherapy are uncommon, prompt recognition and treatment often lead to recovery, and therapy plans can be adjusted safely by your oncology team. ^[8] Early communication and a clear action plan help you stay safe and continue treatment when appropriate. ^[18]