22.2 Seizures and PRES

CPHON TCO V.F.2–3 tests seizures and posterior reversible encephalopathy syndrome (PRES) as neurologic emergencies. This is not the chronic vincristine-neuropathy or school-504 lecture. It is also not a demand that you recite one society’s exact milligram-per-kilogram benzodiazepine table as if ONCC printed it. The product is a nurse who protects the airway, gives a benzodiazepine per Pediatric Advanced Life Support (PALS) or hospital protocol, checks glucose and electrolytes, and names the oncology trigger—including PRES—before anyone files the event as “just a febrile seizure.”

A 5-year-old who seizes during high-dose methotrexate, a 12-year-old day +18 after hematopoietic stem cell transplantation (HSCT) on tacrolimus who goes blind then convulses, and a 9-year-old after CD19 chimeric antigen receptor T-cell (CAR-T) therapy who cannot name a pencil and then seizes are three different maps that share the same first minute.

Why children on this unit seize

High-yield pediatric oncology causes:

• Electrolytes: falling sodium (SIADH, water load, cerebral salt wasting) and low calcium (tumor lysis, massive transfusion citrate, hungry-bone pictures). The metabolic-emergency chapter owns the chemistry; this chapter owns the convulsion.
• CNS disease: new or residual brain tumor, hemorrhage, infection, leukoencephalopathy, drop in perfusion.
• Methotrexate, intrathecal or high-dose intravenous, can produce acute neurotoxicity that includes seizure or a stroke-like picture. Hold further methotrexate and notify; this is not “attention-seeking.”
• Ifosfamide encephalopathy includes confusion, hallucinations, cerebellar signs, and seizures during or hours after the infusion. Stop the remaining drug; methylene blue as ordered lives with the neurologic-effects chapter. The emergency here is still airway and benzodiazepines if the child is convulsing.
• Busulfan, especially high-dose conditioning for HSCT, is epileptogenic. Protocol seizure prophylaxis (often levetiracetam; older pathways used phenytoin) is part of the conditioning checklist. A missed prophylaxis dose is a preventable seizure, not a surprise. Teach families that the “anti-seizure medicine with the chemo” is not optional.
• ICANS after CAR-T or T-cell–engaging antibodies: delirium, aphasia, seizure, cerebral edema. ICE-style checks and corticosteroids belong with cellular therapy; if the child is seizing, ABCs and benzodiazepines still go first.

Do not invent a single ONCC-mandatory glucose number. Do check glucose, because hypoglycemia is a fixable cause. Do not force objects into the mouth. Time the event. Protect from injury. Stay until the motor activity stops or the airway team takes over.

First actions: ABCs, benzodiazepines, labs

Airway, breathing, circulation first. Position to protect the airway, suction if needed, give oxygen, and do not leave a post-ictal child supine and unwatched with a full stomach. Benzodiazepines are first-line for ongoing seizure per PALS and the hospital status-epilepticus pathway (commonly intravenous lorazepam when a line is working; midazolam intramuscular, intranasal, or buccal when it is not). Use the protocol in front of you; do not delay the first dose to debate brand names. Repeat per protocol if the seizure continues. Escalate to the next-line antiseizure medicine and intensive care rather than stacking uncounted benzodiazepine syringes on the floor.

Draw glucose, sodium, and calcium (and a blood gas, complete blood count, and drug levels the team orders) as soon as you can without delaying the benzodiazepine. Correct hypoglycemia. Hyponatremic seizure is an intensive-care hypertonic-saline problem from the metabolic chapter, not more free water. Hypocalcemic tetany and seizure need calcium as ordered, with the tumor-lysis caution if phosphate is extreme.

Walk the 5-year-old during high-dose methotrexate: four minutes of generalized shaking, oxygen saturation falling, no line in the playroom. Intramuscular or intranasal midazolam per protocol, airway, glucose, sodium, calcium, notify, seizure precautions, hold the next methotrexate until the team images and decides. Do not walk the child back to the playroom because “it stopped.” Do not wait for a routine electroencephalogram tomorrow while the child is still blue.

PRES: hypertension, immunosuppression, reversible if caught

PRES is a clinicopathologic syndrome: endothelial injury and vasogenic edema, classically in posterior parietal-occipital white matter. The pediatric oncology cluster is hypertension plus immunosuppression. High-yield drugs: calcineurin inhibitors (tacrolimus, cyclosporine) after HSCT or solid-organ pathways, and corticosteroids. Other reported associations include selected chemotherapy and sudden blood-pressure spikes. Do not treat one brand as the only 2026 cause.

What you see: severe headache, visual change (blurred vision, cortical visual loss, photopsias), altered mental status, and seizures—often in a child whose blood pressure is well above that child’s baseline. A 12-year-old on tacrolimus whose usual systolic pressure is 100 mm Hg and who now reads 168/110 mm Hg with “I cannot see the television” is PRES until imaging says otherwise. Magnetic resonance imaging (MRI) classically shows posterior T2 / fluid-attenuated inversion recovery hyperintensity. Treat the child in front of you; do not withhold blood-pressure control and antiseizure care until the scanner is free.

Treatment: protect airway if seizing; benzodiazepines as above; treat hypertension with the agents the team orders—bring the pressure down in a controlled way, not a crash to shock; hold or adjust the offending drug with the transplant or oncology team. Do not unilaterally discard a graft-protecting calcineurin inhibitor in the hallway, and do not double the tacrolimus because “visual change means rejection.” Caught early, PRES is often reversible. Missed, it becomes infarction, refractory seizures, or herniation. Serial neurologic checks after the first seizure are the intervention, not a single normal pupil chart.

Distinguish look-alikes. ICANS is an immune-effector window after CAR-T or bispecifics; steroids and ICE-style exams dominate, and tocilizumab is not the automatic first drug for isolated aphasia. Methotrexate leukoencephalopathy is timed to IT or high-dose methotrexate. Stroke and CNS relapse still need imaging. Meningitis remains on the differential after HSCT, but a hypertensive, cortically blind child on tacrolimus is PRES first, not an automatic LP through a tight brain. If mass effect is in play, the last section’s LP ban still holds.

The CPHON product for TCO V.F.2–3 is a benzodiazepine that did not wait for an electroencephalogram, a glucose and sodium that left with the first blood draw, a busulfan prophylaxis dose that was actually given, and a hypertensive, visually changing HSCT patient who was named PRES before anyone doubled the tacrolimus.