Seizure During Infliximab Infusion in a Child With Crohn’s Disease: An Illustration of a Neurologic Adverse Event Associated With Drug Antibodies

**Background:** Anti-TNF medications like infliximab are effective for Crohn's disease but can cause infusion reactions, including rare neurologic events. Acute infusion reactions occur in 4%–18% of pediatric patients, but neurologic adverse events are uncommon and poorly understood, possibly linked to neutralizing antibodies. This report presents the first pediatric case of a seizure during infliximab infusion and explores its association with drug and antibody levels.

**Methods:** This is a single case report of a 17-year-old male with moderate-to-severe ileocolonic Crohn's disease diagnosed at age 14. He received infliximab 10 mg/kg every 8 weeks for maintenance therapy after successful induction. His course was complicated by a terminal ileum stricture and abscess requiring ileocecectomy 2 years after diagnosis. After surgery, he achieved steroid-free remission with improved symptoms and labs (fecal calprotectin improved from >1000 to 258 µg/g). After 3 years on maintenance infliximab, he developed post-infusion symptoms (abdominal pain, vomiting, headache, myalgia) lasting 24 hours, resolving within 72 hours. Premedication with acetaminophen and diphenhydramine allowed 4 uneventful infusions. During a routine infusion, within 4 minutes of initiation, he became unresponsive with generalized rhythmic jerking for 2–3 minutes, followed by confusion (postictal state). Infusion was stopped, and he was transported to the emergency department. He had no prior or family history of seizures or neurologic disorders. Emergency evaluation (blood glucose, urine toxicology, CBC, CMP, urinalysis, ECG, brain MRI) was normal. Headache and myalgia resolved with ketorolac and acetaminophen. Infliximab and anti-TNF antibody levels were measured 2 days post-event using a nonradio-labeled liquid phase mobility shift assay (Prometheus Anser). Drug levels were undetectable (<0.1 μg/mL), and anti-TNF antibody level was moderate (15.2 U/mL). The patient transitioned to adalimumab monotherapy without further convulsive events.

**Key Results:** The patient experienced a seizure during infliximab infusion with undetectable drug levels and moderate anti-TNF antibodies. No underlying neurologic condition was identified (normal MRI, normal exam, no prior seizures). Symptoms resolved completely, and no recurrence occurred on adalimumab. The report notes that patients with detectable antibodies to infliximab are 2–3 times more likely to develop infusion reactions. Background seizure prevalence in children is 5.3–8.8 per 1000, with febrile/one-time seizures at ~3.5 per 1000.

**Clinical Implications:** This case suggests that infliximab-associated seizures may be linked to immunogenicity (antibody formation) rather than direct drug toxicity. Monitoring drug and antibody levels could identify patients at risk for neurologic adverse events. Switching to another anti-TNF (adalimumab) may be safe if immunogenicity is the cause. Further studies are needed to clarify mechanisms and risk factors for neurologic side effects in pediatric patients on infliximab.