Objective: To report a rare case of phenytoin-induced generalized chorea resulting from inadvertent medication duplication across multiple healthcare facilities, highlighting a preventable cause of acute hyperkinetic movement disorder

Background: Phenytoin-associated movement disorders remain uncommon manifestations of antiseizure drug toxicity. While cerebellar dysfunction is well-recognized, hyperkinetic movements such as chorea and ballism are rarely documented, with fewer than 50 cases reported in the literature. The pathogenesis likely involves disruption of basal ganglia-thalamocortical circuits through GABAergic enhancement and dopaminergic interference at the striatal level.

Method: Case report of an 18-year-old male with well-controlled epilepsy on phenytoin 300 mg/day who developed acute-onset generalized choreiform movements. Comprehensive evaluation included neurological examination, serum phenytoin level, metabolic panel, thyroid function tests, ceruloplasmin, autoimmune markers (antinuclear antibody, antistreptolysin O titre), echocardiography, and brain magnetic resonance imaging (MRI).

Results: Neurological examination revealed bilateral horizontal nystagmus, continuous irregular choreiform movements involving face, limbs, and trunk, dysmetria, gait ataxia, and diminished reflexes. Serum phenytoin level was 25 μg/mL (therapeutic range 10-20 μg/mL). All other investigations were unremarkable. Medication reconciliation revealed concurrent prescriptions from two separate hospitals, resulting in inadvertent doubling of daily dose to 600 mg for approximately two weeks. Phenytoin was discontinued with transition to levetiracetam 500 mg twice daily. Choreiform movements resolved completely within 72 hours, with nystagmus and ataxia resolving by day five. Repeat phenytoin level at 48 hours was 15 μg/mL. The patient remained seizure-free at six-month follow-up without recurrence.

Conclusion: This case emphasizes the critical importance of systematic medication reconciliation in epilepsy management to prevent iatrogenic toxicity from duplicate prescribing across fragmented healthcare systems. Clinicians should maintain high suspicion for drug-induced hyperkinetic movements in patients on phenytoin, even with modestly supratherapeutic levels, as prompt recognition and discontinuation leads to complete reversibility.

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2. Kesavan R, Narayan SK, Adithan C: Influence of CYP2C9 and CYP2C19 genetic polymorphisms on phenytoin-induced neurological toxicity in Indian epileptic patients. Eur J Clin Pharmacol. 2010, 66:689–96. 10.1007/S00228-010-0817-2/METRICS
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MDS Abstracts - https://www.mdsabstracts.org/abstract/phenytoin-intoxication-masquerading-as-generalized-chorea-a-case-of-iatrogenic-double-prescribing/