Phenytoin-Induced Orofacial Dyskinesia Mimicking Anti-NMDA Receptor Encephalitis: A Diagnostic Pitfall in Postoperative Epilepsy Patients

Abstract Postoperative epilepsy patients may present with new neurological symptoms that raise concern for autoimmune or infectious etiologies. In this case, a 25-year-old man with intellectual disability and left hippocampal sclerosis underwent left temporal lobectomy and hippocampectomy. After a seizure-free interval of 45 days, he developed multiple generalized tonic–clonic seizures in the setting of a postoperative subdural hematoma. Following hematoma evacuation, he received intravenous antiseizure therapy that was complicated by a medication dosing error. Shortly thereafter, he exhibited prominent involuntary orofacial movements, confusion, and persistent electrographic abnormalities. Neuroimaging showed new, mild bilateral posterior cortical enhancement, and electroencephalography (EEG) revealed lateralized periodic discharges. The constellation of movement disorder, seizures, and EEG changes raised concern for an autoimmune encephalitis, which can occur after epilepsy surgery and requires timely immunotherapy. However, cerebrospinal fluid analysis and a comprehensive autoimmune antibody panel were unremarkable. Over the subsequent 2 weeks, symptoms resolved in parallel with normalization of antiseizure drug levels, without the use of immunotherapy. This case underscores the importance of considering medication toxicity in the differential diagnosis of acute postoperative neurological syndromes. Recognition of drug-induced phenomena can prevent both misdiagnosis of autoimmune encephalitis and unnecessary treatment delays in patients who truly require immunotherapy.