Phenytoin, is a popular drug used as an antiseizure medication sold under the brand name Dilantin. It is useful for the prevention of tonic-clonic seizures and focal seizures. Dyskinesia categorized by involuntary movement of muscle. Antiepileptic drug-induced involuntary movements have been well researched. Rare reports have been made for dyskinesia, a type of dystonia caused by phenytoin however the mechanism of its occurrence is not well known.

A new case study in Journal Of Medical Case Reports reveals that the phenytoin-induced dyskinesia in the patient was successfully reversed with prompt identification and treatment. According to the case study’s findings, such people may benefit from periodic therapeutic drug monitoring. Differential diagnosis and early management is a must note for physicians.
The case study reports a 53-year-old Asian patient taking phenytoin (100 mg twice daily) experienced symptoms of perioral muscle involuntary movement, impaired speech, and generalized tremors and was admitted to the hospital. Brain magnetic resonance imaging showed significant development of encephalomalacia and porencephaly.
The case study found that
• Patient on the third day, the serum phenytoin level was 33 g/ml (10–20 g/ml). Adverse drug reaction (ADR) causality evaluations using the World Health Organization (WHO) causality assessment scale and Naranjo’s Algorithm revealed a “probable” time–temporal link of ADR.
• On the first day, the ADR was managed by withdrawing phenytoin from the regimen. He was given supportive treatment in the form of levetiracetam 500 mg and clonazepam 0.5 mg twice daily and thrice daily, respectively.
• For three days, the patient was kept hydrated with intravenous fluids. The patient was routinely monitored. By the third day after discontinuing phenytoin, involuntary movements had stopped.
The serum level of phenytoin may or may not be non-toxic. It is critical to consider phenytoin as a differential diagnosis in any patient who exhibits involuntary movements while on phenytoin medication. This is a case with a great prognosis following drug discontinuation/withdrawal ended the authors.
Reference: Shah, K.C., Patel, N.S., Vasani, P. et al. Phenytoin-induced dyskinesia: a case report. J Med Case Reports 17, 313 (2023). https://doi.org/10.1186/s13256-023-04033-6