Background: Dyskinetic neurological diseases are common presentations of adverse
reaction to many therapeutic agents. Phenytoin, a widely used age-old antiepileptic drug has been
reported to cause dyskinesias, a rare Adverse Drug Reaction (ADR) in adults with toxic therapeutic
serum level. When the drug is used in combination with other drugs which augments free drug level of
phenytoin or in patients of organic brain lesion, this side effect is very occasionally reported with even
normal therapeutic drug level.
Clinical Case: We report a case of young male presented with chorea after two months of starting
phenytoin for primary generalised epilepsy with normal therapeutic serum drug level. After excluding
other differentials, drug-induced chorea was the final diagnosis. Despite phenytoin level was in
therapeutic range, we have a trial of stopping Phenytoin with complete disappearance of chorea in 3
days. On reintroduction of phenytoin in the same dose, there was the reappearance of chorea in onemonth
re-emphasising the diagnosis as “phenytoin-induced chorea”.
Conclusion: If any patient on phenytoin develops any new neurological feature including dyskinesias,
it should be considered as an ADR despite drug serum level within the normal therapeutic range.