Phenytoin cerebellar atrophy occurs after prolonged exposure to phenytoin, usually for the management of epilepsy.
The most important factor in the development of cerebellar atrophy is the duration of phenytoin exposure 2. Approximately 30% of individuals with long-term phenytoin exposure will develop cerebellar atrophy 2.
Acute phenytoin toxicity can result in transient cerebellar dysfunction, but it is chronic exposure to therapeutic levels of phenytoin which results in permanent pancerebellar dysfunction, including ataxia, nystagmus, dysarthria, and hypotonia 2.
This differential is essentially that of other causes of diffuse cerebellar atrophy.