Pancerebellar syndrome due to phenytoin poisoning

Abstract

A case of pancerebellar syndrome associated with phenytoin toxicity is reported. A patient with epilepsy treated with phenytoin for years presented symptoms such as gait instability, vertigo, and lack of coordination. Tests revealed cerebellar atrophy with elevated phenytoin levels in the blood, suggesting toxicity due to accumulation.

Phenytoin is a commonly used medication for the treatment of partial and tonic-clonic seizures in epilepsy. It works by inhibiting sodium channels in neurons, thereby decreasing their excitability. Due to its narrow therapeutic window, its accumulation can exacerbate or accelerate side effects.

Cerebellar syndrome can be approached based on the chronology of symptoms like ataxia, dysmetria, intentional tremor, nystagmus, and gait instability, seeking structural, autoimmune, infectious, and toxic causes. Neuroimaging tools such as computed tomography and magnetic resonance imaging are very useful for early diagnosis and to quantify the evolution over time.

In the reported case, pancerebellar atrophy and toxic serum levels of phenytoin were detected, with no other pathological findings in imaging studies or laboratory tests to explain the clinical presentation.

Chronic use of phenytoin, both in therapeutic and toxic doses, has been associated with the development of ataxia and cerebellar atrophy, which is usually irreversible.

Based on the literature review conducted, it is proposed that in this case, cerebellar atrophy may be related to chronic phenytoin use (regardless of the dose used) and that the subacute exacerbation of the cerebellar syndrome can be attributed to the demonstrated toxic serum levels of phenytoin.